Dr. Jeff Masters' WunderBlog

Rare October snowstorm hammers Northeast U.S.

By: Christopher C. Burt , 10:15 PM GMT on October 30, 2011

The most extraordinary October snowstorm in over two centuries in the Northeast U.S. has finally come to an end this Sunday afternoon. Not since the infamous snow hurricane of 1804 have such prodigious amounts of snow been recorded in New England and, to a lesser extent, in the mid-Atlantic states. In fact, the snowfall, in most cases, has exceeded that of even the great October snow of 1804. Trees that had not yet lost their leaves suffered tremendous damage from the wet, heavy snow, and snapped branches and falling trees brought down numerous power lines, leaving at least 2.5 million people without electricity.


Figure 1. Heavy snow in Coopersburg, PA on October 29 brought down trees and blocked roads. Image credit: wunderphotographer boyrr.

The records are broken are simply unbelievable. New York City's Central Park location, with a period of record dating back to 1869, received an official 2.9" of snowfall, breaking the previous record of 0.8" set in 1925. The highest total in New York City itself was 6.0" at Fieldston in the Bronx. But that is a simply an afterthought compared to the 19.0" reported just 45 miles northwest of Manhattan at West Milford. New Jersey. Newark, New Jersey reported 5.2", by far their greatest October snowfall on record. And even that total pales in comparison to the astonishing figures measured in New Hampshire and Massachusetts where more than 30" has been reported. Perhaps most amazing of all is the 22.5" that fell at Concord, New Hampshire between 3pm Saturday and 7am Sunday. This the second greatest 24-hour total ever record on any date or month in Concord history. Virtually every site north of Maryland to Maine, with the exception of coastal areas, recorded their greatest October snowfall on record. True blizzard conditions were averted since the strongest winds were confined to coastal areas where the precipitation fell almost exclusively as rain. A wind gust of 69 mph was recorded at Nantucket, Massachusetts (where sustained winds of 53 mph also occurred) and Barnstable at 4am Sunday. The top wind gust on Long Island, New York was 58 mph at Sands Point.


Figure 2. Snow depth as of 2 am EDT Sunday October 29, 2011. Image credit: NOAA.

The highest snow totals by state, from the latest NOAA storm summary and NWS public information statements:

Massachusetts: 32" at Peru
New Hampshire: 31.4" at Jaffrey
Maine: 20.0" at Acton
New Jersey: 19.0" at West Milford
Connecticut: 18.6" at Bakersville
New York: 17.9" at Millbrook
Pennsylvania: 16.0" at Huffs Church, Hazleton, and Springtown
Vermont: 16.0" at West Halifax
West Virginia: 14.0" at Mount Storm
Maryland: 11.5" at Sabillasville
Rhode Island: 6.6" at West Glocester

New England's Snow Hurricane of October 9, 1804
In a post I wrote last November on record early snowstorms, I penned this account of the Great October Snow Hurricane of 1804:

Perhaps the most extraordinary early-season snowstorm in New England history occurred on Oct. 9, 1804 when a hurricane roared ashore on Long Island, New York and then encountered an arctic air mass over southeastern Canada. The winds of the hurricane caused extensive structural damage from New York to Massachusetts (where the steeple of North Church in Boston was blown down). The rain turned to snow as far south as the Connecticut River Valley in Connecticut, where low elevation towns from here to the Canadian border received 4-6" of snow, and the higher terrain of Vermont up to three feet of accumulation. In Vermont, drifts buried fences and blocked roads. The Catskills of New York reported 12-18"; the Berkshires of Massachusetts received 24-30". Even coastal New Haven reported some snow (and 3.66" of rain). Reference: "Early American Winters: 1604-1820", by David M. Ludlum, American Meteorological Society, 1966, and "Early American Hurricanes, 1492-1870", by the same author.

Given what we have just seen it is probably safe to concluded that this weekend's event was of even greater magnitude than the 1804 storm although three weeks later in the season.

Wunderground weather historian, Christopher C. Burt

New York City's 3rd wettest year on record
The 2.01 inches of precipitation that fell in New York City in Saturday's storm brought the city's year-to-date total to 65.75", which is 24.10" above normal, and makes it the third wettest year in New York City history. With two months still left in the year, New York City has a chance to beat its all-time wettest year in history, the 80.56" that fell in 1980. Records date back to 1869.

Early season snowfalls and climate change
Naturally, the occurrence of a record early-season snow storm will lead to cries of "what happened to global warming?" Global warming theory does predict that we should see a decrease in early-season and late season snow as the climate warms, since it will not be cold enough to snow. However, the climate models also predict that we may see an increase in the intensity of the strongest winter storms, like the Nor'easter that dumped the record October snows over the Northeast on Saturday, and it is important to realize that snow is not the same thing as cold. Temperatures in the Northeast U.S. were quite cold on Saturday, but no observing station there broke a record for coldest temperature for the day on October 29, according to the National Climatic Data Center. Our climate is still cold enough in October to give us the occasional early-season record snowstorm.

Quiet in the Atlantic
There are no threat areas to discuss in the Atlantic, and none of the reliable computer models are showing development of a new tropical depression in the Atlantic over the next seven days.

I'll have a new post on Tuesday morning.

Jeff Masters

Winter Weather

Updated: 6:06 PM GMT on October 31, 2011

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Rina pulls its punch; Thai floods worsen; Texas gets snow

By: JeffMasters, 2:34 PM GMT on October 28, 2011

Tropical Storm Rina is being ripped apart by strong upper-level southerly winds creating 30 knots of wind shear over the storm. Visible satellite loops show that the low-level circulation of Rina is just a naked swirl over Cancun, on the northeastern tip of the Yucatan Peninsula. The shear has torn away Rina's heavy thunderstorms so that they lie about 200 miles to the northeast of the center. Cancun radar shows almost no rain affecting the northeastern Yucatan Peninsula and surrounding the waters, even though the center of the storm is directly over Cancun. Last night, Rina brought wind gusts of up to 41 mph to Cancun and 43 mph at Cozumel, where 8.20" of rain fell yesterday. Damage from Rina to Cozumel and Cancun should be very minor, and I expect the hotels there will be open for business today.

Rina will continue to be sheared apart today, with the low level center expected to drift slowly southwards along the Yucatan coast. Long range radar out of Key West shows that moisture streaming to the northeast from Rina is bringing rain to the Southwest coast of Florida. Rainfall amounts of 1 - 3 inches are likely over the Florida Keys and South Florida through Sunday due to moisture from Rina. Wind shear should be able to destroy the circulation of Rina by Saturday.


Figure 1. What tropical storm? It's hard to tell a tropical storm with 45 mph winds was centered over this beach in Cancun, Mexico this morning. Rina's heavy rains and strong wind were several hundred miles to the northeast of Cancun this morning, thanks to strong upper-level winds that sheared the storm apart.


Figure 2. Morning satellite image of Tropical Storm Rina showing the center of circulation over the northeast tip of the Yucatan Peninsula, and the heavy thunderstorms several hundred miles to the northeast of the center.

Elsewhere in the Atlantic
A broad region of low pressure in the Western Caribbean between Jamaica and Honduras is drifting slowly northwest at less than 5 mph. Heavy thunderstorm activity is disorganized and relatively modest, and NHC is giving the region a 10% chance of developing into a tropical depression by Sunday. Heavy rains from the disturbance will affect Honduras, the Cayman Islands, and Nicaragua Friday through Sunday. None of the reliable computer models are showing development of a new tropical depression in the Atlantic over the next seven days, though we will continue to see disturbed weather over the Western Caribbean that could generate something.

Thailand's Great Flood likely to peak this weekend
The most damaging natural disaster in Thailand history is growing more serious, as the flood waters besieging the capital of Bangkok continue to overwhelm defenses and inundate the city. Heavy rains during September and October have led to extreme flooding that has killed 373 people and caused that nation's most expensive natural disaster in history, with a cost now estimated at $6 billion. Thailand's previous most expensive disaster was the $1.3 billion price tag of the November 27, 1993 flood, according to the Centre for Research on the Epidemiology of Disasters (CRED). Floodwaters have swamped fields and cities in a third of Thailand's provinces, affected 9 million people, and damaged approximately 10% of the nation's rice crop. Thailand is the world's largest exporter of rice, so the disaster may put further upward pressure on world food prices, which are already at the highest levels since the late 1970s. The highest tide of the month occurs this weekend at 8:07 am ICT in the capital of Bangkok, and the additional pressure that incoming salt water puts on the flood walls protecting the city is a major concern. Fortunately, the monsoon has been quiet this week over Southeast Asia, and the latest GFS model precipitation forecast show little additional rain over the country in the coming week. Heavy monsoon rains are common in Thailand and Southeast Asia during La Niña events, and we currently have a weak La Niña event occurring. Ocean temperatures in the waters surrounding Thailand during September and October have been approximately 0.3°C above average, which has increased rainfall amounts by putting more water vapor into the air. The remains of Tropical Storm Haitang and Typhoon Nesat also brought heavy rains in late September which contributed to the flooding.


Figure 3. Top ten most expensive natural disasters in Thailand since 1900, as tabulated by the Centre for Research on the Epidemiology of Disasters (CRED). This month's disaster (number one on the table above) is not yet in the CRED data base.

Texas gets its first snow of the season
The first snow of the season blanketed parts of the western and central Oklahoma and Texas Panhandles yesterday. Officially, Amarillo, TX picked up 3.1" of snow, which was a record for the date (old record: 2.4" on Oct. 27, 1911.) Areas 6 miles southwest of Amarillo got up to five inches of snow. Amarillo's heaviest October snow on record was 9.0" on Oct.21 - 22, 1906. The earliest measurable snowfall at Amarillo is 0.3" on Sept. 29, 1984. Yesterday's snow was quite a contrast from Tuesday's weather, when the high hit 86°F in Amarillo! Normally Texas would grumble about getting snow so early in the year, but yesterday's 1.23" of precipitation in Amarillo was over 25% of their precipitation for the entire year. Amarillo has now had 4.84" of precipitation this year, which is almost 14" below normal. Wunderground's weather historian Christopher C. Burt has the latest on the Texas drought in his latest post. He noted that Pecos, TX had received a paltry .48" so far this year, and that the driest calendar year in Texas records was 1.64" at Presidio in 1956. Well, Pecos got another 0.02" yesterday to bring their yearly total to 0.50", so that city is still on track to record the lowest rainfall of any city in Texas history.

My next post may not be until Sunday or Monday, depending upon the weather.

Jeff Masters

Flood Hurricane

Updated: 2:36 PM GMT on October 28, 2011

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Tropical Storm Rina continues to deteriorate; close to landfall in Mexico

By: angelafritz , 9:19 PM GMT on October 27, 2011

Tropical Storm Rina has taken a beating in the past 48 hours. Between a mass of dry air to its west and strong southerly wind shear, Rina has not been able to overcome its environment. At 5pm EDT, Rina had maximum sustained winds of 60 mph and was moving north at 7 mph. At 3:30pm EDT, Rina was located about 50 miles south of Cozumel. The most recent Hurricane Hunter mission found surface wind speeds of around 55 mph (moderate tropical storm-strength) on the north side of the storm and central pressure of 993 mb and rising. Rina's thunderstorm activity has decreased markedly since yesterday. The storm is battling a whopping 30 knots of wind shear, and its surface center is becoming exposed again this evening, which is apparent on satellite.

Wind speed on Cozumel is a breezy 10-15 mph with gusts to 25 mph. The island has received 0.28 inches of rain so far today, and it doesn't look like it's going to get much more than that. At Cancun, winds are blowing at 8 mph with gusts up to 15 mph and wave height on the beach is pretty low.


Figure 1. Infrared satellite imagery shows Rina's thunderstorm activity has all but disappeared, and the surface center is exposed, likely due to the high wind shear from the south. Source: NOAA.


Forecast for Tropical Storm Rina
The official forecast from the National Hurricane Center is for Rina to make landfall near Cozumel later this evening as a tropical storm. Over the next 48 hours, Rina is expected to weaken to a tropical depression as a cold front nudges it back into the Caribbean (Figure 2). The GFS is forecasting Rina to re-intensify to around 55 mph early next week. The ECMWF was predicting a similar event in this morning's forecast but has since backed off, and the HWRF agrees. The most likely scenario is that Rina's remnants will linger in the western Caribbean through the beginning of next week before finally dissolving into the surrounding environment.



Figure 2. Surface forecast for Saturday morning from NOAA's Hydrometeorological Prediction Center. A cold front dipping south into the Caribbean will be responsible for kicking Rina back into the Caribbean.

Angela

Hurricane

Updated: 9:24 PM GMT on October 27, 2011

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Rina continues to weaken; nearing landfall in Mexico

By: JeffMasters, 2:14 PM GMT on October 27, 2011

Hurricane Rina continues to decay, thanks to strong upper-level southerly winds that have created 20 knots of wind shear and torn into the south side of the storm. A NOAA hurricane hunter aircraft is in Rina, and found top winds of 71 mph at the surface with their SFMR surface wind measurement instrument, and 62 mph at their flight level of 10,000 feet, during their first penetration through the center at 9:27 am EDT. These data suggests that Rina is on the verge of becoming a tropical storm. Visible satellite loops show that Rina is just a shell of its former self, with just a small mis-shapen lump of heavy thunderstorms near the center, no eye, and little in the way of spiral bands. Cancun radar shows disorganized heavy rain squalls are affecting the northeastern Yucatan Peninsula and surrounding the waters, and it is difficult to tell from the echoes that there is a tropical storm or hurricane out there. When Rina peaked in strength yesterday with 110 mph winds, it was the 13th strongest Atlantic hurricane so late in the season. But, because it was such a small storm, Rina was very vulnerable to the persistent wind shear of 15 - 20 knots that affected it, especially once it moved away from a "hot spot" in the ocean waters southeast of the Yucatan last night. Rina should continue to decay today, and will probably make landfall as a tropical storm with 60 - 70 mph winds late this afternoon or early this evening. So far this morning, winds at Cozumel have been under 15 mph, and the island had picked up 0.35" of rainfall as of 10 am EDT. Damage from Rina to Cozumel and Cancun should be minor, and I expect the hotels there will be open for business this weekend.

After Rina makes its closest pass by Cozumel, the storm will be too weak and shallow to "feel" the steering influence of a trough of low pressure passing to its north, and Rina will be trapped in the Western Caribbean near the coast of the Yucatan. Wind shear may be strong enough to destroy the storm by Monday. Moisture streaming to the northeast from Rina is likely to bring 1 - 3 inches of rain to the Florida Keys and South Florida over the weekend.


Figure 1. Dark clouds over paradise: a wunderground webcam from Playa Del Carmen, across the channel from Cozumel Island, shows the storm clouds from Rina approaching the island at 10:06 am EDT this morning.


Figure 2. Morning radar image of Rina from the Cancun, Mexico radar at 9:30 am EDT October 27, 2011. Image credit: Sevicio Meteorologico Nacional, Mexico.


Figure 3. True-color MODIS image of Hurricane Rina taken at 3:10 pm EDT October 26, 2011. At the time, Rina was a Category 1 hurricane with 85 mph winds. Image credit: NASA.

Elsewhere in the Atlantic
A broad region of low pressure in the Western Caribbean south of Jamaica (Invest 97L), is moving west at 10 - 15 mph. Heavy thunderstorm activity associated with 97L is disorganized and relatively modest, and NHC is no longer interested enough in 97L to generate computer model forecasts of its track. Heavy rains from 97L will spread over Honduras and Nicaragua tonight and Friday. None of the reliable computer models are developing 97L, and I don't expect development.

The NOGAPS and GFS models are predicting that a strong tropical disturbance capable of developing into a tropical depression could form off the Caribbean coast of Nicaragua 7 - 8 days from now.

There will be a new post on Rina late this afternoon.

Jeff Masters

Hurricane

Updated: 4:05 PM GMT on October 27, 2011

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Hurricane Rina weakens as it slides toward the Yucatan

By: angelafritz , 9:12 PM GMT on October 26, 2011

Hurricane Rina has unraveled a bit since yesterday afternoon, but still packs category 1 winds of 85 mph. Rina is moving steadily to the northwest at 6 mph, and the center of the hurricane is expected to reach the coast of the Yucatan Peninsula Thursday afternoon. The most recent Hurricane Hunter mission, which ended at 4:30pm EDT, found maximum surface winds around 85 mph, and a minimum central pressure of 976mb. Rina is battling some moderate wind shear (at least 10-15 knots) this afternoon, which is helping to break down the upper-level outflow of the hurricane, which is now only present on the northeast side of the cyclone. The most recent integrated kinetic energy analysis of the hurricane (Figure 1) illustrates Rina's disorganization, with the strongest winds (in yellow) located on the northeast side. The southern end of the storm looks rather bare, likely due to moderately strong southerly wind shear, which is acting to tear that side of the hurricane apart. The destructive potential rating, which is estimated by NOAA's Hurricane Research Division, has is now 1.5 for wind and 2.0 for storm surge and waves on a 0 to 6 scale.

Despite its ragged appearance and obvious weakening, Hurricane Rina is still expected to bring heavy rain and strong wind gusts to the Yucatan Peninsula. Wind speed on Cozumel had been steadily increasing since this morning, though have leveled off in the past few hours. Wind speed will increase again soon as Rina moves closer to the island. This station has also reported 3.25 inches of rain so far, but like Jeff said in this morning's blog, surrounding personal weather stations have only reported up to an inch of rain. Cancun's radar shows Rina's outer bands moving over the peninsula, and strong rain was reported in the city earlier this afternoon. A Yucatan Basin buoy is reporting wind speeds close to 30 mph, and waves around 8 feet so far. Having seen some photos of the Cancun beaches, wave height has increased there, as well, although aren't near 8 feet quite yet.


Figure 1. Hurricane Rina's wind analysis from NOAA's Hurricane Research Division.


Figure 2. Visible satellite image of Hurricane Rina taken at 4:31pm EDT.

Forecast for Hurricane Rina
The forecast for Rina remains mostly in line with earlier forecasts, although the intensity has been decreased significantly and the track through Friday has shifted slightly to the east. Rina will continue to move north-northwest toward Cozumel over the next 24 hours, likely making landfall Thursday afternoon and evening. Beyond this, the models have changed their tune since yesterday. The ECMWF, GFS and HWRF are all forecasting Rina to weaken significantly after coming in contact with the Yucatan Peninsula, but instead of a forecast track toward southern Florida, they are now calling for Rina to linger in the Caribbean as a broad area of low pressure and disturbed weather until the middle of next week, when it finally is swept out by a trough. The official forecasts from the National Hurricane Center have conveyed this possibility well in the 4 and 5 day track forecasts so far. This afternoon, they're calling for Rina to weaken to a tropical storm after landfall, at which point it will begin its clockwise turn back into the Caribbean while weakening further to a depression. The forecast surge has decreased to 2 to 4 feet, likely due to both the weakening of the hurricane and its relatively small wind radius, and heavy rain and flooding are still a concern for the Yucatan and Cozumel.

Jeff will be back with a morning post tomorrow.

Angela

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Rina still a Cat 2, and may have peaked in intensity

By: JeffMasters, 1:48 PM GMT on October 26, 2011

There is little change to Category 2 Hurricane Rina, which continues slowly west-northwest at 4 mph towards Mexico's Yucatan Peninsula. The most recent hurricane hunter mission was at 3:58 am EDT this morning, and the next aircraft is not due into the storm until this afternoon, so we'll have to rely on satellite estimates of the storm's strength until then. Recent satellite intensity estimates suggest Rina has peaked in intensity, and may have weakened slightly since the last hurricane hunter mission. The eye is no longer visible on visible satellite loops, and the storm has a distinctly lopsided appearance, which are both signs that Rina may be weakening. Recent microwave images (Figure 1) suggest that the southern portion of Rina's eyewall may have a gap in it. Wind shear is a moderate 10 - 20 knots due to upper-level winds out of the south. Water temperatures are very warm, 29 - 30°C, but Rina will be leaving a region of high oceanic heat content late tonight, and will not have as much high-energy fuel to sustain itself. Rina has brought sporadic heavy rain squalls to the Yucatan; Cozumel Island airport reported 9.10" of rain yesterday and another 3.25" as of 9 am EDT today. I'm not sure this is correct, since two personal weather stations on the island reported only 1 - 2" of rain over the past two days. The outer rain bands of Rina are visible on Cancun radar and the La Bajada, Cuba radar.

If Rina does make it to Category 3 strength, it would join a very short list of major hurricanes that have occurred this late in the year. Since record keeping began in 1851, there have been only twelve major hurricanes in Atlantic on October 26 or later. Rina is a medium-small hurricane, with hurricane-force winds that extend out 25 miles from the center. The latest estimates of Rina's Integrated Kinetic Energy (IKE) made yesterday afternoon by NOAA's Hurricane Research Division put the damage potential of Rina's storm surge at 2.5 on a scale of one to six. This is a relatively low number for a Category 2 hurricane, and means that storm surge damage will be confined to a relatively small area in the right front quadrant of Rina's eyewall. For comparison, the storm surge damage potential for Hurricane Irene when it was a strong tropical storm approaching Long Island, New York on August 28, 2011 was 4.1 on a scale of 1 to 6, since Irene was a huge storm that put vast areas of the ocean into motion.


Figure 1. Microwave satellite image of Hurricane Rina taken at 7:15 am EDT October 26, 2011. Rina appears to only have the northern half of its eyewall intact. Image credit: Navy Research Lab, Monterey.

Forecast for Rina
The hurricane hunters found that Rina had a large elliptical eye with a diameter of 23 - 34 miles with a gap in the south eyewall during their 3:58 am EDT eye penetration this morning. Rapid intensification usually requires a circular eye with no gap in it, and thus I expect only gradual intensification of Rina can occur today. Wind shear is not expected to increase to the high range until Thursday afternoon, so Rina still has a day and a half to potentially intensify. Given the storm's inability to close off its eyewall so far, I expect that a Category 3 storm is the strongest that we will see. It is more likely that Rina has peaked in strength, and will begin to weaken. On Thursday, Rina will encounter high wind shear associated with upper-level westerly winds associated with the jet stream and a trough of low pressure moving through the Gulf of Mexico. These conditions should weaken the hurricane, and turn Rina more to the northwest by Thursday and northeast on Friday. Cozumel Island off the coast of Mexico's Yucatan Peninsula appears at the highest risk of receiving a direct hit from Rina; the 5 am EDT Wind Probability Forecast from NHC gave the island a 27% chance of receiving hurricane force winds, the highest chance of any land area in the forecast. If Rina hits Mexico, it would most likely be at Category 1 strength, with Category 2 strength also quite possible. NHC is giving Rina a 21% chance of being a Category 3 or stronger hurricane on Thursday afternoon, and I don't expect the storm will be a major hurricane at landfall. The chief threat from Rina is probably its rains; the hurricane is moving slowly and has the capability of dumping 8 - 16 inches of rain over the coastal Yucatan. Western Cuba is also at risk of receiving heavy rains of 5 - 10 inches.

After Rina makes its closest pass by Cozumel, it is uncertain if the storm will be strong enough to fully "feel" the steering influence of the trough, and be swept to the east-northeast into Southwest Florida and the Florida Keys. If Rina makes landfall in the Yucatan Peninsula and weakens significantly, the storm will likely be too weak to get caught up by the trough and will remain trapped in the Western Caribbean. This is the solution of the latest runs of the ECMWF and HWRF models, with the usually reliable ECMWF model continuing to predict that Rina will dissipate over the Yucatan. However, if Rina grazes the Yucatan and remains strong through Friday, it is more likely to get caught up by the trough and drawn into the Florida Keys or Southwest Florida near Marco Island, as a weakening tropical storm. This is the solution of the latest 2 am EDT run of the GFDL model. The latest 2 am EDT runs of the GFS and NOGAPS models are in-between, predicting that Rina will get very close to the Keys on Saturday, but then weaken and sink southwards towards Cuba. There is high degree of uncertainty which set of model runs will be correct, and the threat to Florida depends strongly upon how much of a blow Mexico receives from the hurricane.

97L in the Central Caribbean not expected to develop
A broad region of low pressure in the Central Caribbean south of Haiti and the Dominican Republic, (Invest 97L), is moving west at 10 - 15 mph. Heavy thunderstorm activity has decreased since yesterday, and is disorganized. The storm is surrounded by a large region of dry air, and this dry air is the main impediment to development. Wind shear is a low 5 - 10 knots, and is expected to remain low through Thursday. None of the reliable models are predicting that 97L will develop, and NHC gave 97L just a 10% chance of developing into a tropical depression by Friday, in their 8 am EDT Tropical Weather Outlook. NHC is no longer interested enough in 97L to generate computer model forecasts of its track. Heavy rains from 97L should reach Jamaica on Thursday, and the Cayman Islands by early Friday morning.

There will be a new post on Rina late this afternoon.

Jeff Masters

Hurricane

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Hurricane Rina a strong category 2

By: angelafritz , 9:16 PM GMT on October 25, 2011

Hurricane Rina is now a strong category 2, and is slowly moving west-northwest toward Belize and the Yucatan Peninsula. Rina is packing winds of 110 mph and is crawling west at a 3 mph. Cancun radar shows some showers approaching the peninsula. Since this morning, satellite imagery has shown Rina becoming slightly more organized, and outflow has increased on all sides of the hurricane. Rina's eye appeared this afternoon, as well, though clouds continue to obscure it most of the time. Recent satellite images suggest thunderstorm activity is increasing around the eye (Figure 1). At 2pm EDT, wind shear was low (5-10 knots) near the cyclone, which is likely aiding it to intensify, but shear expected to increase over the next couple of days. This afternoon's Hurricane Hunter mission reported maximum surface winds of 108 mph north of the eye using the SMFR surface wind instrument, an observation that was not flagged for poor data quality. If the current satellite imagery and organization of the hurricane is indicative, Rina will probably reach major hurricane status tonight or early tomorrow. Another Hurricane Hunter mission is on the way to Rina this evening, and a NOAA-9 Gulfstream is also currently investigating the hurricane and sending back dropsonde information, which will be valuable for model forecasts.


Figure 1. Infrared satellite imagery of Rina taken around 12:45pm EDT on October 25. Image source: NOAA.

Forecast for Hurricane Rina
The forecast for Rina hasn't changed much since this morning. Some intensification is expected over the next 12 hours, though its slow speed could act to decrease sea surface temperatures around the hurricane, and thus decrease the amount of fuel available for further intensification. This afternoon's computer model runs continue to be somewhat divided on the likely track for the hurricane, although they seem to be coming into agreement that Rina will struggle to maintain its intensity after the land interaction with the Yucatan, as well as the high shear it will encounter in the coming days. The GFS continues to forecast that Rina will remain intact after a brief brush with the Yucatan before turning northeast and heading toward southern Florida. The HWRF model is also predicting a similar outcome. The ECMWF, on the other hand, is sticking to its forecast that Rina will lose organization once it reaches the Peninsula, and instead providing a heavy rain event for Florida in conjunction with the trough of low pressure that is expected to move through later this week.

The official forecast from the National Hurricane Center is for Rina to continue to move to the west-northwest over the next 12 hours before turning to the north toward the tip of the Yucatan. This initial forecast is in agreement with the GFS and HWRF tracks, though beyond Thursday, the Center is forecasting Rina to decrease in intensity and make a hard right turn toward the Florida Straits. Regardless, people in Belize and especially the Yucatan Peninsula should be prepared for major hurricane conditions, including a storm surge up to 7 feet above normal tide conditions, and rainfall up to 16 inches.

Jeff will be back tomorrow morning with an update.

Angela

Hurricane

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Hurricane Rina a Category 2, headed towards the Yucatan

By: JeffMasters, 1:52 PM GMT on October 25, 2011

Hurricane Rina is now a Category 2 storm, headed slowly west-northwest at 3 mph towards Mexico's Yucatan Peninsula. The most recent hurricane hunter mission was at 4:32 am EDT this morning, and the next aircraft is not due into the storm until this afternoon, so we'll have to rely on satellite estimates of the storm's strength until then. Recent satellite intensity estimates suggest Rina has leveled off in intensity, with no change in strength since the last hurricane hunter mission. A murky, cloud-filled eye is visible on visible satellite loops right now. Rina also has an impressive upper-level outflow channel to the north, and very intense thunderstorms with cold clouds tops that extend up to the stratosphere. Wind shear is a moderate 15 - 20 knots due to strong upper-level winds out of the south, and these winds are injecting dry air into Rina's south side, inhibiting heavy thunderstorm development there. Water temperatures are very warm, 29 - 30°C, and these warm waters extend to great depth. Rina has brought sporadic heavy rain squalls to the Cayman Islands; George Town on Grand Cayman has received 4.76" of rain over the past three days from Rina, as of 9 am EDT this morning.


Figure 1. True-color MODIS image of Tropical Storm Rina taken at 12:15 pm EDT October 24, 2011. Two hours after this image was taken Rina had intensified into a Category 1 hurricane with 75 mph winds. Image credit: NASA.

Forecast for Rina
The hurricane hunters found Rina's eyewall had a gap in it during their 4:32 am EDT eye penetration this morning, probably caused by the moderate wind shear the storm has experienced over the past day. It is unlikely that Rina will be able to "bomb" and undergo rapid intensification unless it can close off this gap in the eyewall. Wind shear is not expected to increase until Wednesday night, so Rina still has a day and a half to continue its intensification process. Given the storm's inability to close off its eyewall so far, I expect that a Category 3 storm is the strongest that we will see. On Wednesday night, Rina will encounter a dry airmass with high wind shear that lies over the extreme northwestern Caribbean. These conditions should weaken the hurricane, but Rina could still be a major hurricane if it makes landfall in the Yucatan Peninsula on Thursday.

A trough of low pressure is predicted to pass to the north of Rina late this week, which should turn Rina more to the northwest by Thursday and northeast on Friday. However, it is uncertain if Rina will be strong enough to fully "feel" the steering influence of this through and be swept to the east-northeast into Southwest Florida and the Florida Keys. If Rina makes landfall in the Yucatan Peninsula and weakens significantly, the storm will likely be too weak to get caught up by the trough and will remain trapped in the Western Caribbean. This is the solution of the latest runs of the ECMWF, UKMET, and HWRF models. However, if Rina remains strong through Friday, it is more likely to get caught up by the trough and drawn into the Florida Keys as a weakening tropical storm on Friday or Saturday. This is the solution of the latest 2 am EDT runs of the GFDL and GFS models. There is high degree of uncertainty which set of model runs will be correct.

Comparing Rina to Hurricane Wilma of 2005
Rina's intensification into a hurricane over the Western Caribbean during the last half of October brings to mind Hurricane Wilma, which also did this in 2005. Wilma went on to become a Category 5 monster, the strongest Atlantic hurricane of all-time. I don't think Rina will be another Wilma, even though the ocean temperatures and total heat content are similar to what Wilma experienced (Figure 3). Wilma had nearly ideal upper-level atmospheric conditions with an anticyclone aloft and light wind shear, under 5 knots. Rina is experiencing 15 - 20 knots of wind shear and is also a smaller storm, and is thus more vulnerable to the effects of wind shear and dry air.


Figure 2. Hurricane Wilma at 8:22 a.m. CDT Oct. 19, 2005 as photographed by the crew aboard NASA's international space station as the complex flew 222 miles above the storm. At the time, Wilma was the strongest Atlantic hurricane in history, with a central pressure of 882 mb and winds of 185 mph. The storm was located in the Caribbean Sea, 340 miles southeast of Cozumel, Mexico, and had an eye just 2.3 miles in diameter, the smallest on record.


Figure 3. The total heat content of the ocean available to fuel hurricane intensification as measured by the Tropical Cyclone Heat Potential (TCHP). Top: TCHP for October 23, 2011, one day before Hurricane Rina of 2011 formed. Bottom: TCHP for October 18, 2005, the day Hurricane Wilma formed. TCHP values in excess of 80 kJ per centimeter squared (yellow colors) are often associated with rapid intensification of hurricanes. Both hurricane had similar very high levels of TCHP to help fuel intensification. Image credit: NOAA/AOML


Figure 4. Wind shear in knots for 09 UTC October 25, 2011, during Hurricane Rina of 2011 (top) and at 21 UTC October 17, 2005, the day before Wilma became a hurricane. A large area of wind shear less than 5 knots lay over Wilma as it was forming, while Rina was under wind shear of 20 knots this morning. Image credit: University of Wisconsin CIMSS.

97L north of the ABC islands
A broad region of low pressure between the ABC islands of Aruba, Bonaire, and Curacao and the Dominican Republic (Invest 97L), is moving west-northwest at 15 - 20 mph. Heavy thunderstorm activity has decreased a little since yesterday, and the activity is not organized into spiral bands, as is apparent from Curacao radar. The storm is surrounded by a large region of dry air, and this dry air is the main impediment to development. Wind shear is a low 5 - 10 knots, and is expected to remain low through Thursday, and 97L will encounter a moister atmosphere as it progresses westward into the Central Caribbean. By the time 97L reaches the region between Jamaica and Nicaragua on Thursday, the storm could develop into a tropical depression. However, none of the reliable models are predicting that 97L will develop. NHC gave 97L a 30% chance of developing into a tropical depression by Thursday, in their 8 am EDT Tropical Weather Outlook. Heavy rains from 97L should reach Jamaica on Thursday, the Cayman Islands by early Friday morning, and south-central Cuba by Friday night.

Geomagentic storm triggers brilliant aurora displays
A Coronal Mass Ejection (CME) that blasted away a portion of the sun's atmosphere earlier this week hit the Earth's magnetic field at 2 pm EDT yesterday. The resulting show of Northern Lights was observed as far south as Arkansas last night. Here in Michigan, I got a call from a neighbor's 12-year old, who was concerned that the sky was all red. Alas, the display was gone by the time I had finished explaining in far too much technical detail what was behind the event!

I'll have a new post on Rina this afternoon.

Jeff Masters

Hurricane

Updated: 1:56 PM GMT on October 25, 2011

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Rina rapidly intensifies into a hurricane

By: JeffMasters, 7:59 PM GMT on October 24, 2011

Rina is now a hurricane, just 21 hours after becoming a tropical depression. An Air Force Reserve hurricane hunter aircraft found winds of 75 mph--Category 1 hurricane strength--at 1:40 pm EDT in the north eyewall of Rina, using their SFMR surface wind instrument. Winds at flight level of 5,000 feet peaked at 78 mph, which typically translates to surface winds of 62 mph. On their second pass through the eye at 3:30 pm EDT, the winds were about 5 mph less, but the central pressure had fallen by two millibars, to 989 mb. Visible satellite loops show that Rina now has an eye, and the storm is steadily expanding in size and developing an impressive upper-level outflow channel to the north. Wind shear is a moderate 15 - 20 knots due to strong upper-level winds out of the southeast, and these winds are injecting dry air into Rina's southeast side, inhibiting heavy thunderstorm development there. Water temperatures are very warm, 29 - 30°C, and these warm waters extend to great depth.


Figure 1. Afternoon satellite image of Rina. An intense thunderstorm with a top that reaches into the stratosphere is visible on the southwest side of the eye. These "hot towers" are commonly seen in hurricanes undergoing rapid intensification.

Rina in historical context
Rina intensified into a hurricane just 21 hours after the first advisory was issued for it as a tropical depression. This is the second fastest such intensification since record keeping began in 1851. Hurricane Humberto of 2007 holds the Atlantic record for fastest intensification from first advisory issued to hurricane strength--18 hours. (Actually, Humberto did the feat in 14 1/4 hours, but this was rounded off to 18 hours in the final data base, which stores points every six hours). There have been six storms that accomplished the feat in 24 hours. Rina's formation brings this year's tally of hurricanes to six, which is average for an Atlantic hurricane season. The number of named storms this season is now seventeen, making it the 7th busiest Atlantic hurricane season since record keeping began in 1851. Only 2005, 1933, 1995, 1887, 2010, and 1969 had more named storms. However, 2011 has had an unusually low percentage of its named storms reach hurricane strength. Only 35% of this year's named storms have made it to hurricane strength, and normally 55 - 60% of all named storms intensify to hurricane strength in the Atlantic. The rare combination of near-record ocean temperatures but unusually dry, stable air over the Atlantic is no doubt at least partially responsible for this very unusual occurrence.


Figure 2. Microwave satellite image from 11:39 am EDT October 24, 2011, showing that Rina had a partially complete eyewall, which was open on the east side. Image credit: Navy Research Lab, Monterey.

Forecast for Rina
The hurricane hunters found an elliptical eyewall that had a gap in it during their 3:30 pm eye penetration. The aircraft measured a temperature difference of 6°C between the eye and the region outside the eye, which is difficult to get unless an eyewall is on its way to completion. Rina will need to complete its eyewall if it is to intensify into a major hurricane. Given the fact wind shear is not expected to increase until Wednesday, Rina has a 2-day period to close off an eyewall and intensify, and it will probably reach Category 3 or Category 4 strength by Wednesday. On Wednesday, Rina will encounter a dry airmass with high wind shear that lies over the extreme northwestern Caribbean. These conditions should weaken the hurricane, but Rina could still be a major hurricane if it makes landfall in the Yucatan Peninsula on Wednesday or Thursday.

A trough of low pressure is predicted to pass to the north of Rina late this week, and now that the hurricane is expected to be a Category 2 or stronger storm, the chances for Rina to make it farther north and affect the Florida Keys and Southwest Florida have increased. The latest 8 am EDT runs of the GFDL and HWRF models both predict that Rina will pass through the Yucatan Channel on Thursday and make landfall on Friday in the Florida Keys or extreme Southwest Florida, south of Naples. The NOGAPS and GFS models predict a weaker storm, and keep Rina trapped in the Caribbean. I think it is more likely that Rina will pass through the Keys. If Rina does make it to the Keys, it would likely be as a tropical storm, since wind shear, dry air, and possible land interaction with Western Cuba and Mexico would potentially knock down the storm's strength. Heavy rains from Rina should begin affecting Mexico's Yucatan Peninsula, northern Belize, and extreme Western Cuba on Wednesday. Rina's intensification into a hurricane over the Western Caribbean during the last half of October bring to mind Hurricane Wilma, which also performed such a feat in 2005. Wilma went on to become a Category 5 monster, the strongest Atlantic hurricane of all-time. I don't think Rina will be another Wilma, even though the ocean temperatures and total heat content are similar to what Wilma experienced. Wilma had nearly ideal upper-level atmospheric conditions with an anticyclone aloft and light wind shear, under 5 knots. Rina is experiencing 15 - 20 knots of wind shear and is also a smaller storm, and is thus more vulnerable to the effects of wind shear and dry air.

97L approaching ABC islands
A broad region of low pressure approaching the ABC islands of Aruba, Bonaire, and Curacao (Invest 97L), is moving west-northwest at 10 mph. Heavy thunderstorm activity has increased today, but the activity is not organized into spiral bands, as is apparent from Curacao radar. 97L is surrounded by a large region of dry air, and this dry air will retard development. 97L is under low wind shear less than 10 knots, and this shear is expected to remain low through Thursday. By the time 97L reaches the region between Jamaica and Nicaragua in the Central Caribbean on Thursday or Friday, the storm should find a moister environment, and could develop into a tropical depression. However, none of the reliable models are predicting that 97L will develop. NHC is giving 97L just a 10% chance of developing into a tropical depression by Wednesday. I put the odds higher, at 20%.

Jeff Masters

Hurricane

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Tropical Storm Rina forms

By: JeffMasters, 1:49 PM GMT on October 24, 2011

Tropical Storm Rina formed in the Western Caribbean Sea just off the coast of Honduras last night, and is headed north-northwest towards Mexico's Yucatan Peninsula. Rina's formation brings this year's tally of named storms to seventeen, making it the 7th busiest Atlantic hurricane season since record keeping began in 1851. Only 2005, 1933, 1995, 1887, 2010, and 1969 had more named storms. However, 2011 has had an unusually low percentage of its named storms reach hurricane strength. Only 29% of this year's named storms have made it to hurricane strength (five), and normally 55 - 60% of all named storms intensify to hurricane strength in the Atlantic. The rare combination of near-record ocean temperatures but unusually dry, stable air over the Atlantic is no doubt at least partially responsible for this very unusual occurrence.

Visible satellite loops show that Rina has had a respectable burst of thunderstorm activity with high, cold cloud tops this morning. This "Central Dense Overcast" (CDO) is characteristic of intensifying tropical storms that are a threat to reach hurricane strength. Rina has been bringing sporadic heavy rain squalls to the Cayman Islands over the past day; George Town on Grand Cayman Island had received 2.28" of rain and a peak wind gust of 31 mph as of 9 am EDT from the storm. Wind shear is a moderate 15 - 20 knots due to strong upper-level winds out of the southeast, and these winds are injecting dry air into Rina's southeast side, inhibiting heavy thunderstorm development there. Water temperatures are very warm, 29 - 30°C, and these warm waters extend to great depth. We don't have any surface wind reports from the vicinity of Rina; the closest buoy is Western Caribbean buoy 42057, about 60 miles east of Rina's center, which had top sustained winds out of the ESE at 29 mph this morning. We'll have to wait for the next hurricane hunter flight, scheduled for 2 pm this afternoon, to get a better idea of Rina's intensity.


Figure 1. Morning satellite image of Rina.

Forecast for Rina
The intensity forecast for Rina has a high amount of uncertainty. Rina should be able to slowly intensify through Tuesday, becoming a strong tropical storm. On Wednesday, Rina will be approaching a dry airmass with high wind shear that lies over the extreme northwestern Caribbean. Since Rina is a small storm, these hostile conditions could cause the storm to dissipate on Wednesday as it nears landfall over the Yucatan Peninsula, as predicted by the ECMWF and NOGAPS models. The completely opposite scenario is predicted by the GFDL and HWRF models, which forecast Rina will stay just south of the high shear/dry air region, and attain major hurricane status. The official NHC forecast of a Category 1 Hurricane Rina late this week is a reasonable compromise between these extremes. The track forecast for Rina also presents difficulties. A west-northwest to northwest motion towards the Yucatan Peninsula is likely through Wednesday. A trough of low pressure is predicted to pass to the north of Rina late this week, but the models are increasingly suggesting that Rina will not be far enough north to get caught up in the trough, but instead will remain trapped in the Western Caribbean. None of the latest 06Z (2 am EDT) model runs of the GFS, NOGAPS, GFDL, or HWRF models are predicting that Rina's center will make it north of Cuba during the next five days. In any case, heavy rains from Rina should begin affecting Mexico's Yucatan Peninsula, northern Belize, and extreme Western Cuba on Wednesday.

97L
A broad region of low pressure about 300 miles west of the southern Lesser Antilles Islands (Invest 97L), is moving west-northwest at 10 mph through the Caribbean Sea. This low has very limited heavy thunderstorm activity, due to dry air, and no signs of a surface circulation. NHC is giving 97L just a 10% chance of developing into a tropical depression by Wednesday. 97L is under low wind shear less than 10 knots, and this shear is expected to remain low through Thursday. By the time 97L reaches the region between Jamaica and Nicaragua in the Central Caribbean on Thursday or Friday, the storm should find a moister environment, and could develop into a tropical depression. The NOGAPS model predicts 97L could develop into a tropical depression by Saturday.

Jeff Masters

Hurricane

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Western Caribbean disturbance 96L close to tropical depression status

By: JeffMasters, 3:21 PM GMT on October 23, 2011

A region of disturbed weather in the Western Caribbean (Invest 96L) has become more organized this morning, and is close to tropical depression status. A hurricane hunter aircraft is scheduled to investigate 96L this afternoon at 2 pm EDT to see if a tropical depression has formed. The system is located just offshore from the Nicaragua/Honduras border, and is bringing heavy rains to northeastern Honduras. Visible satellite loops show that 96L is close to having a well-developed surface circulation, but the heavy thunderstorm activity is all on the west side of the center, due to a large region of dry air to the east. Wind shear is a moderate 10 - 20 knots due to strong upper-level winds out of the east, and these winds are injecting dry air into 96L's east side, keeping any heavy thunderstorms from developing on that side. Water temperatures are very warm, 29 - 30°C, and these warm waters extend to great depth.


Figure 1. Morning satellite image of 96L.

Forecast for 96L
I expect 96L will be able to organize into a tropical depression later today or on Monday, though this process will be slowed by the dry air to the storm's east, and perhaps by proximity to the land areas of Nicaragua and Honduras. NHC gave 96L a 60% chance of developing into a tropical depression by Tuesday in their 8 am Tropical Weather Outlook today. Steering currents favor a motion to the west-northwest or northwest, and it is likely that heavy rains from 96L will spread over Belize by Tuesday night, when the storm will probably be called Tropical Storm Rina. Heavy rains from the storm will spread over Mexico's Yucatan Peninsula, including Cozumel and Cancun, by Wednesday afternoon. On Wednesday, 96L will be encountering a dry airmass with high wind shear that lies over the extreme northwestern Caribbean. Since 96L is a small storm, these hostile conditions should cause the storm to weaken significantly before any potential landfall occurs.

97L
A broad region of low pressure near 11°N, 55°W, about 300 hundred miles east of the southern Lesser Antilles Islands (Invest 97L), is moving slowly west-northwest towards the Lesser Antilles. This low has very limited heavy thunderstorm activity, due to dry air. NHC is giving 97L just a 10% chance of developing into a tropical depression by Tuesday. 97L is under a moderate 10 - 20 knots of wind shear, and this shear is expected to drop to the low range, less than 10 knots, by Monday, when the storm will be in the Eastern Caribbean Sea. By the time 97L approaches Jamaica in the Central Caribbean on Friday, the storm should find a moister environment, and could develop into a tropical depression then, as predicted by the NOGAPS model.

Jeff Masters

Hurricane

Updated: 3:22 PM GMT on October 23, 2011

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Little change to 96L; El Salvador flood among its worst in history

By: JeffMasters, 2:55 PM GMT on October 22, 2011

A region of disturbed weather in the Western Caribbean (Invest 96L) is bringing heavy rains to coastal Nicaragua and Honduras, and has the potential to develop into a tropical depression Sunday or Monday. Visible satellite loops show that 96L has changed little in organization since yesterday. Some rotation is apparent, but the heavy thunderstorm activity is quite limited due to a large region of dry air to the east, as seen on water vapor satellite loops. There are no signs of a surface circulation. Surface pressures have been falling since Thursday at San Andres Island, near the center of 96L. Wind shear is a moderate 10 - 20 knots in the region, and is expected remain in the moderate range through Tuesday. Water temperatures are very warm, 29 - 30°C, and these warm waters extend to great depth.


Figure 1. Morning satellite image of 96L.

Forecast for 96L
The moderate wind shear and warm waters should allow for some development of 96L over the next few days, though this will be slowed by the dry air to the storm's east, and perhaps by proximity to the land areas of Nicaragua and Honduras. The models are less enthusiastic today about developing 96L into a tropical depression than they were yesterday. The ECMWF no longer predicts development, and the GFS and NOGAPS predict only weak development before 96L moves ashore over Honduras on Tuesday. On Wednesday, a strong trough of low pressure will be passing over the Eastern U.S., and this trough has the potential to turn 96L northwards into Western Cuba. This is more likely to happen if 96L is stronger and deeper, and thus able to "feel" the upper-level winds the trough will bring. The UKMET model predicts 96L will develop into a tropical storm that moves through the Yucatan Channel between Cuba and Mexico on Thursday. If 96L remains a weak and shallow system, though, it is more likely to stay trapped in the Western Caribbean and make landfall in Nicaragua or Honduras. NHC gave 96L a 60% chance of developing into a tropical depression by Monday in their 8 am Tropical Weather Outlook today. The hurricane hunter mission scheduled for today was cancelled due to the lack of development of 96L; the mission has been re-scheduled for Sunday afternoon.

97L
A broad region of low pressure near 10°N, 57°W, about 400 hundred miles east of Trinidad (Invest 97L), is moving slowly west-northwest towards the Lesser Antilles Islands. This low has very limited heavy thunderstorm activity, due to dry air to the northwest. NHC is giving 97L just a 10% chance of developing into a tropical depression by Monday. 97L is under a moderate 10 - 20 knots of wind shear, and this shear is expected to drop to the low range, less than 10 knots, by Monday, when the storm will be in the Eastern Caribbean Sea. By the time 97L approaches Jamaica in the Central Caribbean in 5 - 6 days, the storm should find a moister environment, and there is a chance for 97L to develop into a tropical depression, as predicted by the NOGAPS model.


Figure 2. Rainfall in El Salvador for the 10-day period ending on Friday, October 21, at 8 am EDT. At Huizucar, an astonishing 1.513 meters (4.96 feet) of rain fell during those ten days. Image credit: Hydrological Service of El Salvador.

Death toll from Central American rains rises to 105
“I want to tell the world that El Salvador is going through one of the most dramatic disasters in its history,” President Mauricio Funes said on national radio and television Wednesday night, as he appealed for international aid. A week of torrential rains across Central America have triggered extreme floods and landslides that have killed 105 people, according to media reports. El Salvador, Guatemala, Honduras and Nicaragua have declared states of emergency due to the disaster. El Salvador and Guatemala have seen the worst flooding, with 34 and 38 people killed, respectively. Another 18 have died in Honduras, 13 in Nicaragua, and 5 in Costa Rica. The rains were due to a large area of low pressure that was moistened by the landfall of Tropical Depression 12-E near the Mexico/Guatemala border last week. Contributing to the record-intensity rains were ocean temperatures off the coast of El Salvador that were 0.5 - 1°C above average during the first half of October, allowing more water vapor than usual to evaporate into the air. Over the past ten days, rainfall amounts of over a meter (39.4") have fallen over a large area of southwest El Salvador (Figure 2.) At Huizucar, an astonishing 1.513 meters (4.96 feet) of rain fell in the past ten days.

I'll have a new post on Sunday.

Jeff Masters

Flood Hurricane

Updated: 2:55 PM GMT on October 22, 2011

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Western Caribbean disturbance 96L growing more organized

By: JeffMasters, 5:14 PM GMT on October 21, 2011

A region of disturbed weather in the Western Caribbean (Invest 96L) is bringing heavy rains to coastal Nicaragua, and has the potential to develop into a tropical depression this weekend. Visible satellite loops show that 96L is beginning to show signs of organization. Some rotation is apparent, and the upper-level cirrus clouds streaming away from the center indicate that 96L is establishing an upper-level outflow channel to the east. The heavy thunderstorm activity is quite limited at present, because a large region of dry air to the east of 96L is interfering with development, as seen on water vapor satellite loops. An ASCAT pass at 11:05 am EDT showed no signs of a surface circulation, with surface winds in the 25 - 30 mph range. Surface pressures are slowly falling at San Andres Island, near the center of 96L. Wind shear is a moderate 10 - 20 knots in the region, and is expected remain in the moderate range through Monday. Water temperatures are very warm, 29 - 30°C, and these warm waters extend to great depth.


Figure 1. Afternoon satellite image of 96L.

Forecast for 96L
The moderate wind shear and warm waters should allow some modest development of 96L over the next few days, though this will be slowed by the dry air to the storm's east. The models are quite enthusiastic about developing 96L into a tropical depression, and our top four reliable models for forecasting genesis--the ECMWF, GFS, UKMET, and NOGAPS--have all been predicting formation of a tropical depression by Monday in one or more of their runs over the past day. 96L is in an area of weak steering currents, and will move little over the next three days. On Tuesday and Wednesday, a strong trough of low pressure will be passing over the Eastern U.S., and this trough has the potential to turn 96L northwards into Cuba. This is more likely to happen if 96L is stronger and deeper, and thus able to "feel" the upper-level winds the trough will bring. The 12Z run of the GFS model and 00Z runs of the ECMWF and UKMET models predict 96L will develop into a tropical storm that hits Western Cuba on Wednesday or Thursday, and potentially affecting the Cayman Islands, South Florida, and the Bahamas as well. If 96L remains a weak and shallow system, it is more likely to stay trapped in the Western Caribbean and make landfall in Nicaragua. This is the solution of the NOGAPS model, which has 96L moving ashore on Tuesday over Nicaragua as a weak system. NHC gave 96L a 30% chance of developing into a tropical depression by Sunday in their 8 am Tropical Weather Outlook. A hurricane hunter mission is scheduled to investigate 96L Saturday afternoon.

I'll have a new post on Saturday, but might wait until the afternoon, when the hurricane hunter data becomes available.

Jeff Masters

Hurricane

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NOAA winter forecast: drought in Texas, wet in the Northwest and Ohio Valley

By: JeffMasters, 4:17 PM GMT on October 20, 2011

The Southern Plains should prepare for continued drier and warmer than average weather, while the Pacific Northwest is likely to be colder and wetter than average from December through February, according to the annual Winter Outlook released October 20 by NOAA. We currently have weak La Niña conditions over the tropical Pacific ocean, which means that a large region of cooler than average waters exists along the Equator from the coast of South America to the Date Line. Cooler than average waters in this location tend to deflect the jet stream such that the Pacific Northwest experiences cooler and wetter winters than average, while the southern U.S. sees warmer and drier winter weather. NOAA's forecast calls for a typical La Niña winter over the U.S.--warm and dry over the Southern Plains, cool and wet over the Pacific Northwest, and wetter than average over the Ohio Valley. According to NOAA's latest La Niña discussion, La Niña is expected to remain solidly entrenched throughout the coming winter and into spring.



Figure 1. Forecast temperature and precipitation for the U.S. for the upcoming winter, as predicted by the Winter Outlook released October 20 by NOAA.

Grading last year's forecast
Last year, NOAA predicted: "The Pacific Northwest should brace for a colder and wetter than average winter, while most of the South and Southeast will be warmer and drier than average". This forecast did not verify for Northwest, which had a winter with near average temperatures and precipitation. The South and Southeast were indeed much drier than average, as predicted, but the Southeast was much colder than average, in contradiction to the forecast of a warm winter. Last year's winter forecast was thus was a poor one. The reason for its failure was that it only took into account the impacts of La Niña on the weather--and not the Arctic Oscillation (AO), and its close cousin, the North Atlantic Oscillation (NAO.)

What will the Arctic Oscillation and North Atlantic Oscillation do?
The North Atlantic Oscillation (NAO) is a climate pattern in the North Atlantic Ocean of fluctuations in the difference of sea-level pressure between the Icelandic Low and the Azores High. It is one of oldest known climate oscillations--seafaring Scandinavians described the pattern several centuries ago. Through east-west oscillation motions of the Icelandic Low and the Azores High,the NAO controls the strength and direction of westerly winds and storm tracks across the North Atlantic. A large difference in the pressure between Iceland and the Azores (positive NAO) leads to increased westerly winds and mild and wet winters in Europe. Positive NAO conditions also cause the Icelandic Low to draw a stronger south-westerly flow of air over eastern North America, preventing Arctic air from plunging southward. In contrast, if the difference in sea-level pressure between Iceland and the Azores is small (negative NAO), westerly winds are suppressed, allowing Arctic air to spill southwards into eastern North America more readily. This pattern is kind of like leaving the refrigerator door ajar--the Arctic refrigerator warms up, but all the cold air spills out into the house where people live. Negative NAO winters tend to bring cold winters to Europe and the Eastern U.S., and the prevailing storm track moves south towards the Mediterranean Sea. This brings increased storm activity and rainfall to southern Europe and North Africa. It should be noted that the NAO is a close cousin of the Arctic Oscillation (AO), and can be thought of as the North Atlantic component of the larger-scale Arctic Oscillation. Since the AO is a larger-scale pattern, scientists refer to the AO instead of the NAO when discussing large-scale winter circulation patterns. The winter of 2009 - 2010 had the most extreme negative NAO (and AO) since record keeping began in 1950. The NAO index was -1.67, beating the previous record of -1.47 set in the winter of 1962 - 1963. The NAO and AO were again strongly negative last winter in December and January. These negative AO conditions were responsible for unusual cold weather and snows over Eastern North America and Europe the past two winters. Unfortunately, the AO is not predictable more than about two weeks in advance. Thus, the latest NOAA winter forecast warns: “The evolving La Niña will shape this winter,” said Mike Halpert, deputy director of NOAA’s Climate Prediction Center. “There is a wild card, though. The erratic Arctic Oscillation can generate strong shifts in the climate patterns that could overwhelm or amplify La Niña’s typical impacts.”

Winter and the sunspot cycle
Another major influence on the AO and winter circulation patterns might be the 11-year solar cycle. Recent satellite measurements of ultraviolet light changes due to the 11-year sunspot cycle show that these variations are larger than was previously thought, and may have major impacts on winter circulation patterns. A climate model study published this month in Nature Geosciences by Ineson et al. concluded that during the minimum of the 11-year sunspot cycle, the sharp drop in UV light can drive a strongly negative AO pattern: "low solar activity, as observed during recent years, drives cold winters in northern Europe and the United States, and mild winters over southern Europe and Canada, with little direct change in globally averaged temperature." The winters of 2009 - 2010 and 2010 - 2011 both fit this pattern, with strongly negative AO conditions occurring during solar minimum. The coming winter of 2011 - 2012 will have a much increased level of solar activity (Figure 2), so we may speculate that a strongly negative AO and a cold winter in northern Europe and the United States is less likely.


Figure 2. The number of sunspots from 2000 - 2011 shows that solar minimum occurred in December, 2008, and that solar activity has been rising sharply in recent months. The peak of the current solar cycle is forecast to arrive in May 2013. Image credit: NOAA Space Weather Prediction Center.

How will Arctic sea ice loss affect the winter?
NOAA's annual Arctic Report Card discussed the fact that recent record sea ice loss in the summer in the Arctic is having major impacts on winter weather over the continents of the Northern Hemisphere. The Report Card states, "There continues to be significant excess heat storage in the Arctic Ocean at the end of summer due to continued near-record sea ice loss. There is evidence that the effect of higher air temperatures in the lower Arctic atmosphere in fall is contributing to changes in the atmospheric circulation in both the Arctic and northern mid-latitudes. Winter 2009 - 2010 showed a new connectivity between mid-latitude extreme cold and snowy weather events and changes in the wind patterns of the Arctic; the so-called Warm Arctic-Cold Continents pattern...With future loss of sea ice, such conditions as winter 2009 - 2010 could happen more often. Thus we have a potential climate change paradox. Rather than a general warming everywhere, the loss of sea ice and a warmer Arctic can increase the impact of the Arctic on lower latitudes, bringing colder weather to southern locations." As a specific example of what the Report Card is talking about, Francis et al. (2009) found that during 1979 - 2006, years that had unusually low summertime Arctic sea ice had a 10 - 20% reduction in the temperature difference between the Equator and North Pole. This resulted in a weaker jet stream with slower winds that lasted a full six months, through fall and winter. The weaker jet caused a weaker Aleutian Low and Icelandic Low during the winter, resulting in a more negative Arctic Oscillation (AO), allowing cold air to spill out of the Arctic and into Europe and the Eastern U.S. Thus, Arctic sea ice loss may have been partially responsible for the record negative AO observed during the winter of 2009 - 2010, and strongly negative AO last winter. If the Arctic Report Card is right, we'll be seeing more of this pattern during coming winters--possibly even during the winter of 2011 - 2012, since Arctic sea ice loss this year was virtually tied with 2007 as the greatest on record.


Figure 3. Observed temperature and precipitation departures from average during December - February for the last three winters with a La Niña event in the "weak" category: 1984 - 1985, 1995 - 1996, and 2000 - 2001. These winters tended to be much colder than average over most of the country, particularly in the Upper Midwest. Dry conditions occurred over the Southeast and Pacific coast, and wetter than average conditions in the Midwest. Image credit: NOAA/ESRL.

What happened during the last three weak La Niña winters?
The last three winters with weak La Niña conditions occurred in 2000 - 2001, 1995 - 1996, and 1984 - 1985. These winters tended to be much colder than average over most of the country, particularly in the Upper Midwest (Figure 3.) Dry conditions were observed over the Southeast and Pacific coast, and wetter than average conditions in the Midwest. The winter of 1995 - 1996 featured a strongly negative NAO, and occurred during a minimum in the solar cycle. That winter featured many cold air outbreaks across the Eastern U.S., resulting in fifteen major cities setting new all-time seasonal snowfall total, including 75.6" at New York City's Central Park. A better analogue for the coming winter may be the winter of 2000 - 2001, since that winter occurred during a peak of the solar cycle, and Arctic sea ice loss was closer to what was observed this year. The winter of 2000 - 2001 had a negative AO in December, but positive in January and February. This led to very cold conditions with heavy snows in December, and relatively mild weather in January and February. Overall, the winter of 2000 - 2001 ranks as the 27th coldest since 1895.

Summary
I'm often asked by friends and neighbors what my forecast for the coming winter is, but I usually shrug and ask them to catch some woolley bear caterpillars for me so I can count their stripes and make a random forecast. Making an accurate winter forecast is very difficult, as there is too much that we don't know. I've learned to expect the unexpected and unprecedented from our weather over the past two years, so perhaps the most unexpected thing would be a very average winter for temperatures. The one portion of the winter forecast that does have a high probability of being correct, though, is the forecast of dry conditions over Texas and surrounding states. Extreme droughts tend to be self-reinforcing, by creating high pressure zones around them that tend to deflect rain-bearing low pressures systems. The unpredictable AO doesn't affect weather patterns that much over Texas, so we can expect that the fairly predictable drying La Niña influence will dominate Texas' weather this winter.

For more information
Golden Gate Weather has a nice set of imagery showing historic La Niña winter impacts, based on whether it was a "weak", "moderate", or "strong" event.

Francis, J. A., W. Chan, D. J. Leathers, J. R. Miller, and D. E. Veron, 2009: Winter northern hemisphere weather patterns remember summer Arctic sea-ice extent. Geophys. Res. Lett., 36, L07503, doi:10.1029/2009GL037274.

Honda, M., J. Inoue, and S. Yamane, 2009: Influence of low Arctic sea-ice minima on anomalously cold Eurasian winters. Geophys. Res. Lett., 36, L08707, doi:10.1029/2008GL037079.

Ineson, S., et al., 2011, Solar forcing of winter climate variability in the Northern Hemisphere, Nature Geoscience (2011) doi:10.1038/ngeo1282

Overland, J. E., and M. Wang, 2010: Large-scale atmospheric circulation changes associated with the recent loss of Arctic sea ice. Tellus, 62A, 1.9.

Petoukhov, V., and V. Semenov, 2010: A link between reduced Barents-Kara sea ice and cold winter extremes over northern continents. J. Geophys. Res.-Atmos., ISSN 0148-0227.

Seager, R., Y. Kushnir, J. Nakamura, M. Ting, and N. Naik (2010), Northern Hemisphere winter snow anomalies: ENSO, NAO and the winter of 2009/10, Geophys. Res. Lett., 37, L14703, doi:10.1029/2010GL043830.

A Western Caribbean disturbance worth watching
A large area of disturbed weather in the Western Caribbean is bringing heavy rains to coastal Nicaragua and Honduras. The heavy thunderstorms are in an area of weak steering currents, and will move little over the next two days. Wind shear is a high 20 - 30 knots in the region, but is expected to drop to the moderate range on Friday, and remain moderate through the weekend. This should allow some slow development of the disturbance, and the GFS, UKMET, and NOGAPS models all develop the disturbance into a tropical depression by Monday. The most likely areas to be affected by this hypothetical storm are Honduras and Nicaragua, but we can't rule out a scenario where the storm moves northwards and threatens Cuba late next week, as the UKMET model is predicting. NHC gave the disturbance a 10% chance of developing into a tropical depression by Sunday in their 8 am Tropical Weather Outlook.

Another area of disturbed weather near 12N 47W, midway between Africa and the Lesser Antilles islands, is also being given a 10% of development by NHC. This disturbance has a respectable amount of spin, but the heavy thunderstorm activity is minimal. The disturbance is under a moderate 10 - 20 knots of wind shear. None of the models develops the disturbance, and recent satellite images show that the disturbance appears to be getting sheared apart. I doubt this disturbance will be around on Friday.

If there's not much change to the forecast for these disturbances on Friday, I'll leave the current post up until Saturday.

Jeff Masters

Winter Weather

Updated: 9:13 PM GMT on October 20, 2011

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September the globe's 8th warmest on record; heavy rains hit Florida

By: JeffMasters, 1:41 PM GMT on October 19, 2011

September 2011 was the globe's 8th warmest September on record, according to the National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center (NCDC). NASA's Goddard Institute for Space Studies rated September the 9th warmest on record. NASA rates the top ten warmest Septembers since 1880 as having all occurred in the past ten years. September 2011 global land temperatures were the 4th warmest on record, and ocean temperatures were the 14th warmest on record for the month of September. Global satellite-measured temperatures for the lowest 8 km of the atmosphere were above average, the 8th or 5th warmest in the 34-year record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH).


Figure 1. Departure of temperature from average for September 2011. Image credit: National Climatic Data Center (NCDC).

21st warmest September for the U.S.
September 2011 in the U.S. was the 21st warmest in the 117-year period of record, according to the National Climatic Data Center. Thirteen states in the West and Northeast had top-ten warmest Septembers on record, and one state, Mississippi, had a top-ten coolest September. On September 4th, Tropical Storm Lee made landfall on the Gulf Coast, and brought torrential rain to most of the eastern United States. While Lee brought drought relief for the Gulf Coast, it caused major flooding in the already-saturated Northeast. Rainfall totals of at least 10 inches were common along Lee's path. Eleven states from Louisiana to New York experienced a top-ten wettest September, and it was the wettest September in Pennsylvania's history. In Binghamton, New York, Lee aided in breaking three all-time precipitation records: most rainfall in a year (57.85 inches to date), most rainfall in any month (16.58 inches), and most rainfall on any calendar day (7.49 inches on September 7th). Dayton, Ohio and Allentown, Pennsylvania both had their wettest September on record. In contrast, five states had a top-ten driest September. Ten percent of the United States was in an exceptional drought--the most extreme classification--in September. Austin, Texas saw its driest September on record, receiving only 0.01 inches of rain during the month.

Weak La Niña conditions continue
La Niña continues in the equatorial Pacific, where sea surface temperatures remain 0.5°C to 1.0°C below average, qualifying this as a weak La Niña event. During the coming winter, La Niña is likely to bring drought in the South, especially to Texas. Above average temperatures can also be expected in the South. The Pacific Northwest can expect cooler than average temperatures, as well as the potential for another record-breaking winter of snowpack across the western United States. La Niña also tends to bring wetter than average conditions to the Ohio Valley.

Arctic sea ice extent second lowest on record
Arctic sea ice extent was at its second lowest on record in September, behind 2007, according to the National Snow and Ice Data Center. The center said that on September 9th, the Arctic reached its annual minimum extent, which was also the second-smallest minimum extent on record. Sea ice records date back to 1979.

Wunderground's weather historian Christopher C. Burt has an in-depth analysis of some of the more notable September global extremes in h is latest post.


Figure 2. Radar-estimated rainfall for the 24 hours ending at 9:20 am EDT over South Florida. Heavy rains of up to 5 inches affected the coast near Naples and portions of the Keys.

Heavy rains continue over South Florida
Heavy rains continue over South Florida due to the lingering remnants of Invest 95L. Key West Naval Air Facility has picked up an additional 4.61" of rain as of 9 am EDT this morning, bringing their 5-day total to 17.42" of rain. Yesterday, 95L spawned three tornadoes over Southeast Florida. One twister damaged 40 homes near Lakeport, and roofs were torn off homes in Sunrise. No injuries were reported from the tornadoes. The severe threat shifts to coastal North Carolina today, and NOAA's Storm Prediction Center has placed much of coastal North Carolina and Virginia in their "slight risk" area for severe weather.

None of the computer models predicts tropical storm formation in the Atlantic during the coming seven days. The Western Caribbean is expected to see an increase in moisture late next week and the possible formation of a strong tropical disturbance capable of bringing heavy rains.

My next post will be early Thursday afternoon, after NOAA issues their winter outlook at 11 am EDT that day.

Jeff Masters and Angela Fritz

Climate Summaries Hurricane

Updated: 1:41 PM GMT on October 19, 2011

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95L drenches Florida; floods kill 84 in Central America; huge dust storm hits TX

By: JeffMasters, 1:43 PM GMT on October 18, 2011

A large low pressure system off the Florida Gulf Coast, Invest 95L, is bringing heavy rains to Southwest Florida. Rainfall amounts in excess of 3 inches have been common across South Florida since Saturday; Miami has picked up 3.80" as of 9 am EDT this morning, and Key West Naval Air Facility has recorded 14.41", and 14.78" fell on Sugarloaf Key. Key West has experienced other rain events with far more precipitation; their all-time 24-hour rainfall is 23.28", set on November 11, 1980. Interestingly, this is more rain than fell in the entire year of 1974, when Key West received only 19.99".

Rains of 5 - 10 inches have fallen over much of the Florida Keys and Central Cuba since Sunday, according to radar rainfall estimates from the Key West Radar. Long-range radar out of Key West shows that the rain has now pushed north of the Keys, and the region between Naples and Fort Myers is getting the heaviest rains. Satellite loops show that 95L has a respectable amount of heavy thunderstorm activity, but the system is disorganized and has been stretched by wind shear. With wind shear now a high 20 - 30 knots over 95L, development is unlikely, and NHC has dropped their odds of it developing into a tropical depression to 10%. 95L will bring heavy rains of 2 - 3 inches to Southwest Florida today, and NOAA's Storm Prediction Center has placed much of Florida in their "slight risk" area for severe weather, including the possibility of isolated tornadoes.


Figure 1. True-color MODIS image of an interesting 50 km-wide vortex near the north coast of Mexico's Yucatan Peninsula that became the center of 95L late yesterday afternoon. Image taken at 1:45 pm EDT October 17, 2011. Image credit: NASA.

Heavy rains kill 84 in Central America
A week of torrential rains across Central America have triggered extreme floods and landslides that have killed 84 people, with 9 missing, according to media reports. El Salvador and Guatemala have seen the worst flooding, with 32 and 31 people killed, respectively. Another 13 have died in Honduras, and 8 in Nicaragua. The rains were due to a large area of low pressure that was moistened by the landfall of Tropical Depression 12-E near the Mexico/Guatemala border last week. Since the beginning of October, the region near the coast on the Guatemala/El Salvador border has received over 800 mm (31.50") of rain, according to Norman Avila of climaya.com, a Guatemalan weather web site.


Figure 2. Visible satellite animation of the Texas South Plains dust storm of October 17, 2011. Image credit: NWS Lubbock.

Massive dust storm sweeps through the Texas Panhandle
It was a very bad afternoon rush hour yesterday in the Texas Panhandle. A powerful cold front pushed through the state during the afternoon, and damaging north winds behind the front whipped up a dangerous dust storm that cut visibility to near-zero during the afternoon rush hour. Lubbock recorded sustained winds of 48 mph, gusting to 63 mph, with a visibility of 0.2 miles in heavy dust at 5:36 pm CDT. The dust storm was reminiscent of the great dust storms of the 1930s dust bowl era, and was due to the ongoing exceptional drought. Unfortunately, the front brought no rain to the area, and Lubbock has received just 3.16" of rain so far in 2011--more than 13.50" below average. In his Climate Abyss blog, Texas's state climatologist, John Nielsen-Gammon, gives a 25% that the current drought will last five more years. He has an interesting post on how global warming may have affected the drought. He concludes:

Precipitation: The balance of evidence does not support the assertion that the rainfall deficit since October 2010 was made larger or more likely by global warming.

Temperature: Compared to long-term averages of summer temperature, the rainfall deficit accounted for about 4°F of excess heat and global warming accounted for about 1°F of excess heat. Warmer temperatures lead to greater water demand, faster evaporation, and greater drying-out of potential fuels for fire. Thus, the impacts of the drought were enhanced by global warming, much of which has been caused by man.


Video 1. Video of the October 17, 2011 dust storm in Lubbock, Texas.

Jeff Masters

Dust Storm Flood Hurricane

Updated: 11:10 PM GMT on October 18, 2011

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95L drenching the Keys, could develop into a tropical depression

By: JeffMasters, 2:12 PM GMT on October 17, 2011

A large low pressure system centered about 100 miles north of Mexico's Yucatan peninsula, Invest 95L, is bringing heavy rains to Western Cuba and South Florida. Rainfall amounts in excess of 3 inches have been common across South Florida since Saturday; Miami has picked up 3.40" as of 10 am EDT this morning, and Key West Naval Air Facility recorded 9.72". Rains of 5 - 8 inches have fallen over much of the Florida Keys and Central Cuba since Sunday, according to radar rainfall estimates from the Key West Radar. Long-range radar out of Key West shows rain is affecting most of South Florida south of Fort Myers, but there is no obvious spin to the echoes, and no evidence of organized spiral bands forming. Satellite loops show that 95L has a respectable amount of heavy thunderstorm activity that is increasing in areal coverage. There is no evidence of a well-formed surface circulation trying to develop, though surface observations in the Western Caribbean do show that 95L has a broad counter-clockwise circulation. Two ships to the north of 95L's center measured sustained winds in excess of 30 mph this morning, but no land stations are reporting sustained winds over 30 mph. Water temperatures over the regions are near 29°C, which is plenty warm to support a tropical storm.


Figure 1. Morning satellite image of Invest 95L.


Figure 2. Predicted rainfall for the 5-day period ending 8 am Saturday October 22, 2011. Image credit: NOAA/HPC.

Wind shear over 95L is currently a moderate 10 - 20 knots, and is expected to stay in the moderate range through Tuesday night. NHC is giving the system a 60% chance of developing into a tropical depression by Wednesday, and has scheduled a hurricane hunter aircraft to investigate the system this afternoon at 2 pm EDT. The models are generally showing only weak development of 95L. The storm is currently moving north at 5 - 10 mph, but should turn to the northeast by Tuesday afternoon, as it gets caught up by an approaching trough of low pressure. This trough should pull 95L into the west coast of Florida on Tuesday night or Wednesday morning between Fort Myers and St. Marks. Portions of southwest Florida could receive up to 5 inches of rain from 95L; locations to the north of Tampa will less rain, due to the large amount of dry air over the northern Gulf of Mexico that will affect the northwestern portion of the storm. Once 95L meets up with the trough, wind shear will rise sharply, and it is unlikely 95L will be able to grow any stronger than a 50 mph tropical storm before landfall occurs. It is more likely that 95L will have top winds of 35 - 45 mph Tuesday night near the time of landfall.

Another area of disturbed weather in the Eastern Atlantic, 1400 miles east of the Lesser Antilles Islands, has developed a modest degree of spin, but has very limited heavy thunderstorm activity. NHC is giving this system a 10% chance of developing into a tropical depression by Wednesday.

Jeff Masters

Hurricane

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95L could develop into a depression and affect Western Florida

By: JeffMasters, 4:17 PM GMT on October 16, 2011

A large low pressure system centered over the eastern Yucatan peninsula, near Mexico's Cozumel Island (Invest 95L), is bringing heavy rains to Western Cuba and the Yucatan Peninsula. Rainfall amounts of 5 - 10 inches have fallen over Central and Western Cuba since October 9, according to radar rainfall estimates from the Key West Radar. Heavy rains have also affected portions of the Florida Keys; a personal weather station on Plantation Key recorded 2.28" of rain so far this weekend. Satellite loops show that 95L does not have a well-formed surface circulation, but the storm does have a respectable amount of heavy thunderstorm activity that is increasing in intensity and areal coverage. Surface observations in the Western Caribbean reveal that 95L has a broad counter-clockwise circulation. A ship in the Yucatan Channel recorded sustained winds of 44 mph this morning, and another ship measured sustained winds of 39 mph about 30 miles southwest of Key West, but no land stations are reporting winds over 30 mph. Water temperatures over the regions are near 29°C, which is plenty warm to support a tropical storm.


Figure 1. Afternoon satellite image of Invest 95L.

Wind shear over 95L is currently a moderate 10 - 20 knots, and is expected to stay in the moderate range over the next three days. This should allow 95L a decent chance to develop into a tropical depression, once it pulls away from the Yucatan Peninsula on Monday. NHC is giving the system a 50% chance of developing into a tropical depression by Tuesday, and has scheduled a hurricane hunter aircraft to investigate the system on Monday afternoon. I'd put the odds of development higher, at 70%. All of the models are showing only weak development of 95L. The storm is currently moving northwest, but should turn north and then northeast by Tuesday, as it gets sucked into an approaching trough of low pressure. This trough should pull 95L into the west coast of Florida on Tuesday, and the southwest portion of Florida could receive up to 6 inches of rain from 95L. Once 95L meets up with the trough, wind shear will rise sharply, and it is unlikely 95L will be able to grow any stronger than a 50 mph tropical storm before landfall occurs along the west coast of Florida. It is more likely that 95L will have top winds of 35 - 45 mph at landfall on Tuesday.

Another area of disturbed weather in the Eastern Atlantic, 1500 miles east of the Lesser Antilles Islands, has developed a modest degree of spin, but has very limited heavy thunderstorm activity. NHC is giving this system a 10% chance of developing into a tropical depression by Tuesday.

Jeff Masters

Updated: 4:18 PM GMT on October 16, 2011

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Western Caribbean disturbance bringing heavy rains

By: JeffMasters, 3:02 PM GMT on October 15, 2011

In the Western Caribbean, a large area of disturbed weather associated with a low pressure system is bringing heavy rains to Western and Central Cuba, the Cayman Islands, and Mexico's Yucatan Peninsula. Moisture from Tropical Depression 12-E, which moved inland near the Mexico/Guatemala border and dissipated on Wednesday, has invigorated this low. Rainfall amounts of 5 - 10 inches have fallen over Central Cuba since October 9, according to radar estimates from the Key West Radar.


Figure 1. Morning radar image from Key West, FL radar.

The low is too large to develop quickly, and is likely to move over the Yucatan Peninsula on Sunday, limiting the potential for development. NHC is giving the system just a 20% chance of developing into a tropical depression by Monday. Most of the models predict only weak development of the storm, since wind shear is currently a moderate to high 15 - 25 knots, and is expected to be in the moderate to high range over the next three days. The low is likely to move north and then northeast early next week, and cross the west coast of Florida on Tuesday or Wednesday. Rains from the storm are already affecting the Florida Keys, as seen on long-range Key West radar. Mexico's Yucatan Peninsula and Western Cuba will see the heaviest rains from the disturbance over the weekend, and extreme South Florida and the Florida Keys could see heavy rains of 3 - 5 inches through Monday.

Another area of disturbed weather over the far Eastern Atlantic, 700 miles southwest of the Cape Verde Islands, has developed a modest degree of spin, but has very limited heavy thunderstorm activity. NHC is giving this system a 20% chance of developing into a tropical depression by Monday.

Jeff Masters

Hurricane

Updated: 7:32 PM GMT on January 05, 2012

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Thailand flood its most expensive in history; Western Caribbean disturbance develops

By: JeffMasters, 2:03 PM GMT on October 14, 2011

Heavy rains in Thailand during September and October have led to extreme flooding that has killed 283 people and caused that nation's most expensive natural disaster in history. On Tuesday, Thailand's finance minister put the damage from the floods at $3.9 billion. This makes the floods of 2011 the most expensive disaster in Thai history, surpassing the $1.3 billion price tag of the November 27, 1993 flood, according to the Centre for Research on the Epidemiology of Disasters (CRED). Floodwaters have swamped fields and cities in 61 of Thailand's 77 provinces, affected 8.2 million people, and damaged approximately 10% of the nation's rice crop. Thailand is the world's largest exporter of rice, so the disaster may put further upward pressure on world food prices, which are already at the highest levels since the late 1970s. Some of the highest tides of the month occur this weekend in the capital of Bangkok, and the additional pressure that incoming salt water puts on the flood walls protecting the city is a major concern. A moderate monsoon flow continues over Southeast Asia, and the latest GFS model precipitation forecast foresees an additional 2 - 5 inches of rain over most of Thailand during the next three days.


Figure 1. Thailand's Chao Phraya River forms at the confluence of smaller rivers near Nakhon Sawan and flows past Bangkok to the Gulf of Thailand. Floodwalls meant to contain the river collapsed in downtown Nakhon Sawan, the Bangkok Post reported on October 11, 2011. The aftermath of the burst floodwalls left the city looking like a lake. As rivers overflowed in Thailand, the Tônlé Sab (Tonle Sap) lake in neighboring Cambodia (lower right of images) overflowed. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite captured these images on October 11, 2011, and October 8, 2010. These images use a combination of visible and infrared light to better distinguish between water and land. Vegetation is green, and clouds are pale blue-green. Water is dark blue. In 2011, water rests on floodplains between Phitsanulok and Nakhon Sawan. Image credit: NASA.

Heavy rains due to an active monsoon and moisture from tropical cyclones
Rainfall in September peaked at 574.3mm (22.61") at Nong Kai in Northeastern Thailand, 501mm (19.72") at Uttardit in Northern Thailand, and 1446.7mm (56.96") in Eastern Thailand. For these regions, precipitation averaged 40 - 46% above normal in September. In the week ending Oct. 13, an additional 4 - 8" fell in Central and Thailand, where the capital of Bangkok lies. On Thursday, 38 mm (1.53") fell in Bangkok, and rainfall amounts of 1 - 3" fell over much of Central Thailand. Heavy monsoon rains are common in Thailand and Southeast Asia during La Niña events, and we currently have a weak La Niña event occurring. Ocean temperatures in the waters surrounding Thailand during September and October have been approximately 0.3°C above average, which has increased rainfall amounts by putting more water vapor into the air. The remains of Tropical Storm Haitang and Typhoon Nesat also brought heavy rains in late September. The flooding has also affected neighboring Cambodia, killing at least 183 people. Floods have also killed 18 in Vietnam and 30 in Laos this fall.

The Atlantic.com has some remarkable photos of the flooding in Thailand.


Figure 2. Top ten most expensive natural disasters in Thailand since 1900, as tabulated by the Centre for Research on the Epidemiology of Disasters (CRED). This month's disaster (number one on the table above) is not yet in the CRED data base.

Hurricane Jova kills five in Mexico, but damage limited
Hurricane Jova killed five people in Mexico but damage was less than expected, amounting to less than $52 million, according to AIR-Worldwide. Jova hit the Pacific coast of Mexico Tuesday night as a Category 2 hurricane with 100 mph winds. Wunderblogger Mike Theiss rode out the storm on the coast, and has a a great post on his experience, which I excerpt here: "the winds suddenly picked up fiercely and started pounding the building I took shelter in. The surf ran way up on the beach and the waves were pounding the buildings and spraying up over everything at the pool. The wind was screaming and howling and the glass was flying. The Spanish tiles were getting ripped off the roof and all the glass light fixture were popping like balloons."


Figure 3. Mudslide from Hurricane Jova covers a road near Mazanillo, Mexico. Image credit: Mike Theiss.

Invest 94L in the Atlantic no threat
An area of disturbed weather (Invest 94L) between North Carolina and Bermuda is moving quickly to the northeast at 15 - 20 mph. This system has a modest amount of heavy thunderstorm activity and a the beginnings of a surface circulation, as seen on recent visible satellite imagery. Conditions are marginal for this to develop into a tropical depression, as wind shear is a high 20 - 30 knots, and ocean temperatures are at the lower limit for develoment, 26.5°C (80°F.) NHC is giving 94L a 20% chance of developing.

Western Caribbean disturbance
In the Western Caribbean, a large area of disturbed weather associated with a low pressure system has developed. Moisture from Tropical Depression 12-E, which moved inland near the Mexico/Guatemala border and dissipated on Wednesday, is invigorating the Western Caribbean low. Heavy rains from the low are affecting much of Central America, Cuba, and Mexico's Yucatan Peninsula, and these rains will probably intensify over the weekend as the low moves slowly northwest and gradually develops. The low is too large to develop quickly, and NHC is giving the system just a 20% chance of developing into a tropical depression by Sunday. Most of the models predict only weak development of the storm, since wind shear is currently a high 20 - 25 knots, and is expected to be in the moderate to high range, 15 - 25 knots, over the next three days. Rains from the storm are already affecting the Florida Keys, as seen on long-range Key West radar. A personal weather station on Grand Cayman Island has picked up 0.87" of rain so far this morning from the storm. Mexico's Yucatan Peninsula and Western Cuba will see the heaviest rains from the disturbance over the weekend, and South Florida could see heavy rains of 2 - 4 inches on Sunday and Monday.

Jeff Masters

Flood Hurricane

Updated: 3:23 PM GMT on October 21, 2011

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Jova and TD-12E kill 18 in Mexico, Guatemala

By: JeffMasters, 10:18 AM GMT on October 13, 2011

Hurricane Jova has dissipated, but its remnants continues to dump heavy rains over Mexico's coastal mountains near Puerto Vallarta. Jova made landfall on Mexico's Pacific coast at 10 pm PDT Tuesday night as a Category 2 storm with 100 mph winds, and was the strongest hurricane to hit Mexico's Pacific coast since Hurricane Jimena hit Baja as a Category 2 storm with 105 mph winds in 2009. Jova's torrential rains triggered flooding and mudslides that have killed five people so far in Mexico. Jova's highest rainfall amounts on Tuesday occurred in Coquimatlan, located in the state of Colima, about 30 miles northeast of Manzanillo. Coquimatlan recorded 374.4 mm (14.74") of rain on Tuesday, according to the Mexican weather service. This is not far below the all-time record hurricane rainfall for Colima state, which is 15.57", set in 1998 during Hurricane Javier.

Another significant rainfall threat is the remains Tropical Depression 12-E, which moved inland near the Mexico/Guatemala border yesterday afternoon. TD-12E is being blamed for the deaths of thirteen people in Guatemala, due to flooding, mudslides, and electrocutions from downed power lines. Tropical Depression Irwin, which is headed eastwards towards the same stretch of Mexican coast Jova affected, is expected to dissipate before reaching the coast. It is unlikely Irwin will bring significant rains to Mexico.


Figure 1. True-color MODIS image of Tropical Storm Jova (upper right) and Tropical Storm Irwin (lower left) taken at 1:30 pm EDT October 12, 2011. At the time, Jova had 65 mph winds, and Irwin had 40 mph winds. Image credit: NASA.

Wunderblogger Mike Theiss is in Barra de Navidad, just north-west of Manzanillo, and received a direct hit from Jova's eye. His final report; "Found a small building north of La Manzanilla directly in path of Hurricane Jova's eye. No power, only iPhone battery and still cell service for now. We will get a direct hit here but no lights to see anything to film. Waves are large and crashing on building. Only going to get worse !! Sorry no photos yet, today was actually nice all day and right at dark wind picked up and knocked out power."

Quiet in the Atlantic
Many of the computer models continue to predict that a strong tropical disturbance capable of becoming a tropical depression could form in the Western Caribbean or extreme southern Gulf of Mexico early next week. Some of the spin and moisture for this storm could come from the remains of TD 12-E.

Jeff Masters

Hurricane

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Category 2 Hurricane Jova hits Mexico

By: JeffMasters, 1:43 PM GMT on October 12, 2011

Hurricane Jova slowly moved ashore over Mexico's Pacific coast at 10 pm PDT last night as a Category 2 storm with 100 mph winds. Jova was the strongest hurricane to hit Mexico's Pacific coast since Hurricane Jimena hit Baja as a Category 2 storm with 105 mph winds in 2009. Jova was a small storm at landfall, with hurricane-force winds that extended outwards only 15 miles from the center. Thus, only a relatively small stretch of coast saw Jova's most dangerous winds and storm surge. A much greater concern are Jova's rains. Satellite rainfall estimates indicate that Jova had already dumped up to six inches of rain along the coast as of 2 am EDT this morning. Jova is moving very slowly and is expected to stall out over the coast on Thursday, which will lead to extremely heavy rains over the coastal mountains of Mexico. These rains are likely to accumulate to over fifteen inches in some spots, and life-threatening flash flooding and mudslides are likely in the region of Mexico between Manzanillo and Puerto Vallarta over the next three days. Recent satellite loops show the hurricane has weakened drastically since landfall, with the eye no longer apparent and much less vigorous heavy thunderstorm activity. Jova will likely weaken to a tropical storm later today.

This year's Eastern Pacific hurricane season has been below average for number of named storms, which is typical for a La Niña year. However, an unusual number of the named storms have become hurricanes and intense hurricanes--the reverse of the situation in the Atlantic. So far in 2011, there have been 10 named storms, 9 hurricanes, 5 major hurricanes, and an Accumulated Cyclone Energy (ACE) index of 108 in the Eastern Pacific. An average year should have had 13 named storms, 7 hurricanes, 3 major hurricanes, and an ACE index of 125 by October 12. On average, the Eastern Pacific sees just two more named storms and one hurricane after October 11.


Figure 1. True-color MODIS image of Jova taken at 3:55 pm EDT October 11, 2011. At the time, Jova was a Category 2 hurricane with 100 mph winds. Image credit: NASA.


Figure 2. Rainfall forecast for Hurricane Jova from this morning's 2 am EDT run of the GFDL model. Image credit: Morris Bender, NOAA/GFDL.

Links to follow Jova
Wunderblogger Mike Theiss is in Barra de Navidad, just north-west of Manzanillo, and received a direct hit from Jova's eye last night. His final report; "Found a small building north of La Manzanilla directly in path of Hurricane Jova's eye. No power, only iPhone battery and still cell service for now. We will get a direct hit here but no lights to see anything to film. Waves are large and crashing on building. Only going to get worse !! Sorry no photos yet, today was actually nice all day and right at dark wind picked up and knocked out power."

Puerto Vallarta webcam

Tropical Storm Irwin not expected to threaten Mexico
Tropical Storm Irwin, which is headed eastwards towards the same stretch of Mexican coast Jova is affecting, is expected to dissipate before reaching the coast. It is unlikely Irwin will bring significant rains to Mexico.

Quiet in the Atlantic
Many of the computer models continue to predict that a strong tropical disturbance capable of becoming a tropical depression could form in the Western Caribbean or extreme southern Gulf of Mexico early next week. Some of the spin and moisture for this storm could potentially come from Tropical Depression 12-E, which formed in the Eastern Pacific this morning, just offshore of the Mexico/Guatemala border. TD 12-E is expected to move inland over Southeast Mexico and Guatemala over the next few days, bringing very heavy rains of 5 - 10 inches capable of causing life-threatening flash flooding and mudslides.

Jeff Masters

Hurricane

Updated: 1:44 PM GMT on October 12, 2011

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Powerful Category 3 Hurricane Jova nears landfall in Mexico

By: JeffMasters, 1:42 PM GMT on October 11, 2011

Rain bands from powerful Category 3 Hurricane Jova are already deluging the southwest coast of Mexico as the storm heads towards landfall late this afternoon between Manzanillo and Puerto Vallarta. Recent satellite loops show the hurricane has weakened since yesterday afternoon, with the eye no longer visible and the cloud pattern no longer as symmetric. Moderate wind shear of 15 - 20 knots due to strong upper-level winds out of the southeast managed to inject some dry air into the core of Jova that disrupted the storm's eyewall, and it is unlikely the hurricane will be able to intensify beyond its current 115 mph strength before landfall. It is more likely that Jova will weaken as it approaches land, due to the storm's small size, which makes is vulnerable to disruption when the outer portion of the circulation hits the mountains along the Mexican coast. If Jova maintains its Category 3 strength until landfall, it will rank as one of the ten most intense Pacific hurricanes to hit Mexico since record keeping began in 1949, according to a comprehensive list of Eastern Pacific hurricane landfalls at Wikipedia. However, I expect Jova's interaction with the high mountains of Mexico will knock it down to a Category 2 storm with 100 - 105 mph winds by landfall. Hurricane-force winds extend outwards only 15 miles from the center of Jova, so a relatively small stretch of moderately to lightly-populated stretch of coast will see Jova's high winds and dangerous storm surge. A much larger swath of Mexico will see very heavy rains of 6 - 12 inches, and these rains are the primary threat from the hurricane.

The shape of the coast near Puerto Vallarta makes it difficult for a high storm surge to affect that city. Jova is passing far enough to the east of Puerto Vallarta that the winds in the Bay should be capable of elevating a surge to a height of just 1 - 2 feet above normal water levels, with perhaps a slight chance of a surge as high as 3 feet affecting the city. However, there will be high battering waves on top of the storm surge, and these waves may cause damage to ocean front property. I was in Puerto Vallarta during Hurricane Paine of 1986, and while we didn't see much of a storm surge, the coast experienced 10-foot waves that tore apart the sea wall protecting the swimming pool of the hotel I was staying at. The highest storm tide from Jova should occur near 9:55am CDT Wednesday morning, which is the time of high tide. Jova will be at its closest to Puerto Vallarta then, and is likely to be a strong tropical storm with 60 mph winds.


Figure 1. True-color MODIS image of Jova taken at 1:40 pm EDT October 10, 2011. At the time, Jova was a Category 3 hurricane with 125 mph winds. Image credit: NASA.


Figure 2. Rainfall forecast for Hurricane Jova from this morning's 2 am EDT run of the GFDL model. Image credit: Morris Bender, NOAA/GFDL.

Links to follow Jova
Wunderblogger Mike Theiss is in Barra de Navidad, just north-west of Manzanillo, and will be giving us live blogs and photos from the landfall of Jova, as his power and Internet connections permit.

Manzanillo weather

>Puerto Vallarta webcam

Tropical Depression Irwin also headed for Mexico
Once Jova has made landfall, Tropical Depression Irwin, farther to the west, may also be a concern. The computer forecast models show that late this week, Irwin will approach the same stretch of Mexican coast Jova is affecting. However, Irwin is a weak storm that is may not survive, due to high wind shear, and may end up not bringing significant rains to Mexico.

Quiet in the Atlantic
There are currently no threat areas in the Atlantic, now that Invest 93L has moved ashore over the Southeast U.S. Invest 93L did have tropical storm force winds, and will be re-analyzed in the off-season by NHC to see if it did indeed have enough organization to qualify as an unnamed subtropical storm.

The ECMWF and NOGAPS models continue to predict that a strong tropical disturbance capable of becoming a tropical depression could form in the Western Caribbean early next week. Some of the spin and moisture for this storm could potentially come from an area of disturbed weather in the Eastern Pacific, (Invest 99E), that is currently just offshore of the Mexico/Guatemala border. Invest 99E is expected to move inland over Central America over the next few days, bringing very heavy rains capable of causing flash flooding and mudslides to Southeast Mexico, Guatemala, and El Salvador.

Jeff Masters

Hurricane

Updated: 7:32 PM GMT on October 11, 2011

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Dangerous Jova approaching Mexico; welcome rains hit Texas

By: JeffMasters, 1:54 PM GMT on October 10, 2011

In the Eastern Pacific off the coast of Mexico, Hurricane Jova continues to intensify. Recent satellite loops show the hurricane has developed a prominent eye with very cold cloud tops. A hurricane hunter aircraft is scheduled to arrive at Jova near 11 am PDT today. The computer models are in good agreement that Jova will turn northeast and then north on Tuesday, with storm expected to hit near Manzanillo on Mexico's southwest coast Tuesday afternoon. The intensity forecast also appears relatively straightforward. Jova is under moderate wind shear of 10 - 15 knots, and shear is predicted to stay in the moderate range between now and landfall. Ocean temperatures are warm, 28 - 29°C, and Jova is now approaching a region where these warm waters extend to great depth, which should allow the storm to maintain major hurricane strength until landfall. The GFDL model predicts Jova will be a Category 3 at landfall on Tuesday afternoon, while the HWRF model predicts Category 4 strength. The hurricane is likely to undergo the usual fluctuations in intensity due to eyewall replacement cycles major hurricanes typically experience at this stage of their lifetimes, so Mexico will have to hope it catches Jova on one of the downswings of this cycle. If Jova maintains its current central pressure of 960 mb until landfall, it will rank as one of the ten most intense Pacific hurricanes to hit Mexico since record keeping began in 1949. According to a comprehensive list of Eastern Pacific hurricane landfalls at Wikipedia, only seven hurricanes with a central pressure of 960 mb or lower have hit Mexico's Pacific coast since 1949. Jova is a modest-sized hurricane, with hurricane-force winds that extend out only 15 miles from the center. A relatively small stretch of moderately to lightly-populated coast will see Jova's high eyewall winds and very dangerous storm surge. A much larger swath of Mexico will see very heavy rains of 5 - 10 inches, and these rains are capable of causing high loss of life due to heavy flooding and mudslides.


Figure 1. Rainfall forecast for Hurricane Jova from this morning's 2 am EDT run of the GFDL model. Image credit: Morris Bender, NOAA/GFDL.

Tropical Storm Irwin also headed for Mexico
Once Jova has made landfall, Tropical Storm Irwin, farther to the west, may also be a concern. The computer forecast models show Irwin could make landfall as a tropical storm on the Mexican coast late in the week, along the same stretch of coast Jova will affect. However, Irwin is a weak storm that is expected to weaken further as it approaches the coast, due to high wind shear, and Irwin may end up not being a significant threat to Mexico.

93L bringing heavy rains, high winds, and a tornado threat to the Southeast U.S.
A large extratropical low pressure system with heavy rain and gale-force winds (Invest 93L), is centered over Northern Florida. Water vapor satellite loops show that the center of this low is filled with dry air, and 93L is headed northwest at 5 - 10 mph. The west side of this low also has a large amount of dry air, which is limiting precipitation amounts along the Gulf of Mexico coast, but the east side has plenty of tropical moisture. Radar-estimated rainfall amounts since Friday are already in excess of ten inches just inland along the Central Florida coast. Melbourne, Florida had its second wettest October day in its history on Saturday, with 5.68" of rain. Much of coast of Northern Florida, Southern South Carolina, and Georgia, including Brunswick, are under a flood watch, high surf advisories, tornado watch, and a high wind watch for wind gusts up to 55 mph. Winds offshore the Southeast Coast are not quite as strong as last night, when tropical storm force winds occurred along the Central Florida coast. Buoy 41009 offshore from Cape Canaveral recorded sustained winds of 52 mph, gusting to 67 mph, at 10 pm EDT Sunday. St. Augustine airport had sustained winds of 38 mph with gusts as high as 51 mph Sunday night. Due to the large amount of dry air near the storm's center and west side, plus the fact the track of the storm will spend little time over water, 93L will not have time to organize into a subtropical storm that gets a name. NHC is currently giving 93L a 10% chance of becoming a named tropical or subtropical storm by Wednesday morning. This large diffuse system will bring strong winds and heavy rains to a large area of the Southeast U.S. coast over the next two days.

Elsewhere in the Atlantic, both the ECMWF and NOGAPS models predict a strong tropical disturbance could form in the Western Caribbean off the coast of Nicaragua in about seven days.


Figure 2. Radar-estimated rainfall from the Tampa Bay, Florida radar as of Monday morning.

Heavy rains for drought-stricken Texas
A slow-moving low pressure system brought the heaviest rains of the year to large portions of rain-starved Texas, Oklahoma, and Kansas over the weekend. Radar-estimated rainfall amounts reached eight inches over portions of Texas between Dallas and Abilene. Houston got 20% of their rain for the entire year--3.02"--on Sunday, breaking a string of 256 consecutive days the city had gone without a one-inch rainstorm. The longest previous such streak was 192 days, set in 1917 - 1918. The last one inch rainstorm in the city was January 24, 2011. The last time Houston had a two inch rainstorm was 383 days ago. Yesterday's rains brought the year-to-date precipitation to 15.25", which is 22" below normal.


Figure 3. Radar-estimated rainfall from the Dallas, Texas radar as of Monday morning.

Jeff Masters

Hurricane

Updated: 4:37 PM GMT on October 10, 2011

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Heavy rains for Florida; dangerous Hurricane Jova headed for Mexico

By: JeffMasters, 5:36 PM GMT on October 09, 2011

A large extratropical low pressure system with heavy rain and gale-force winds is centered over the Northwest Bahamas. Water vapor satellite loops show that the center of this low is filled with dry air, and is headed northwest at 5 - 10 mph. The low will cross over the Florida Peninsula today. The west side of this low also has a large amount of dry air, which is limiting precipitation amounts along the Gulf of Mexico coast, but the east side has plenty of tropical moisture. Radar-estimated rainfall amounts since Friday are already in excess of ten inches just inland along the Central Florida coast. Melbourne, Florida had its second wettest October day in its history yesterday, with 5.68" of rain. Much of the region, including Cocoa Beach, is under a flood watch, high surf advisories, and a high wind watch for wind gusts up to 55 mph. Winds offshore from the Florida east coast are near tropical storm strength this afternoon. Buoy 41009 offshore from Cape Canaveral recorded sustained winds of 38 mph, gusting to 47 mph, at 1 pm EDT today. Several ships have reported winds in excess of 46 mph this morning along the Florida east coast. Due to the large amount of dry air near the storm's center and west side, plus the fact the track of the storm will take it over the Florida Peninsula today and into the Florida Panhandle by Tuesday night, I doubt the storm will have time to organize into a tropical or subtropical storm that gets a name. NHC is currently giving this storm a 30% chance of becoming a named tropical or subtropical storm by Tuesday morning. This large diffuse system will bring strong winds and heavy rains to a large area of the Southeast U.S. coast over the next two days.


Figure 1. Radar-estimated rainfall from the Melbourne, Florida radar as of Sunday afternoon.

Dangerous Hurricane Jova headed for Mexico
In the Eastern Pacific off the coast of Mexico, Hurricane Jova continues to slowly intensify. Recent satellite loops show the hurricane has developed a prominent eye, and low level spiral bands have become more organized. A hurricane hunter aircraft is scheduled to arrive at Jova near 11 am PDT today. The computer models have come into excellent agreement on the track of Jova, with storm expected to hit just west of Manzanillo. The big unknown is how intense Jova will be at landfall. Jova is under light wind shear of 5 - 10 knots, and shear is predicted to stay in the low to moderate range between now and landfall. Ocean temperatures are warm, 28 - 29°C, but the warm waters do not extend to great depth, limiting Jova's potential for rapid intensification. The upper atmosphere is also not cold enough to give Jova the kind of instability typically needed for rapid intensification. Nonetheless, both the GFDL and HWRF models predict Jova will intensify into a major Category 3 and Category 4 hurricane, respectively, before landfall on Tuesday on the Mexican coast. Regardless of Jova's strength at landfall, the storm will bring very heavy rains to the Mexican coast capable of causing dangerous flash floods and mudslides, beginning on Monday.


Figure 2. Afternoon visible satellite image of Tropical Storm Irwin (left) Hurricane Jova (center) and Invest 99E (right) over the East Pacific.


Figure 3. Rainfall forecast for Hurricane Jova from this morning's 2 am EDT run of the GFDL model. Image credit: Morris Bender, NOAA/GFDL.

Tropical Storm Irwin also headed for Mexico
Once Jova has made landfall, Mexico needs to concern itself with Tropical Storm Irwin, farther to the west. The computer forecast models show Irwin could make landfall as a tropical storm on the Mexican coast late in the week, along the same stretch of coast Jova will affect. If this verifies, the one-two punch of heavy rains from two tropical cyclones within a week could cause a devastating flood situation along the Mexican coast.

Jeff Masters

Hurricane

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Heavy rains hit Florida coast; Jova and Irwin a threat to Mexico

By: JeffMasters, 1:01 PM GMT on October 08, 2011

A large low pressure system with heavy rain is developing this morning over Cuba, South Florida, and the Bahamas. The counter-clockwise flow around this low is bringing strong winds and heavy rains to much of the Florida coast. Radar-estimated rainfall amounts are already in excess of four inches along a stretch of Florida coast from West Palm Beach to Daytona Beach. Much of the region, including Cocoa Beach, is under a flood watch, high surf advisories, and a high wind watch for wind gusts of 45 - 55 mph. These these conditions will spread northwards to Georgia by Sunday, and South Carolina by Monday. I doubt that this storm will acquire enough organization to evolve into a subtropical storm that gets a name, based on the latest model output, and the fact that the storm's center may well be over the state of Florida. NHC is currently giving this storm a 20% chance of becoming a named tropical or subtropical storm by Monday morning. This is a large, diffuse system that will bring strong winds and heavy rains to a large area of the Southeast U.S. coast, regardless of the exact center location. Since the storm is going to get its start as a cold-cored upper-level low pressure system with some dry air aloft, it will not be able to intensify quickly.


Figure 1. Radar-estimated rainfall from the Melbourne, Florida radar as of Saturday morning.


Figure 2. Rainfall forecast for the 5-day period ending at 8 am EDT Thursday, October 12, 2011. The storm system affecting Florida this weekend is expected to bring up to 7 inches of rain along the coast. Heavy rains associated with a strong trough of low pressure are also expected to dump 4 - 6 inches of rain over drought-stricken areas of Texas, Oklahoma, and Kansas. Image credit: NOAA/HPC.


Heavy rain event coming for drought-stricken regions of Texas, Oklahoma, and Kansas
A strong low pressure system is expected to track across the Texas and Oklahoma Panhandles this weekend, bringing the heaviest rains of the year to drought-stricken portions of Oklahoma, Kansas, and Texas, including Abilene, where a flash flood watch is posted today. Rainfall in this region has been 13 - 20 inches below normal for the year; Lubbock, Texas has had just 3 inches of rain this year, compared to a normal of 16 inches. Rainfall amount of 1 - 4 inches will be common in the region over the weekend, and may be able to reduce drought conditions from the highest level (exceptional) to the second highest level (extreme.) However, the heaviest rains will stay confined to the western half of Texas, and Texas's major cities such as Houston will see very little rain over the weekend.


Figure 3. Visible satellite image of Hurricane Irwin and Tropical Storm Jova yesterday afternoon over the East Pacific.

Jova and Irwin: trouble for Mexico's Eastern Pacific coast
In the Eastern Pacific off the coast of Mexico, Tropical Storm Jova continues to slowly intensify. Jova will turn north and then northeast over the weekend as a strong trough of low pressure dives southward over northern Mexico. The computer models have come into better agreement on the track of Jova, with the region of coast centered on Manzanillo at greatest risk of a strike. Jova is under light wind shear of 5 - 10 knots, and shear is predicted to stay in the low to moderate range between now and landfall. Ocean temperatures are warm, 28 - 29°C, but the warm waters do not extend to great depth, limiting Jova's potential for rapid intensification. The upper atmosphere is also not cold enough to give Jova the kind of instability typically needed for rapid intensification. Nonetheless, both the GFDL and HWRF models predict Jova will intensify into a major Category 3 hurricane before landfall on Tuesday on the Mexican coast. The official NHC forecast is less aggressive, bringing Jova to Category 2 strength, which is probably reasonable, given the uncertainties regarding the possible interference from Hurricane Irwin to its west, and the fact that several other of our intensity models show very little strengthening. Regardless of Jova's strength at landfall, the storm will bring very heavy rains to the Mexican coast capable of causing dangerous flash floods and mudslides, beginning on Monday.

Once Jova has made landfall, Mexico needs to concern itself with Hurricane Irwin, farther to the west. Irwin will also be turned north and then northeast towards the coast of Mexico this weekend by the same trough of low pressure expected to affect Jova. The longer range computer forecast models show Irwin could make landfall as a hurricane on the Mexican coast late next week, along the same stretch of coast Jova will affect. If this verifies, the one-two punch of heavy rains from two tropical cyclones within a week could cause a devastating flood situation along the Mexican coast. However, the track forecast for Irwin has a higher degree of uncertainty than usual, and Baja is also at risk from this storm.

Jeff Masters

Hurricane

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Major rains for Southeast U.S., TX, KS, and OK; Jova and Irwin a threat to Mexico

By: JeffMasters, 2:24 PM GMT on October 07, 2011

A large low pressure system with heavy rain is expected to develop over Cuba, South Florida, and the Bahamas on Saturday. The counter-clockwise flow around this low will bring strong winds and heavy rains to much of the Florida coast on Saturday, and these conditions will spread northwards to Georgia by Sunday and South Carolina by Monday. I doubt that this storm will acquire enough organization to evolve into a subtropical storm that gets a name, based on the latest model output, and the fact that the storm's center may well be over the state of Florida. This will be a large, diffuse system that will bring strong winds and heavy rains to a large area of the Southeast U.S. coast, regardless of the exact center location. Portions of the coastal waters along the Florida Panhandle, as well as from Northeast Florida to South Carolina, are likely to experience sustained winds of 30 - 40 mph Monday and Tuesday. Since the storm is going to get its start as a cold-cored upper-level low pressure system with some dry air aloft, it will not be able to intensify quickly.


Figure 1. Rainfall forecast for the 5-day period ending at 8 am EDT Wednesday, October 12, 2011. The storm system affecting Florida this weekend is expected to bring up to 11 inches of rain along the coast. Heavy rains associated with a strong trough of low pressure are also expected to dump 4 - 6 inches of rain over drought-stricken areas of Texas, Oklahoma, and Kansas. Image credit: NOAA/HPC.

Heavy rain event coming for drought-stricken regions of Texas, Oklahoma, and Kansas
A strong low pressure system is expected to track across the Texas and Oklahoma Panhandles this weekend, bringing the heaviest rains of the year to drought-stricken portions of Oklahoma, Kansas, and Texas, including Abilene. Rainfall in this region has been 13 - 20 inches below normal for the year; Lubbock, Texas has had just 3 inches of rain this year, compared to a normal of 16 inches. Rainfall amount of 1 - 4 inches will be common in the region over the weekend, and may be able to reduce drought conditions from the highest level (exceptional) to the second highest level (extreme.) However, the heaviest rains will stay confined to the western half of Texas, and Texas's major cities such as Houston will see very little rain over the weekend. As of yesterday, Houston had gone 253 consecutive days without a one-inch rainstorm, a new record. The longest previous such streak was 192 days, set in 1917 - 1918. The last one inch rainstorm in the city was January 24, 2011. Remarkably, the local National Weather Service office has not issued any flood products in over a year.


Figure 2. The amount of rain needed to break the Texas drought is in excess of 15 inches (purple colors) over most of the state. This year's drought is officially Texas' worst one-year drought on record. Image credit: NOAA/NWS.

Philippe being ripped up by wind shear
Hurricane Philippe, the fifth hurricane of the 2011 Atlantic hurricane season, doesn't have much time left as a hurricane, due to high wind shear of 40 - 50 knots that is starting to tear the storm apart. Satellite loops show Philippe has become lopsided and is now missing its eye. Philippe will continue to degrade in appearance over the next few days, and will die in the middle Atlantic without affecting any land areas.


Figure 3. True-color MODIS image of Philippe over the mid-Atlantic taken at 10:45 am EDT October 6, 2011. At the time, Philippe was a Category 1 hurricane with 80 mph winds. Image credit: NASA.

Jova and Irwin: double trouble for Mexico's Eastern Pacific coast
In the Eastern Pacific off the coast of Mexico, two new tropical storms spun up yesterday. The storm of greatest immediate concern is the one closest to the coast, Tropical Storm Jova. Jova is currently headed west-northwest, parallel to the coast, but will turn north and then northeast over the weekend as a strong trough of low pressure dives southward over northern Mexico. The computer models have a fairly wide spread for the track of Jova, with the region of coast centered on Puerto Vallarta between Manzanillo and Tuxpan at greatest risk of a strike. Jova is under moderate shear of 10 - 20 knots, and shear is predicted to stay in the low to moderate range between now and landfall. Ocean temperatures are warm, 28 - 29°C, but the warm waters do not extend to great depth, limiting Jova's potential for rapid intensification. The upper atmosphere is also not cold enough to give Jova the kind of instability typically needed for rapid intensification. Nonetheless, both the GFDL and HWRF models predict Jova will intensify into a major Category 3 hurricane before landfall on Monday on the Mexican coast. The official NHC forecast is less aggressive, bringing Jova to Category 1 strength. This is probably too conservative, and I expect Jova will be at least a Cat 2 at landfall. One possible impediment to development may be Jova's close proximity to Hurricane Irwin to its west. Upper-level outflow from Irwin could weaken Jova, and the two storms may compete for the same moisture. The two storms are close enough to each other--about 650 miles apart--that they will affect each others' track, as well. Whenever two storms of at least tropical storm strength approach within 900 miles of each other, a phenomenon known as the Fujiwhara effect comes into play. This effect causes the two storms to rotate counterclockwise around a common center. Since the degree of rotation will depend on the relative strengths of the the two storms, and our ability to make good intensity forecasts is limited, the track forecasts for both Jova and Irwin will have a higher degree of uncertainty than usual. Regardless of Jova's strength at landfall, the storm will bring very heavy rains to the Mexican coast capable of causing dangerous flash floods and mudslides, beginning on Sunday night.

Once Jova has made landfall, Mexico needs to concern itself with Hurricane Irwin, which is gathering strength farther to the west. Irwin is also moving to the west-northwest, and will also be turned north and then northeast towards the coast of Mexico this weekend by the same trough of low pressure expected to affect Jova. The longer range computer forecast models show Irwin could make landfall as a hurricane on the Mexican coast late next week, along the same stretch of coast Jova will affect. If this verifies, the one-two punch of heavy rains from two tropical cyclones within a week could cause a devastating flood situation along the Mexican coast.

Jeff Masters

Drought Hurricane

Updated: 2:47 PM GMT on October 07, 2011

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Wet and windy subtropical storm possible for Southeast U.S.; Mexico eyes TD-10E

By: JeffMasters, 3:15 PM GMT on October 06, 2011

A large low pressure system with heavy rain is expected to develop over Cuba and South Florida on Saturday. The counter-clockwise flow around this low will bring strong winds and heavy rains to much of the Florida coast on Saturday, and these conditions will spread northwards to Georgia by Sunday and South Carolina by Monday. The storm may evolve into a subtropical storm that gets a name by Monday or Tuesday, but the potential location of such a storm is still murky. The extended forecast discussion from NOAA's Hydrometeorological Prediction Center favors a more westerly location, in the eastern Gulf of Mexico, as predicted by the ECMWF model. The GFS model, which puts the storm's center east of Florida, is pushing the weather system that will spawn the subtropical storm too fast to the east. In any case, the exact center location of the storm will not matter that much, since this will be a large, diffuse system that will bring strong winds and heavy rains to a large area of the Southeast U.S. coast, regardless of the exact center location. Portions of the coastal waters from Southeast Louisiana to the Florida Panhandle, as well as from Northeast Florida to South Carolina, are likely to experience sustained winds of 35 - 45 mph Monday and Tuesday. Since the storm is going to get its start as a cold-cored upper-level low pressure system with some dry air aloft, it will probably start out subtropical, with a large band of heavy rain developing well north of the center. Subtropical storms cannot intensify quickly, due to their lack of an organized inner core, and I'm not concerned at present about this storm potentially becoming a hurricane.


Figure 1. Rainfall forecast for the 5-day period ending at 8 am EDT Tuesday, October 11, 2011. The storm system affecting Florida this weekend is expected to bring up to 7 inches of rain along the coast. Heavy rains associated with a strong trough of low pressure are also expected to dump 4 - 6 inches of rain over drought-stricken areas of Texas, Oklahoma, and Kansas. Image credit: NOAA/HPC.

Philippe becomes a hurricane
After 12 days and 49 advisories, Philippe has finally intensified into hurricane, becoming the fifth hurricane of the 2011 Atlantic hurricane season. The fifth hurricane normally arrives on October 7, so this is a very average season for hurricanes, despite the fact it is already the 7th busiest season since record keeping began in 1851 for number of tropical storms--sixteen. Satellite loops show Philippe is a small hurricane with just a hint of an eye. A wide band of clouds to Philippe's northwest is associated with the trough of low pressure that has recurved Philippe to the northeast. By Friday, the trough will bring very high wind shear of 30 - 50 knots, which should cause rapid weakening. Philippe will not trouble any land areas.


Figure 2. Morning satellite image of Philippe. The band of clouds to the northwest of Philippe is associated with a cold front that has recurved Philippe to the northeast.

A double threat to Mexico's Eastern Pacific coast
In the Eastern Pacific off the coast of Mexico, two new tropical cyclones have formed. The one of greatest concern is Tropical Depression 10-E. TD 10-E is currently headed west-northwest, parallel to the coast, but will turn north and then northeast over the weekend as a strong trough of low pressure dives southward over northern Mexico. The computer models have a fairly wide spread for the track of TD-10E, with the region of coast centered on Puerto Vallarta between Manzanillo and Tuxpan at greatest risk of a strike. TD 10-E is under moderate shear of 10 - 20 knots, and shear is predicted to stay in the low to moderate range for the next five days. Ocean temperatures are warm, 28 - 29°C, but the warm waters do not extend to great depth, limiting TD-10E's potential for rapid intensification. Nonetheless, the GFDL model predicts TD-10E will intensify into a major Category 3 hurricane before landfall on Monday on the Mexican coast, and the HWRF model brings the storm to Category 2 strength. The official NHC forecast is less aggressive, bringing TD-10E to Category 1 strength, but this is conservative, and I put the odds at 30% that the storm will be a Cat 2 or stronger at landfall. One possible impediment to development may be TD-10E's close proximity to Tropical Storm Irwin to the west. Upper-level outflow from Irwin could weaken TD-10E, and the two storms may compete for the same moisture. Regardless of TD-10E's strength at landfall, the storm will bring very heavy rains to the Mexican coast capable of causing dangerous flash floods and mudslides, beginning on Monday.

Once TD-10E has made landfall, Mexico may need to concern itself with Tropical Storm Irwin, which is gathering strength farther to the west. Irwin is also moving to the west-northwest, and will also be turned north and then northeast towards the coast of Mexico this weekend by the same trough of low pressure expected to affect TD 10-E. The longer range computer forecast models show Irwin could make landfall on the Mexican coast late next week.

European heat wave: hottest October temperatures on record for the UK
The British Isles have been basking in an unprecedented October heat wave this week, which has brought the warmest temperature ever measured in the UK for the month of October. On Oct. 1, a reading of 29.9°C (85.8°F) was recorded at Gravesend, Kent, beating the previous UK October record of 29.4°C (84.9°F) at Cambridgeshire on Oct. 1, 1985. Wales also broke their warmest temperature for October with a 28.2°C (82.7°F) at Hawarden, Flintshire. Edinburgh, Scotland reached 24.7°C (76.4°F) for Scotland's warmest temperature in at least 50 years. Thanks go to wunderground's weather historian Christopher C. Burt. His latest post is on record hurricanes of the past in the Pacific Ocean.

Jeff Masters

Hurricane

Updated: 3:16 PM GMT on October 06, 2011

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Wet subtropical storm possible for Florida this weekend

By: JeffMasters, 3:29 PM GMT on October 05, 2011

A large low pressure system with heavy rains is expected to develop over Cuba and South Florida on Saturday. The counter-clockwise flow around this low will bring strong winds and heavy rains to much of the Florida coast on Saturday, and these conditions will spread northwards to Georgia by Sunday and South Carolina by Monday. Most of the models develop this system into a tropical or subtropical storm, but the potential location of such a storm is still murky. The ECMWF model predicts the storm will form in the eastern Gulf of Mexico on Monday, then move north into the Florida Panhandle on Tuesday. If this track verifies, the oil rigs off the coast of Southeast Louisiana may experience a one or two day period of sustained winds above tropical storm force Monday or Tuesday. The GFS and NOGAPS models put the storm on the other side of Florida, over the Northwestern Bahamas, and predict the storm will move northwards and hit North Carolina on Wednesday. The UKMET model is in-between, developing the storm right on top of Florida. Since the storm is going to be getting its start as a cold-cored upper-level low pressure system with some dry air aloft, it will probably start out subtropical, with a large band of heavy rain developing well north of the center, bringing heavy rains to a wide region of the Southeast U.S. Subtropical storms cannot intensify quickly, due to their lack of an organized inner core. If the storm follows the path of the GFS model, it could be similar to Subtropical Storm Four of October 4, 1974. That storm brought 10 - 14 inches of rain to the east coast of Florida and strong onshore winds of 30 - 40 mph that caused beach erosion and coastal flooding. The extended forecast discussion from NOAA's Hydrometeorological Prediction Center has a more technical discussion of this coming storm for those interested.


Figure 1. Rainfall forecast for the 5-day period ending at 8 am EDT Monday, October 10, 2011. The storm system affecting Florida this weekend is expected to bring up to 7 inches of rain along the coast. Image credit: NOAA/HPC.

Tropical Storm Philippe no threat to land
In the middle Atlantic, Tropical Storm Philippe is about to interact with a frontal system and turn northeastward out to sea. Satellite loops show Philippe is a small system with a modest amount heavy thunderstorm activity, with the surface circulation partially exposed to view by wind shear. Wind shear will remain in the moderate range today, which may allow the storm to intensify into a hurricane, as predicted by several of the intensity forecast models. By Thursday, wind shear will rise to a very high 30 - 50 knots, which should cause rapid weakening. Philippe will not trouble any land areas.


Figure 2. Morning satellite image of Tropical Storm Philippe. The band of clouds to the northwest of Philippe is associated with a cold front that is expected to absorb the storm and recurve it to the northeast on Thursday.

Jeff Masters

Hurricane

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Unprecedented Arctic ozone hole in 2011; a Florida tropical storm next week?

By: JeffMasters, 2:01 PM GMT on October 04, 2011

An unprecedented ozone hole opened in the Arctic during 2011, researchers reported this week in the journal Nature. Holes in the Antarctic ozone layer have opened up each spring since the early 1980s, but the Arctic had only shown modest springtime ozone losses in the 5% - 30% range over the past twenty years. But this year, massive ozone destruction of 80% occurred at altitudes of 18 - 20 kilometers in the Arctic during spring, resulting in Earth's first known case of twin ozone holes, one over each pole. During late March and portions of April, the Arctic ozone hole was positioned over heavily populated areas of Western Europe, allowing large levels of damaging ultraviolet rays to reach the surface. UV-B radiation causes skin damage that can lead to cancer, and has been observed to reduce crop yields in two-thirds of 300 important plant varieties studied (WMO, 2002.) The total loss of ozone in a column from the surface to the top of the atmosphere reached 40% during the peak of this year's Arctic ozone hole. Since each 1% drop in ozone levels results in about 1% more UV-B reaching Earth's surface (WMO, 2002), UV-B levels reaching the surface likely increased by 40% at the height of this year's hole. We know that an 11% increase in UV-B light can cause a 24% decrease in winter wheat yield (Zheng et al., 2003), so this year's Arctic ozone hole may have caused noticeable reductions in Europe's winter wheat crop.


Figure 1. Left: Ozone in Earth's stratosphere at an altitude of approximately 12 miles (20 kilometers) in mid-March 2011, near the peak of the 2011 Arctic ozone loss. Right: chlorine monoxide--the primary agent of chemical ozone destruction in the cold polar lower stratosphere--the same day and altitude. Image credit: NASA/JPL-Caltech.

What caused this year's unprecedented Arctic ozone hole?
Earth's ozone holes are due to the presence of human-emitted CFC gases in the stratosphere. The ozone destruction process is greatly accelerated when the atmosphere is cold enough to make clouds in the stratosphere. These polar stratospheric clouds (PSCs) act like ozone destruction factories, by providing convenient surfaces for the reactions that destroy ozone to occur. PSCs only form in the 24-hour darkness of unusually cold winters near the poles; the atmosphere is too warm elsewhere to support PSCs. Stratospheric temperatures are warmer in the Arctic than the Antarctic, so PSCs and ozone destruction in the Arctic has, in the past, been much less than in the Antarctic. In order to get temperatures cold enough to allow formation of PSCs, a strong vortex of swirling winds around the pole needs to develop. Such a "polar vortex" isolates the cold air near the pole, keeping it from mixing with warmer air from the mid-latitudes. A strong polar vortex in winter and spring is common in the Antarctic, but less common in the Arctic, since there are more land masses that tend to cause large-scale disruptions to the winds of the polar vortex, allowing warm air from the south to mix northwards. However, as the authors of the Nature study wrote, "The persistence of a strong, cold vortex from December through to the end of March was unprecedented. In February - March 2011, the barrier to transport at the Arctic vortex edge was the strongest in either hemisphere in the last ~30 years. This unusual polar vortex, combined with very cold Arctic stratospheric temperatures typical of what we've seen in recent decades, led to the most favorable conditions ever observed for formation of Arctic PSCs. The reasons for this unusual vortex are unknown.


Figure 2. Global lower stratospheric departure of temperature from average since 1979, as measured by satellites. The large spikes in 1982 and 1991 are due to the eruptions of El Chicon and Mt. Pinatubo, respectively. These volcanoes ejected huge quantities of sulphuric acid dust into the stratosphere. This dust absorbed large quantities of solar radiation, heating the stratosphere. Stratospheric temperature has been generally decreasing in recent decades, due to the twin effects of ozone depletion and the accumulation of greenhouse gases in the lower atmosphere. During Jan - Aug 2011, Earth's stratosphere had its 3rd coldest such period on record. Image credit: National Climatic Data Center.

Greenhouse gases cause stratospheric cooling
When ozone absorbs UV light, it heats the surrounding air. Thus, the loss of ozone in recent decades has helped cool the stratosphere, resulting in a feedback loop where colder temperatures create more PSCs, resulting in even more ozone destruction. However, in 1987, CFCs and other ozone-depleting substances were banned. As a result, CFC levels in the stratosphere peaked in 2000, and had fallen by 3.8% as of 2008, according to NASA. Unfortunately, despite the fact that CFCs are falling in concentration, the stratosphere is not warming up. The recovery of the ozone layer is being delayed by human emissions of greenhouse gases like carbon dioxide and methane. These gases trap heat near the surface, but cause cooling of the stratosphere and increased formation of the PSCs that help destroy ozone. We need only look as far as our sister planet, Venus, to see an example of how the greenhouse effect warms the surface but cools the upper atmosphere. Venus's atmosphere is 96.5% carbon dioxide, which has triggered a hellish run-away greenhouse effect. The average surface temperature on Venus is a sizzling 894 °F, hot enough to melt lead. Venus's upper atmosphere, though, is a startling 4 - 5 times colder than Earth's upper atmosphere. The explanation of this greenhouse gas-caused surface heating and upper air cooling is not simple, but good discussions can be found at Max Planck Institute for Chemistry and realclimate.org, for those unafraid of radiative transfer theory. One way to think about the problem is that the amount of infrared heat energy radiated out to space by a planet is roughly equal to the amount of solar energy it receives from the sun. If the surface atmosphere warms, there must be compensating cooling elsewhere in the atmosphere in order to keep the amount of heat given off by the planet the same and balanced. As emissions of greenhouse gases continue to rise, their cooling effect on the stratosphere will increase. This will make recovery of the stratospheric ozone layer much slower.

Greenhouse gases cause cooling higher up, too
Greenhouse gases have also led to the cooling of the atmosphere at levels higher than the stratosphere. Over the past 30 years, the Earth's surface temperature has increased 0.2 - 0.4 °C, while the temperature in the mesosphere, about 50 - 80 km above ground, has cooled 5 - 10 °C (Beig et al., 2006). There is no appreciable cooling due to ozone destruction at these altitudes, so nearly all of this dramatic cooling is due to the addition of greenhouse gases to the atmosphere. Even greater cooling of 17 °C per decade has been observed high in the ionosphere, at 350 km altitude. This has affected the orbits of orbiting satellites, due to decreased drag, since the upper atmosphere has shrunk and moved closer to the surface (Lastovicka et al., 2006). The density of the air has declined 2 - 3% per decade the past 30 years at 350 km altitude. So, in a sense, the sky IS falling due to the greenhouse effect!

Since any increase in solar energy would heat both the lower and upper atmosphere, the observed drop in upper atmospheric temperatures in the past 30 years argues against an increase in energy coming from the sun being responsible for global warming. The observed cooling of the upper atmosphere is strong evidence that the warming at Earth's surface is due to human-emitted greenhouse gases that trap heat near the surface and cause compensating cooling aloft. It should also give us additional confidence in the climate models, since they predicted that this upper atmospheric cooling would occur. Keep in mind, also, that 2010 was tied for Earth's hottest year on record, and the amount of energy coming from the sun during 2009 - 2010 was the lowest since satellite measurements began in the late 1970s. There has been no long-term increase in energy coming from the sun in recent decades, and the notion that global warming is due to an increase in energy coming from the sun simply doesn't add up.

Commentary
The development of an ozone hole in the Arctic is a discouraging reminder that humans are capable of causing harmful and unexpected planetary-scale changes to the environment. A 2002 assessment of the ozone layer by the World Meteorological Organization concluded that an Arctic ozone hole would be unlikely to occur, due to the lack of a strong Arctic vortex in winter, and the fact CFCs levels had started to decline. However, an Arctic ozone hole may now become a regular visitor in the future. "Day-to-day temperatures in the 2010 - 11 Arctic winter did not reach lower values than in previous cold Arctic winters," said the lead author of this year's Nature study, Gloria Manney, of NASA and the New Mexico Institute of Mining and Technology in Socorro. "The difference from previous winters is that temperatures were low enough to produce ozone-destroying forms of chlorine for a much longer time. This implies that if winter Arctic stratospheric temperatures drop just slightly in the future, for example as a result of climate change, then severe Arctic ozone loss may occur more frequently." I might add that its a very good thing CFCs were banned in 1987, or else the Arctic ozone hole would have opened up much sooner and would have been far worse. It turned out that the costs of the CFC ban, while substantial, were far less than the dire cost predictions that the CFC industry warned of. It is highly probable that we will see future nasty climate change surprises far more serious than the Arctic ozone hole if we continue on our present business-as-usual approach of emitting huge quantities of greenhouse gases. Humans would be wise to act forcefully to cut emissions of greenhouse gases, as the cost of inaction is highly likely to be far greater than the cost of action.

References
Manney, G.L., et al., 2011, Unprecedented Arctic ozone loss in 2011, Nature (2011), doi:10.1038/nature10556

Weather Underground Ozone Hole FAQ

World Meteorological Organization (WMO), "Scientific Assessment of Ozone Depletion: 2002 Global Ozone Research and Monitoring Project - Report #47", WMO, Nairobi, Kenya, 2002.

Zheng, Y., W. Gao, J.R. Slusser, R.H. Grant, C. Wang, "Yield and yield formation of field winter wheat in response to supplemental solar ultraviolet-B radiation," Agricultural and Forest Meteorology, Volume 120, Issues 1-4, 24 December 2003.


Figure 3. Morning satellite image of Tropical Storm Philippe. Philippe has a Central Dense Overcast (CDO) of high cirrus clouds characteristic of a tropical storm nearing hurricane strength.

Tropical Storm Philippe no threat to land
In the middle Atlantic, Tropical Storm Philippe has managed to grow a bit more organized in the face of high wind shear of 20 - 30 knots. Satellite loops show Philippe is a small system with a modest amount heavy thunderstorm activity, with the surface circulation partially exposed to view by wind shear. Wind shear will remain high today, but is expected to relax to the moderate range on Wednesday as Philippe recurves to the northeast. This may allow Philippe to intensify into a hurricane, as predicted by several of the intensity forecast models. It is unlikely that Philippe will trouble any land areas.

A Florida tropical storm next week?
Recent runs by all of the computer forecast models predict that an area of low pressure will develop near Florida this weekend or early next week. The counter-clockwise flow around this low will bring strong winds and heavy rains to Northeast Florida and the Georgia coast, and it is possible this storm will develop into a tropical or subtropical storm. The situation is similar to Subtropical Storm Four of October 4, 1974, according to the latest extended forecast discussion from NOAA's Hydrometeorological Prediction Center. That storm brought 10 - 14 inches of rain to the east coast of Florida and strong onshore winds of 30 - 40 mph that caused beach erosion and coastal flooding. The exact formation location of this weekend's storm is still in doubt, with the ECMWF and UKMET models predicting the storm will form in the Gulf of Mexico off the west coast of Florida, and the GFS model predicting formation over the Bahamas. We'll have to wait for future model runs before we can get a better handle on where and when this storm will most likely develop.

Jeff Masters

Ozone Layer Hurricane

Updated: 3:55 PM GMT on October 04, 2011

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Weakening Tropical Storm Ophelia hits Newfoundland

By: JeffMasters, 2:15 PM GMT on October 03, 2011

A weakening Tropical Storm Ophelia passed over Southeast Newfoundland this morning, bringing tropical storm force winds and heavy rains. Ophelia's center passed over Cape Race at about 10:30 am local time, and that station measured sustained winds of 41 mph, gusting to 61 mph. Ophelia's highest winds were recorded at Sagona Island on the south shore of Newfoundland, where sustained winds of 53 mph, gusting to 59 mph, occurred at 9:30 am local time. The capital of St. John's received 0.94" inches of rain, and recorded a peak wind gust of 40 mph this morning. Ophelia's greatest rains at any airport in Newfoundland were 1.72" at St. Pierre. Ophelia is headed out to sea at 35 mph, and will transition to an extratropical storm this afternoon.


Figure 1. Morning satellite image of Tropical Storm Ophelia.

Tropical Storm Philippe no threat to land
In the middle Atlantic, Tropical Storm Philippe continues to struggle against dry air and high wind shear. Satellite loops show Philippe is a small system with modest heavy thunderstorm activity, with the surface circulation partially exposed to view by wind shear. Wind shear is a high 30 knots, thanks to the upper-level outflow from Ophelia. Shear will remain high through Tuesday, but may relax to the moderate range as Philippe turns towards the north on Wednesday. Philippe could become a hurricane in Wednesday or Thursday when the shear relaxes. It is unlikely that Philippe will trouble any land areas.

92L over the Azores no threat to develop for several days
Elsewhere in the Atlantic, an extratropical storm with plenty of spin but no heavy thunderstorm activity is located over the Azores Islands. This storm, designated Invest 92L by NHC this morning, is over cold waters of 22 - 23°C and under very high wind shear of 40 - 50 knots. 92L is not a threat to develop today and Tuesday, and is not being given any mention in NHC's tropical weather outlook. However, 92L could start to build some heavy thunderstorms by Wednesday, as it moves west-southwest and finds warmer waters and lower wind shear. The system is unlikely to threaten any land areas.

Tropical Storm Nalgae headed for Vietnam
In the Western Pacific, Tropical Storm Nalgae will be skirting China's Hainan Island on Tuesday and Wednesday, and will make final landfall over Vietnam on Wednesday afternoon. Nalgae is not expected to regain typhoon strength. Nalgae roared ashore over the Philippines' main island of Luzon as a super typhoon with 150 mph winds at 9 am local time on Saturday morning, and is being blamed for eighteen deaths. The typhoon dumped heavy rains of 4 - 8 inches across a large swath of Northern Luzon, on soils already saturated from the rains of Typhoon Nesat just five days previously. Typhoon Nesat killed at least 52 people in the Philippines and three in China.

Jeff Masters

Hurricane

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Weakening Ophelia headed towards Newfoundland

By: JeffMasters, 3:30 PM GMT on October 02, 2011

Hurricane Ophelia is steaming north-northeastwards towards Newfoundland, Canada, as a weakening Category 2 hurricane with 110 mph winds. Yesterday, the center of Ophelia passed about 130 miles to the east of Bermuda. The Bermuda airport picked up 0.24" of rain from Ophelia's outer rain bands, and had a peak wind gust of 24 mph. Recent satellite loops show that Ophelia is asymmetric and has lost its eye, thanks to strong upper-level southwesterly winds creating 20 - 30 knots of wind shear. The shear has destroyed a portion of Ophelia's eyewall, according to recent microwave satellite imagery. With the shear expected to increase today and Ophelia about to pass over waters too cold to support a hurricane, the hurricane's eyewall should collapse tonight, resulting in rapid weakening just before the storm arrives in Newfoundland Monday morning. Ophelia will bring a 6-hour period of high winds to Southeast Newfoundland beginning around 4 am local time Monday morning. The 11 am wind probability forecast for Cape Race, Newfoundland gave it a 87% chance of receiving tropical storm force winds, a 15% chance of winds in excess of 57 mph, and no chance of hurricane force winds. The main threat to Southeast Newfoundland from Ophelia will probably be the minor to moderate flooding the storm's 2 - 4 inches of rain will cause.


Figure 1. Radar image of Ophelia as it skirted Bermuda last night, at 7:13 pm AST on October 1, 2011. At the time, Ophelia was a Category 3 hurricane with 120 mph winds. Image credit: Bermuda Weather Service.

Tropical Storm Philippe no threat to land
In the middle Atlantic, Tropical Storm Philippe continues to struggle against dry air and high wind shear. Satellite loops show Philippe is a small system with little heavy thunderstorm activity, with the surface circulation completely exposed to view by wind shear. Wind shear is a very high 30 - 40 knots, thanks to the upper-level outflow from Ophelia. This shear will remain high through Tuesday, but may relax to the moderate range as Philippe turns towards the north on Wednesday. It is unlikely that Philippe will trouble any land areas.

Elsewhere in the Atlantic, none of the computer models is calling for a new tropical storm to form in the coming seven days (though the NOGAPS model shows a strong tropical disturbance forming in the Western Caribbean in about 7 days, something it has erroneously been predicting frequently in the past few weeks.) The large-scale environment over the Atlantic currently favors sinking air, due to the current phase of the Madden-Julian Oscillation (MJO). The MJO is a 30 - 60 day cycle of thunderstorm activity that affects the tropics.


Figure 2. True-color MODIS image of Typhoon Nalgae over the Philippine Islands, taken at 03 UTC Saturday, October 1, 2011. At the time, Nalgae was a Category 3 typhoon with 120 mph winds. Image credit: NASA.

Tropical Storm Nalgae headed for Vietnam
In the Western Pacific, Tropical Storm Nalgae will be skirting China's Hainan Island on Tuesday, and will make final landfall over Vietnam on Wednesday. Nalgae is not expected to regain typhoon strength. Nalgae roared ashore over the Philippines' main island of Luzon as a super typhoon with 150 mph winds at 9 am local time on Saturday morning. The typhoon dumped heavy rains of 4 - 8 inches across a large swath of Northern Luzon, on soils already saturated from the rains of Typhoon Nesat just five days previously. Surprisingly, the death toll from Nalgae's floods is relatively low so far, with three deaths reported. Nesat killed at least 52 people in the Philippines and three in China.

Jeff Masters

Hurricane

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Ophelia brushing Bermuda; Super Typhoon Nalgae hits the Philippines

By: JeffMasters, 4:50 PM GMT on October 01, 2011

Hurricane Ophelia is steaming northwards to the east of Bermuda as a powerful Category 3 hurricane with 120 mph winds. Radar out of Bermuda shows that rain bands from Ophelia are beginning to affect the island, though as of noon Saturday, the Bermuda airport has reported just one brief rain shower and a peak wind gust of 21 mph. Recent satellite loops show that Ophelia is well-organized, with a prominent eye, good upper-level outflow, and solid lower-level spiral banding. The models agree that Ophelia will track far enough to the east of Bermuda that the island should see sustained winds below 30 mph, since it will be on the weak (left) side of the storm. The 11 am wind probability forecast from NHC gave Bermuda a 19% chance of receiving tropical storm force winds of 39 mph, and no chance of receiving hurricane force winds. Ophelia's closest approach to the island will be late Saturday night through early Sunday morning. Ophelia is likely to bring high winds and heavy rains to Southeast Newfoundland Monday. The 11 am wind probability forecast for Cape Race, Newfoundland gave it a 47% chance of receiving tropical storm force winds, and a 1% chance of hurricane force winds.


Figure 2. Morning satellite image of Ophelia.

Tropical Storm Philippe no threat to land
In the middle Atlantic, Tropical Storm Philippe continues to struggle against dry air and high wind shear. Satellite loops show Philippe is a small system with little heavy thunderstorm activity, with the surface circulation partially exposed to view by wind shear. Wind shear is a very high 30 - 40 knots, thanks to the upper-level outflow from Ophelia. This shear will remain high through Tuesday, but may relax to the moderate range as Philippe turns towards the north on Wednesday. It is unlikely that Philippe will trouble any land areas.

Elsewhere in the Atlantic, none of the computer models is calling for a new tropical storm to form in the coming seven days (though the NOGAPS model shows a strong tropical disturbance forming in the Western Caribbean in about 7 days, something it has erroneously been predicting frequently during the past few weeks.) The large-scale environment over the Atlantic currently favors sinking air, due to the current phase of the Madden-Julian Oscillation (MJO). This situation will likely last well into next week, and will discourage formation of new tropical storms. The MJO is a 30 - 60 day cycle of thunderstorm activity that affects the tropics.


Figure 2. True-color MODIS image of Typhoon Nalgae approaching the Philippine Islands, taken at 02:15 UTC Friday, September 30, 2011. At the time, Nalgae was a strengthening Category 1 typhoon with 90 mph winds. Image credit: NASA.

Super Typhoon Nalgae hits the Philippines
Typhoon Nalgae roared ashore over the Philippines' main island of Luzon as a super typhoon with 150 mph winds at 9 am local time this morning. Nalgae dumped heavy rains of 4 - 8 inches across a large swath of Northern Luzon; 4.81" of rain fell on Viganon the northwest coast of Luzon. The capital of Manila received 0.30" of rain from Nalgae, and experienced wind gusts up to 36 mph. Nalgae is the second major typhoon in a week to hit northern Luzon; on Monday, Typhoon Nesat hit the same region as a Category 3 storm with 120 mph winds, killing at least 52 people. Nalgae's rains fell on soils already saturated from Nesat's heavy rains, and the potential exists for high loss of life due to extreme flooding and mudslides. Nalgae is expected to follow a track almost exactly the same as Nesat's, passing near China's Hainan Island on Tuesday, and then hitting northern Vietnam.

Jeff Masters

Hurricane

Updated: 5:12 PM GMT on October 01, 2011

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About

Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather

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