Category 6™

Nicole kills five in Jamaica; historic rains in North Carolina; tornadoes in the Mid-Atlantic

By: JeffMasters, 2:23 PM GMT on September 30, 2010

The season's fourteenth named storm, Tropical Storm Nicole, lasted only six hours as a tropical storm, but triggered torrential heavy rains that caused havoc from the Caribbean to North Carolina. In Jamaica, flash flooding from Nicole's rains killed at least five, and several other people were swept away by flood waters and are feared dead. The storm cut power to 170,000 island residents, and caused millions of dollars in damages. Nicole dumped 6.93" of rain on Kingston, and 8.62" in the Kingston suburb of Norbrook. Rains were heavier on the western end of the island; 8.47" fell at a personal weather station at Irwindale before the power failed and data was lost.


Figure 1. NASA MODIS satellite image of Tropical Storm Nicole at 2:20pm EDT on 9/29/10. Image credit: NASA.


Figure 2. Flooding in Jamaica from Tropical Storm Nicole. Image credit: Jamaica Observer.

In Southeast Florida, Nicole brought 5.83" of rain to Miami, 9.58" to Plantation Key, and 5.44" to Homestead. However, Florida escaped serious flooding. Cuba also received widespread rain amounts of 5 - 10 inches, but there are no reports of serious flooding on the island. The remnants of Nicole will continue to bring heavy rains to portions of Cuba, the Cayman Islands, and the Bahamas today.

Historic rainfall event for eastern North Carolina
In North Carolina, the the tropical moisture streaming northwards in advance of Nicole has generated an epic rainfall event. Wilmington, NC recorded 20.69 inches of rain over the past four days, and 21.28" for the five-day period ending at 10am EDT this morning. The incredible rainfall totals have eclipsed the city's record for heaviest 4-day and 5-day rainfall events, set in September 1999 during Hurricane Floyd (19.06".) Another 1 - 3 inches of rain are likely today in Wilmington, which might make this month the rainiest month in city history. A series of non-tropical low pressure systems have been developing along a stalled front off the Carolina/North Carolina coast over the past day, and this activity will continue through tonight before the rains finally end late tonight. The historic rainfall is causing severe and damaging flooding across much of eastern North Carolina. Fortunately, eastern North Carolina was under moderate drought conditions prior to this week's rainfall onslaught, so the flooding damage will not be as great as the billions of dollars of damage wrought by Hurricane Floyd.


Figure 3. Radar-estimated precipitation for North Carolina since Sunday shows that the precursor moisture from Nicole has brought widespread rain amounts in excess of ten inches to eastern North Carolina, with over fifteen inches (white colors surrounded by dark purple) near Wilmington.

Heavy rain, flooding, and tornadoes expected from Virginia to New England
The intense plume of tropical moisture streaming northwards along the U.S. East coast will bring heavy rains of 3 - 6 inches across a wide swath of coast from North Carolina northwards to New England today and Friday. The wunderground severe weather map shows that flood warnings are already posted for portions of Pennsylvania, Maryland, and Virginia, and flood watches extend northwards though Delaware, New Jersey, New York, and the rest of New England. Tornado watches have been posted for much of the Mid-Atlantic coast, and NOAA's Storm Prediction Center has put the region in their "slight risk" area for severe weather. One tornado warning has already been issued for coastal Virginia this morning. Three possible tornadoes were reported yesterday in northeastern North Carolina.

Disturbance 97L
Two tropical waves, located 600 - 1000 miles east of the Lesser Antilles Islands, are generating a large area of disorganized thunderstorms. NHC has designated this area Invest 97L this morning. The SHIPS model predicts that wind shear over 97L will remain moderate, 10 - 20 knots, through Saturday morning, then increase to levels marginal for development, 15 - 25 knots, Saturday afternoon through Monday. Some slow development of 97L is likely over this time period, and NHC is giving it a 30% chance of developing into a tropical depression by Saturday. The system is headed west-northwest at 15 mph, and should slow down to about 10 mph by Saturday. 97L will bring heavy rains and strong gusty winds to the Lesser Antilles Islands on Sunday and Monday. The ECMWF model is the only model that develops 97L, and foresees that 97L will track across the northern Lesser Antilles and pass near Puerto Rico on Monday and the eastern Bahamas and Turks and Caicos Islands by Wednesday. There are major differences in how the models handle the steering current forecast for next week, and the long-range track of 97L is highly uncertain at this point.


Figure 4. Morning satellite image of Invest 97L. The upper right portion on the disturbance, centered near 13.5N 45W, is most likely to develop into a tropical depression.

Next update
I'll have an update Friday morning.

Jeff Masters

Flood Tornado Hurricane

Nicole's precursor moisture dumping epic rains on North Carolina

By: JeffMasters, 8:29 PM GMT on September 29, 2010

The season's fourteenth named storm, Tropical Storm Nicole, is here, but not for long. Observations from the Hurricane Hunters and satellite imagery show that the storm is being stretched along a north-south axis as it gets absorbed into a trough of low pressure along the U.S. East Coast. A separate extratropical storm is developing along a stalled-out front along the coast of South and North Carolina, and much of Nicole's moisture and energy will begin feeding into this new storm today and Thursday, leading to the demise of Nicole by Thursday. Nicole continues to dump torrential rains on Jamaica, Cuba, the Cayman Islands, South Florida, and the western Bahamas as it tracks steadily north-northeastwards up the U.S. East Coast. Some rain amounts from Nicole since yesterday morning include 9.14" at Plantation Key, FL and 8.47" at Irwindale in western Jamaica. In Southeast Florida, radar-estimated rainfall amounts of 4 - 10" are common across the coast (Figure 1.)

Surface observations don't show any winds in excess of 25 mph near the center of Nicole, and the strongest winds are located several hundred miles southeast of the center. Some of the stronger winds measured today were at Guantanamo Bay, Cuba (39 mph, gusting to 53 mph) and Cayman Brac Island in the Grand Caymans (33 mph, gusting to 43 mph).


Figure 1. Radar-estimated precipitation for South Florida. Nicole has brought over ten inches of rain to the Middle and Upper Keys.

Extreme rainfall for eastern North Carolina
In North Carolina, the the precursor moisture from Nicole has generated an epic rainfall event. Wilmington, NC has measured 15.83 inches of rain over the past three days, as of 4pm EDT. This is the city's second highest 3-day total in history, behind the 19.06" that fell in September 1999 during Hurricane Floyd. The non-tropical low pressure system developing along the South Carolina/North Carolina coast today will move northwards, giving North and South Carolina an additional blast of heavy rain tonight, which will be followed by more heavy rain from Nicole (or Nicole's remains) Thursday morning. By the time the rains from Nicole finally clear the area Thursday afternoon, an extra 5 - 10 inches will have fallen, and Wilmington will be looking at a 4-day rainfall total of 20 - 25 inches, the highest in recorded history there. Severe and damaging flooding is likely today and tomorrow from the record rains. Fortunately, eastern North Carolina was under moderate drought conditions prior to this week's rainfall onslaught, so the flooding damage will not be as great as the billions of dollars of damage wrought by Hurricane Floyd.


Figure 2. Radar-estimated precipitation for North Carolina since Saturday shows that the precursor moisture from Nicole has brought widespread rain amounts in excess of eight inches to eastern North Carolina, with over fifteen inches (white colors surrounded by dark purple) near Wilmington.

Elsewhere in the tropics
A tropical wave a few hundred miles east of the Lesser Antilles Islands is generating a modest amount of disorganized heavy thunderstorms. The wave is under a moderate 10 - 20 knots of wind shear, and has some dry air to the northwest of it that is interfering with development. None of the models develop this disturbance, and NHC is giving it a 10% chance of developing into a tropical depression by Friday. The wave is headed into a region of higher wind shear, and is not likely to develop.

Another tropical wave located about 900 miles west-southwest of the Cape Verdes Islands is more of a threat. This wave is currently moving west at 15 - 20 mph, and is generating a large area of disorganized heavy thunderstorms. Wind shear is 10 - 20 knots over the wave, and shear is forecast to decline by late this week. The latest 2am EDT runs of the NOGAPS and GFS models show some slow development of the wave late this week, and the storm is forecast to pass near the northern Lesser Antilles Islands on Sunday or Monday. NHC is giving the wave a 10% chance of developing into a tropical depression by Friday.

Disturbed weather will continue in the Western Caribbean for at least the next ten days, and the NOGAPS and GFS models continue to predict that the region could spawn a tropical depression 6 - 7 days from now. However, the models are being less aggressive about such a development than in yesterday's runs, and the models have not been consistent about the timing or location of such a storm.

Next update
I'll have an update Thursday morning.

Jeff Masters

Flood Hurricane

TD 16 dumping torrential rains; extreme rainfall event for North Carolina

By: JeffMasters, 1:54 PM GMT on September 29, 2010

Tropical Depression Sixteen is dumping torrential rains on Jamaica, Cuba, the Cayman Islands, South Florida, and the western Bahamas as it tracks steadily north-northeastwards up the U.S. East Coast. Some rain amounts from TD 16 since yesterday morning include 8.13" at Irwindale in western Jamaica, 4.75" in George Town, Cayman Islands , and 4.34" in Jucaro, Cuba. In South Florida, radar-estimated rainfall amounts of 6 - 8" are common across the Middle and Upper Keys and between West Palm Beach and Fort Pierce (Figure 1.)

Surface observations don't show any winds in excess of 25 mph near the center of TD 16, and the strongest winds associated with the storm continue to be at at Buoy 42057 400 miles to the south of Cuba, where winds were 34 mph, gusting to 43 mph, at 9:24am EDT this morning. Radar loops out of Pico San Juan, Cuba shows a region of very heavy rainfall crossing Central Cuba, and these heavy rains will move through Southeast Florida and the Western Bahamas throughout the day. Satellite imagery continues to show that TD 16's heavy thunderstorms are poorly organized, but cover a very large region of the Caribbean, western Bahamas, and eastern Florida. The thunderstorms are slowly growing more organized, and TD 16 will probably be Tropical Storm Nicole later today. An Air Force hurricane hunter aircraft is currently approaching TD 16, and will give us a better idea on its status shortly.


Figure 1. Radar-estimated precipitation for South Florida. TD 16 has brought 6 - 8 inches of rain to the Middle and Upper Keys and between West Palm Beach and Fort Pierce.

Forecast today for TD 16
Because TD 16 is so large and poorly organized, it will take it considerably more time than is usual for a tropical depression to intensify. The wind shear is moderate, 10 - 20 knots, and the waters underneath are very warm, but the storm also has to contend with passage of the center over Cuba and South Florida. All these factors considered, the strongest TD 16 is likely to get today is a 45-mph tropical storm. By tonight, wind shear will increase to the high range, 20 - 30 knots, limiting the opportunity for further intensification. Winds in South Florida should remain below 35 mph for the duration of the storm, but may reach 40 - 45 mph in the western Bahamas and in Central and Western Cuba. Since TD 16 is a large storm, heavy rain will continue to be a threat for Cuba, South Florida, and the western Bahamas through Thursday morning.

Extreme rainfall for eastern North Carolina
In North Carolina, the arrival of TD 16 is shaping up to give coastal regions one of their top five rainiest weeks in history. Tropical moisture feeding into the region ahead of TD 16 has already brought 12.88" of rain to Wilmington, NC Sunday through Tuesday, and an additional 2.37" has already fallen there so far this morning. This gives Wilmington a 4-day total of 15.25", which is the second highest 4-day total in history, behind the 19.06" that fell in September 1999 during Hurricane Floyd. A non-tropical low pressure system is predicted to develop off the Florida East Coast this afternoon and move past North Carolina late tonight, giving North and South Carolina an additional helping of heavy rain before the main rains from TD 16 arrive Thursday morning and afternoon. By the time the rains from TD 16 finally clear the area Thursday night, an additional 5 - 10 inches will have fallen, and Wilmington will probably be looking at a 4-day rainfall total of 20 - 25 inches. Severe and damaging flooding is likely. Fortunately, eastern North Carolina was under moderate drought conditions prior to this week's rainfall onslaught, so the flooding damage will not be as great as the billions of dollars of damage wrought by Hurricane Floyd.


Figure 2. Forecast precipitation for the 5-day period from 8am today through 8am EDT Monday, October 4, 2010. Image credit: NOAA Hydrometeorological Prediction Center.

Mexican landslide not as deadly as first reported
Early reports that hundreds of Mexicans may have perished in a landslide generated from the rains from the remnants of Tropical Storm Matthew turned out to be wrong. The latest news from Mexico's mountainous Oaxaca state, where the landslide occurred, is that no one has died, though eleven people are missing. Matthew hit Belize on Saturday as a minimal tropical storm with 40 mph winds, and dissipated Sunday over southern Mexico. However, Matthew's remains stalled out over the region of Mexico that had already received torrential rains from Hurricane Karl, which hit on September 18. Satellite estimates of Matthew's rains over southern Mexico show that a foot of rain may have fallen in the landslide area. Matthew's remains still linger over the region, but are probably only capable of bringing one inch of additional rain through Thursday.

Elsewhere in the tropics
A tropical wave a few hundred miles east of the Lesser Antilles Islands is generating a modest amount of disorganized heavy thunderstorms. The wave is under a moderate 10 - 20 knots of wind shear, and has some dry air to the northwest of it that is interfering with development. None of the models develop this disturbance, and NHC is giving it a 10% chance of developing into a tropical depression by Friday.

Disturbed weather will continue in the Western Caribbean for at least the next ten days, and the NOGAPS and GFS models predict that the region could spawn a tropical depression 6 - 7 days from now. However, the models are being less aggressive than earlier this week in suggesting such a development. The NOGAPS model is also suggesting that two tropical waves between the Lesser Antilles Islands and coast of Africa could develop, 6 - 8 days from now, as they pass just northeast of the Lesser Antilles Islands. The first of those waves is currently located about 400 miles southwest of the Cape Verdes Islands.

Next update
I'll have updates as the situation with TD 16 requires.

Jeff Masters

Flood Hurricane

TD 16 organizing; Mexican landslide kills hundreds; hottest day ever in Los Angeles

By: JeffMasters, 7:25 PM GMT on September 28, 2010

The large area of low pressure centered just south of Cuba's Isle of Youth has developed enough of a well-defined circulation to be classified as Tropical Depression Sixteen, and is likely to become Tropical Storm Nicole by Wednesday. The depression has a very broad center, with little heavy thunderstorm activity near the center, and is this very dissimilar to the usual types of tropical depressions we see in the Atlantic. The large size, broad center, and lack of heavy thunderstorm activity near the center of TD 16 will limit the storm's ability to rapidly intensify. TD 16 resembles the "monsoon depressions" common in India's Bay of Bengal or the Western Pacific. A monsoon depression is similar to a regular tropical depression in the winds that it generates--about 30 - 35 mph near the outer edges (and usually stronger on the eastern side of the circulation.) Monsoon depressions have large, calm centers, and can evolve into regular tropical storms, if given enough time over water to develop a tight, closed circulation. Today's monsoon-like depression in the Caribbean was able to form because the atmospheric flow pattern of the Eastern Pacific has shifted eastwards into the Western Caribbean, bringing in the Eastern Pacific ITCZ (Intertropical Convergence Zone, a region of converging surface winds that creates a band of strong thunderstorms). This unusual flow pattern is forecast to remain in place for at least the next ten days.

An Air Force hurricane hunter aircraft has been flying at 700 feet in TD 16 since 1:30pm EDT, and has thus far found a central pressure of 999 mb. The strongest winds at flight level seen as of 3:20pm EDT were 32 mph, located about 100 miles east of the center of TD 16. Surface observations show that the strongest winds at any surface station continue to be at Buoy 42057, several hundred miles to the southeast of TD 16's center. Winds were 27 mph, gusting to 34 mph at 2:43pm EDT this afternoon. Rotation of TD 16 can be seen on radar loops out of Pico San Juan, Cuba, and well as satellite imagery. The heavy thunderstorms are currently quite disorganized, but a curved band is beginning to wrap around the north side of the center, signaling that TD 16 is growing more organized. TD 16 has brought torrential rains to the Cayman Islands, Jamaica, Cuba, and Honduras today.


Figure 1. Radar-estimated precipitation for South Florida and Cuba. TD 16 has brought 2 - 4 inches of rains to the region.

Forecast for TD 16
Because TD 16 is so large, it will take more time than a typical depression for it to spin up into a strong tropical storm. Given that the steering currents are expected to pull TD 16 north-northeastwards over Cuba and into South Florida and the western Bahamas on Wednesday, the storm lacks sufficient time over water to be any stronger than a 50 mph tropical storm for Florida. TD 16 is organizing pretty slowly this afternoon, and I think the top winds in Southeast Florida are most likely to be in the 25 - 35 mph range on Wednesday. Winds are likely to be stronger in the western Bahamas, perhaps 30 - 40 mph, since they will be in the stronger right front quadrant of the storm. By the time TD 16 makes landfall in South Carolina or North Carolina on Thursday morning, it could be as strong as a 50 - 60 mph tropical storm. However, wind shear will increase sharply on Thursday as TD 16 gets caught in an upper-level trough of low pressure, and NHC is giving TD 16 only a 9% chance of making it to hurricane strength before it becomes an extratropical storm on Thursday. The primary danger from TD 16 is not wind, but heavy rainfall. A potent upper-level low and stationary front over the U.S. East Coast have been pulling moist, tropical air from the Caribbean northwards over the past few days, bringing heavy rains that have saturated the soils. This is called a Predecessor Rain Event, or PRE, since it comes in advance of the actual rain shield of the storm. (A PRE from Hurricane Karl brought southern Wisconsin the heavy rain that caused the levee on the Wisconsin River to fail yesterday.) Wilmington, NC received 10.33 inches of rain yesterday, its second greatest one-day rainfall since record keeping began in 1871. Only the 13.38" that fell during Hurricane Floyd on September 15, 1999 beat yesterday's rainfall total. With TD 16 expected to bring another 6 - 8 inches of rain to the region later this week, serious flooding is likely, and flash flood watches are posted for the North Carolina/ South Carolina border region. South Florida is also under a flood watch, for 3 - 5 inches of rain. Flooding rains of similar magnitude can also be expected in Cuba, the Cayman Islands, and the Western Bahamas through Wednesday night. Both the GFDL and HWRF models are predicting that TD 16 will dump rains in excess of eight inches along narrow portions of its path in eastern Florida, South Carolina, and North Carolina.


Figure 2. Forecast precipitation for the 5-day period from 8am today through 8am EDT Sunday, October 3, 2010. Image credit: NOAA Hydrometeorological Prediction Center.

Up to 1,000 feared dead in Mexican landslide
Mexico has taken the brunt of the devastation from the hurricane season of 2010, thanks to the landfalls of this year's two deadliest and most damaging storms, Hurricanes Alex and Karl. But Mexico's worst blow yet hit this morning, when heavy rains from the remnants of Tropical Storm Matthew triggered a landslide in Mexico's mountainous Oaxaca state that buried as many as 1,000 people in Santa Maria Tlahuitoltepec, a town of 9,000. Rescuers have not reached the area yet, but hundreds are feared dead in the 300 homes that were buried by the early morning landslide. Matthew hit Belize on Saturday as a minimal tropical storm with 40 mph winds, and dissipated Sunday over southern Mexico. However, Matthew's remains stalled out over the region of Mexico that had already received torrential rains from Hurricane Karl, which hit on September 18. Satellite estimates of Matthew's rains over southern Mexico (Figure 3) show that a foot of rain may have fallen in the landslide area. Matthew's remains still linger over the region, but are probably only capable of bringing 1 - 2 inches of additional rain through Thursday.


Figure 3. Satellite-estimated rainfall for the five-day period ending at 8pm EDT Monday September 27, 2010. The dark green colors show where rainfall amounts of 300 mm (about 12 inches) fell, due to the remnants of Tropical Storm Matthew. Image credit: Navy Research Lab, Monterey.

Elsewhere in the tropics
Once TD 16 moves out of the Caribbean, the GFS model predicts that the Western Caribbean will "reload" and produce another tropical disturbance capable of developing into a tropical depression early next week. The GFS also predicts a tropical or subtropical storm will form over the Bahamas late this week, and move north-northeast along the U.S. East Coast, missing hitting land. The NOGAPS model hints at the Bahamas storm, and also predicts development of a tropical wave a few hundred miles northeast of the Lesser Antilles Islands, about a week from now.

Hottest day in Los Angeles history
The mercury hit a blistering 113°F (45.0°C) at 12:15 pm PDT yesterday in downtown Los Angeles, making it the hottest day in Los Angeles history. It may have gotten hotter, but the thermometer broke shortly after the record high was set. The previous record in Los Angeles was 112°F set on June 26, 1990; records go back to 1877. Nearby Long Beach tied its hottest all-time temperature yesterday, with a scorching 111°F. And Christopher C. Burt, our new featured blogger on weather records, pointed out to me that a station in the foothills at 1260' elevation near Beverly Hills owned by the Los Angeles Fire Department hit 119°F yesterday--the hottest temperature ever measured in the Los Angeles area, tying the 119°F reading from Woodland Hills on July 22, 2006. Yesterday's record heat was caused by an unusually large and intense upper-level high pressure system centered over Nevada that generated winds blowing from the land to the ocean, keeping the ocean from exerting its usual cooling influence. Remarkably, Los Angeles had its second coldest summer on record this year, and temperatures just five days ago were some the coldest September temperatures in the region for the past 50 years.

The remarkable summer of 2010
Wunderground is pleased to welcome a new featured blogger--weather historian Christopher C. Burt. Chris is a leading expert in the U.S. on weather records, and is author of the world's most popular weather records book published to date, Extreme Weather: A Guide and Record Book. He's spent a lifetime collaborating with like-minded individuals from around the world, and no one--including official sources such as the National Climatic Data Center and the National Extremes Committee--has done as thorough a job correlating the various weather records available and determining the most accurate extreme values of such. Each month he'll be reporting on the notable records for heat, cold, and precipitation set world-wide, and his first post takes a look at the remarkable summer of 2010. It's great to have someone like Chris who stays on top of weather extremes, and I hope you'll pay a visit to his blog and welcome him to the wunderground site!

"Hurricane Haven" airing this afternoon
My live Internet radio show, "Hurricane Haven", will be airing again today at 4pm EDT. The call in number is 415-983-2634, or you can post a question to broadcast@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line.

Today's show will be about 30 minutes, and you can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml. The show will be recorded and stored as a podcast.

I'll have updates as the situation with TD 16 requires.

Jeff Masters

Hurricane

Caribbean disurbance 96L nearly a depression; hottest day ever in Los Angeles

By: JeffMasters, 1:54 PM GMT on September 28, 2010

Pressures continue to fall over the Western Caribbean this morning as a strong tropical disturbance (96L) organizes. Surface observations suggest that 96L has a large circulation covering most of the Western Caribbean, as evidenced by winds out of the southwest sustained at 29 - 34 mph observed at Buoy 42057 to the southeast of 96L's center this morning. Rotation of 96L can be seen on radar loops out of Pico San Juan, Cuba, and well as satellite imagery. The heavy thunderstorms are currently quite disorganized, but are bringing torrential rains to the Cayman Islands, Jamaica, Cuba, and Honduras. A Personal Weather Station in George Town on Grand Cayman Island has picked up 3.64" of rain in the twelve hours ending at 8am this morning. 96L is not the typical sort of disturbance one sees in the Atlantic, since it is much larger than normal. What has happened is that the atmospheric flow pattern of the Eastern Pacific has shifted eastwards into the Western Caribbean, bringing in the Eastern Pacific ITCZ (Intertropical Convergence Zone, a region of converging surface winds that creates a band of strong thunderstorms). 96L resembles the "monsoon depressions" common in India's Bay of Bengal or the Western Pacific. A monsoon depression is similar to a regular tropical depression in the winds that it generates--about 30 - 35 mph near the outer edges (and usually stronger on the eastern side of the circulation.) Monsoon depressions have large, calm centers, and can evolve into a regular tropical storms, if given enough time over water to develop a tight, closed circulation. The Hurricane Hunters are scheduled to fly into 96L this afternoon near 2pm EDT to see if it has become a tropical depression.


Figure 1. Morning radar image of 96L. Image credit: Cuban Institute of Meteorology.

Forecast for 96L
Because 96L is so large and lacks a well-defined surface circulation, it will take more time than a typical disturbance for it to spin up into a strong tropical storm. Given that the steering currents are expected to pull 96L north-northeastwards over Cuba and into South Florida and the western Bahamas on Wednesday, the storm lacks sufficient time over water to be any stronger than a 55 mph tropical storm for Florida. I think the top winds in Southeast Florida are likely to be in the 30 - 45 mph range on Wednesday. By the time 96L makes landfall in North Carolina or South Carolina on Thursday morning or afternoon, it could be as strong as a 55 - 65 mph tropical storm, but I think it is only 20% likely that 96L will make it to hurricane strength on Thursday. The primary danger from the storm is heavy rainfall. A potent upper-level low and stationary front over the U.S. East Coast have been bringing moist, tropical air from the Caribbean northwards over the past few days, bringing heavy rains that have saturated the soils. Wilmington, NC received 10.33 inches of rain yesterday, its second greatest one-day rainfall since record keeping began in 1871. Only the 13.38" that fell during Hurricane Floyd on September 15, 1999 beat yesterday's rainfall total. With 96L expected to bring another 6 - 8 inches of rain to the region later this week, serious flooding is likely, and flash flood watches are posted for the North Carolina/ South Carolina border region. South Florida is also under a flood watch, for 3 - 5 inches of rain. Flooding rains of similar magnitude can also be expected in Cuba, the Cayman Islands, and the Western Bahamas through Wednesday night.


Figure 2. Radar-estimated precipitation since Saturday for the North Carolina/South Carolina border region. Widespread rain amounts of 5 - 10 inches have occurred.


Figure 3. Forecast precipitation for the 5-day period from 8am today through 8am EDT Sunday, October 3, 2010. Image credit: NOAA Hydrometeorological Prediction Center.

Elsewhere in the tropics
Once 96L moves out of the Caribbean, the GFS model predicts that the Western Caribbean will "reload" and produce another tropical disturbance capable of developing into a tropical depression late this week or early next week. The other models are not showing this, but do predict a continuation of the disturbed weather pattern over the Western Caribbean. A second disturbance, if it develops, would be subject to similar steering currents, and may also move northwards across Cuba, Florida, and the Bahamas, then up the U.S. East Coast. This second disturbance might be more dangerous, since it would be dumping heavy rains on regions already drenched by 96L.

Hottest day in Los Angeles history
The mercury hit a blistering 113°F (45.0°C) at 12:15 pm PDT yesterday in downtown Los Angeles, making it the hottest day in Los Angeles history. It may have gotten hotter, but the thermometer broke shortly after the record high was set. The previous record in Los Angeles was 112°F set on June 26, 1990; records go back to 1877. Nearby Long Beach tied its hottest all-time temperature yesterday, with a scorching 111°F. And Christopher C. Burt, our new featured blogger on weather records, pointed out to me that Beverly Hills hit 119°F yesterday--the hottest temperature ever measured in the Los Angeles area, tying the 119°F reading from Woodland Hills on July 22, 2006. Yesterday's record heat was caused by an unusually large and intense upper-level high pressure system centered over Nevada that generated winds blowing from the land to the ocean, keeping the ocean from exerting its usual cooling influence. Remarkably, Los Angeles had its second coldest summer on record this year, and temperatures just five days ago were some the coldest September temperatures in the region for the past 50 years.

The remarkable summer of 2010
Wunderground is pleased to welcome a new featured blogger--weather historian Christopher C. Burt. Chris is a leading expert in the U.S. on weather records, and is author of the world's most popular weather records book published to date, Extreme Weather: A Guide and Record Book. He's spent a lifetime collaborating with like-minded individuals from around the world, and no one--including official sources such as the National Climatic Data Center and the National Extremes Committee--has done as thorough a job correlating the various weather records available and determining the most accurate extreme values of such. Each month he'll be reporting on the notable records for heat, cold, and precipitation set world-wide, and his first post takes a look at the remarkable summer of 2010. It's great to have someone like Chris who stays on top of weather extremes, and I hope you'll pay a visit to his blog and welcome him to the wunderground site!

"Hurricane Haven" airing this afternoon
My live Internet radio show, "Hurricane Haven", will be airing again today at 4pm EDT. The call in number is 415-983-2634, or you can post a question to broadcast@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line.

Today's show will be about 30 minutes, and you can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml. The show will be recorded and stored as a podcast.

I'll have updates as the situation with 96L requires.

Jeff Masters

Heat Hurricane

Huge Western Caribbean low bringing heavy rains; Wisconsin levee failing

By: JeffMasters, 12:26 PM GMT on September 27, 2010

Today, for the first day since August 20, the National Hurricane Center will not be issuing any advisories for an Atlantic named storm. Thus ends a remarkably active 36-day period that saw the formation of ten named storms, six hurricanes, and five intense hurricanes--an entire hurricane season's worth of activity, compressed into just five weeks of the six-month season. This season is not done yet, as we still have three more weeks of peak hurricane season left to go, and the Western Caribbean is looking poised to generate a tropical storm sometime in the next ten days.


Figure 1. Morning satellite image of the Western Caribbean and Central America, showing the remains of Matthew over Mexico, and a large area of disturbed weather beginning to develop over the Western Caribbean.

A wet week ahead for the Western Caribbean, Florida, and the Western Bahamas
Pressures are falling over the Western Caribbean today as a large area of low pressure develops over the region. This low is bringing heavy rains across a huge area, from the Pacific shores of El Salvador, Guatemala, and Mexico, to eastern Cuba and Haiti. All of Central America, eastern Mexico, the western 2/3 of the Caribbean, plus the Bahamas and Florida can expect sporadic periods of very heavy tropical rains over the coming week, with peak amounts of 3 - 6 inches per day possible. In the Western Caribbean, a few hundred miles east of Mexico's Yucatan Peninsula, a region of concentrated thunderstorms has built this morning, and has the potential to develop into a tropical depression by Wednesday. A large trough of low pressure over the Eastern U.S. is producing steering currents that will pull this area of disturbed weather to the north-northeast across western Cuba on Tuesday and Wednesday. The disturbance should move over Florida on Wednesday and Thursday, and over North Carolina by Thursday and Friday. All of these regions can expect very heavy rains from the disturbance, and NHC is giving a 30% chance that the disturbance will develop into a tropical depression by Wednesday. The Hurricane Hunters are on call to investigate the disturbance this afternoon, if necessary.

Once the disturbance moves out of the Caribbean, the GFS and NOGAPS models predict that the Western Caribbean will "reload" and produce another tropical disturbance capable of developing into a tropical depression late this week or early next week. The steering currents are not expected to change over the coming ten days, and Florida and western Cuba can expect to see this second disturbance potentially bring a second round of heavy rain late this week and early next week.

Levee failing in Wisconsin due to rains from Hurricane Karl's moisture
In Portage, Wisconsin, about 25 miles north of Madison, a sub-standard 120-year-old levee is failing, thanks to flood waters 3.5 feet above flood stage on the Wisconsin River. The river was swollen last week by heavy rains of up to seven inches that fell in its watershed to the northwest. The rains were generated by a plume of very moist air associated with what was Hurricane Karl. This moisture was lifted over a warm front draped over Minnesota and Wisconsin on Wednesday and Thursday. These types of rain events are called Predecessor Rain Events (PREs), because they typically precede the actual arrival of the rain shield of a tropical storm.


Figure 2. Rainfall over Minnesota and Wisconsin for the seven-day period ending 8pm EDT Sunday 9/26/10. Heavy rains to the northwest of Portage, Wisconsin led to flooding along the Wisconsin River in Portage. Image credit: NOAA.

Canadian Military responds for Hurricane Igor relief
At least twenty communities in Newfoundland, Canada are still cut off from civilization after Tuesday's rampage by Hurricane Igor. The Canadian military has sent three warships and a number of helicopters into the disaster zone to deliver food, fuel, and medical supplies to those communities still cut off. Igor killed one person and caused over $100 million in damage to the island.


Figure 3. Miniature golf anyone? A house in St. John's Newfoundland now has a very three-dimensional front yard, thanks to Hurricane Igor's winds and rain. Image credit: Zach Goudie.

I'll have an update Tuesday morning.

Jeff Masters

Flood Hurricane

Matthew dissipates; new Western Caribbean disturbance organizing

By: JeffMasters, 5:28 PM GMT on September 26, 2010

Tropical Storm Matthew has dissipated over the high mountains of Mexico, in the same region where Hurricane Karl came ashore. Matthew's remains will dump very heavy rains over a region that doesn't need it, and flash flooding and mudslide will be a concern over this region of Mexico for the next two days. Guatemala was fortunate--Matthew did dump some heavy rain of up to six inches over the country, but the storm unexpectedly moved well beyond the country, and heavy rains have avoided both Guatemala and Belize today. Venezuela was not so lucky, and heavy rains from Matthew are being blamed for the deaths of seven people in Caracas.


Figure 1. Afternoon satellite image of the Western Caribbean and Central America, showing the remains of Matthew over Mexico, and a large area of disturbed weather beginning to develop over the entire region.

Lisa
Tropical Depression Lisa is being torn apart by wind shear, and will likely not exist by Monday morning.

A wet week for the Western Caribbean
A large region of disturbed weather is developing over the Western Caribbean and Central America today. These sorts of large low pressure systems are very dangerous for Central America and the Western Caribbean, even if they do not spawn a tropical storm. In October 2007, a large low I dubbed "the sleeping giant" spent a week spinning over the region, dumping very heavy rains over all of Central America and the countries bordering the Western Caribbean. Rains from this system triggered flooding that killed 45 people in Haiti, damaged thousands of homes in Cuba, and caused heavy rains in Guatemala, El Salvador, Belize, Mexico, Jamaica, the Cayman Islands, and the Bahamas. The models predict a similar type of storm may evolve over the region over the next few days, and heavy thunderstorms from this disturbance are already affecting the Pacific coasts of Nicaragua, El Salvador, Coast Rica, and Honduras. Heavy rains will likely spread to Jamaica, Cuba, Southwest Haiti, and the Cayman Islands on Monday. These rains may be as great as 3 - 6 inches per day, and will be capable of causing dangerous flooding and mudslides. The models continue to have a poor consensus on the future evolution of this area of disturbed weather. The ECMWF model predicts that by late in the week, the low will get drawn north-northeastwards over Cuba and into South Florida and the Bahamas, and may not develop into a tropical storm. At the other extreme is the GFS model, which predicts that the low will spawn a series of two or three tropical storms over the next ten days, with each of these storms moving northwards across Cuba, South Florida, and the Bahamas. The first of these storms would organize on Monday, moving over South Florida by Wednesday, and would likely be at strongest a 50-mph tropical storm. The Hurricane Hunters are on call to investigate anything that might develop over the Western Caribbean on Monday afternoon. NHC is giving a 10% chance that something might develop in the Western Caribbean by Wednesday.

I'll have an update Monday morning.

Jeff Masters

Hurricane

Matthew drenching Central America and Mexico

By: JeffMasters, 3:35 PM GMT on September 25, 2010

Tropical Storm Matthew continues to dump heavy rains over Honduras, Belize, Guatemala, and neighboring regions of Mexico today. Puerto Barrios, in northern Guatemala, has received 4.57" of rain in the past 24 hours. With Matthew expected to slow down and dissipate by Sunday, the storm's heavy rains of 6 - 15 inches can be expected to cause severe flooding and dangerous mudslides. The rains are of particular concern for Guatemala, which suffered its rainiest August in its history, followed by the landfall of Tropical Depression 11E during the first week of September, which dumped torrential rains on the country that triggered flooding and mudslides that killed at least 48 Guatemalans.


Figure 1. Visible satellite image from NASA's Terra satellite taken yesterday, showing Tropical Storm Matthew approaching landfall.


Figure 2. Forecast rain amounts for the 5-day period beginning at 2am EDT today (Saturday, September 25) as predicted by this morning's 2am EDT (6Z) run of the GFDL. Very heavy rains in excess of eight inches (yellow colors) are predicted for portions of Central America along Matthew's track. Image credit: Morris Bender, NOAA/GFDL.

Lisa
Tropical Storm Lisa pulled a bit of a surprise last night, intensifying into a Category 1 hurricane with 80 mph winds in the far Eastern Atlantic. Lisa's longitude of 27.9W at the time made it the 10th strongest hurricane so far east in the Atlantic. Record keeping began in 1851, but it is likely that many hurricanes stronger than Lisa were missed prior to the advent of reliable satellite coverage in 1974. Lisa is even farther east than Category 4 Hurricane Julia, which earlier this month set the record for strongest hurricane ever recorded so far east. Lisa's glory will be short-lived, though, as strong upper level winds out of the west are expected to increase tonight, bringing high wind shear of 20 - 45 knots over the storm. The high shear may be capable of destroying the storm by early next week. It appears unlikely that Lisa will affect any land areas.

Forecast for the rest of the tropics
Most of the models continue to predict that by Wednesday, the remnants of Matthew, and/or a piece of a tropical disturbance over the Eastern Pacific off the coast of Guatemala, will evolve into a huge and very wet low pressure system that will start spinning over Central America and the Western Caribbean. NHC has been referring to this expected storm as a "monsoon low", and these sorts of storms are very dangerous for Central America and the Western Caribbean, even if they do not develop into a tropical storm. In October 2007, a similar monsoon low I dubbed "the sleeping giant" spent a week spinning over the region, dumping very heavy rains over all of Central America and the countries bordering the Western Caribbean. Rains from this system triggered flooding that killed 45 people in Haiti, damaged thousands of homes in Cuba, and caused havoc in Guatemala, El Salvador, Belize, Mexico, Jamaica, the Cayman Islands, and the Bahamas. A similar type of storm is likely to develop on Wednesday and Thursday, and most of Central America and the nations surrounding the Western Caribbean can expect to see dangerous flooding rains develop this week in association with this giant low. Most of the models also predict that this big low will eventually develop into a tropical storm or hurricane that would be drawn northwards over Cuba late in the week, and threaten the Bahamas, Florida, or the U.S. Gulf of Mexico coast. This is an exceptionally difficult system to forecast correctly, and the models have been coming up with some pretty unusual solutions as to what might happen. We'll just have to wait and see what unfolds over the next few days.

I'll have an update Sunday by 2pm.

Jeff Masters

Hurricane

Matthew makes landfall in Nicaragua

By: JeffMasters, 8:45 PM GMT on September 24, 2010

Satellite data shows that Tropical Storm Matthew has made landfall along the Nicaragua/Honduras coast, and is now headed inland through northern Honduras. Data from the Hurricane Hunters showed that Matthew was beginning to intensify as it made landfall, but no further intensification is likely as long as Matthew's center remains over land. We don't have many reporting stations where Matthew made landfall; Puerto Lempira, Honduras is closest, and reported sustained winds of 46 mph at 5pm CDT.


Figure 1. Forecast rain amounts for the 5-day period beginning at 8am EDT today (Friday, September 24) as predicted by this morning's 8am EDT (12Z) runs of the GFDL and HWRF models. Very heavy rains in excess of eight inches (yellow colors) are predicted by both models for portions of Central America along Matthew's track. Image credit: Morris Bender, NOAA/GFDL.

Short range forecast for Matthew
If Matthew follows the official NHC forecast and remains inland, the storm will gradually weaken and dissipate 2 - 3 days from now. If the center of Matthew emerges over water, as suggested by the HWRF model, some slight intensification could occur before Matthew makes landfall in Belize Saturday night. The SHIPS model forecasts that shear will fall to the low range, 5 - 10 knots, Saturday afternoon through Monday, so any movement of Matthew's center offshore is likely to allow intensification. The main danger for Honduras, Belize, Mexico, and northern Guatemala will be from heavy rains, not wind. The forecast rain amounts of 6 - 10 inches, with isolated amounts of 15 inches, will cause severe flooding and dangerous mudslides. Belize, northern Guatemala, northwestern Honduras, and bordering regions of Mexico's Yucatan Peninsula are most at risk from Matthew's rains, since the storm is likely to slow down and linger in these regions this weekend and early next week.

Long range forecast for Matthew
Matthew is being forced just north of due west by a strong ridge of high pressure. This ridge will keep the storm moving at 15 mph through Saturday. On Sunday, a trough of low pressure diving southwards over the Eastern U.S. will weaken the steering currents over the Western Caribbean and cause Matthew to slow to just 5 mph by Sunday night. Most of the models now show Matthew lingering over Central America long enough to dissipate. However, by Wednesday of next week, most of the models indicate that remnants of Matthew, and/or a piece of a tropical disturbance over the Eastern Pacific off the coast of Guatemala, will move into the Western Caribbean and develop into a tropical depression. The trough of low pressure over the Eastern U.S. is then likely to draw this system northwards across Cuba late next week into either Florida or the Bahamas. Whether this development would be called Matthew or Nicole is uncertain, as is the potential strength of such a storm. We'll just have to wait and see what unfolds over the next few days.

Tropical Storm Lisa
Tropical Storm Lisa continues to churn the waters of the far Eastern Atlantic. By Saturday night, upper level winds out of the west are expected to increase, bringing high wind shear of 20 - 45 knots over Lisa. The high shear may be capable of destroying the storm by early next week. It appears unlikely that Lisa will affect any land areas.

I'll have an update Saturday morning.

Jeff Masters

Hurricane

Matthew not strengthening; Igor is Newfoundland's worst hurricane in memory

By: JeffMasters, 1:53 PM GMT on September 24, 2010

Tropical Storm Matthew is bearing down on the Nicaragua/Honduras coast, but wind shear is keeping the storm from intensifying this morning. A hurricane hunter aircraft is in Matthew, and found the center pressure had risen slightly, to 1002 mb, at 8:24am EDT. Top winds seen at the surface remained at 50 mph, but winds at their flight level of 5,000 feet peaked at an unimpressive 48 mph. Satellite loops show that Matthew's heavy thunderstorm activity is mostly on the storm's south side, and this is due to strong upper level winds out of the northeast creating a moderate 10 - 20 knots of wind shear over the storm. Heavy rain squalls have moved ashore over northeastern Nicaragua and Honduras, as seen in the latest observations from Puerto Lempira, Honduras.


Figure 1. The forecast radius of tropical storm force winds of 39+ mph (dark green colors) and 58+ mph winds (lighter yellow-green colors) taken from the official 5am EDT forecast for Tropical Storm Matthew. The image was generated from our wundermap for Tropical Storm Matthew with the "hurricane" layer turned on with "wind radius" and "forecast" boxes checked.

Short range forecast for Matthew
An upper-level high pressure system lies to the northwest of Matthew, near the coast of Belize. The clockwise flow of air around this high will bring a moderate 10 - 20 knots of wind shear over Matthew today and Saturday morning. There is some dry air to the north of Matthew, and the shear may be able to drive some of this dry air into the storm, slowing intensification and keeping Matthew below hurricane strength before it makes landfall in northeastern Nicaragua late tonight. Matthew's passage over the northeast corner of Nicaragua and northeast Honduras should also act to disrupt the storm. The terrain is not mountainous in this region, though, and Matthew should be able to reorganize quickly once it emerges back into the Western Caribbean on Saturday morning. By Saturday afternoon, Matthew will move more underneath the upper-level high, resulting in much lower shear. The SHIPS model forecasts that shear will fall to the low range, 5 - 10 knots, Saturday afternoon through Monday. This drop in shear may allow for intensification of Matthew into a Category 1 hurricane before it hits Belize on Sunday morning. However, a strong tropical storm is more likely.

Impact of Matthew on Nicaragua, Honduras, and Belize
Tropical storm force winds from Matthew are forecast to extend outwards from the center between 40 - 80 nm (46 - 92 miles) as the storm moves along the north coast of Honduras this weekend. Matthew's initial forward speed of 15 mph will slow to 10 mph by Sunday morning. In combination, these factors should bring tropical storm force winds of 39+ mph to Guanaja, Roatan, and the central Honduras coast beginning between 4am - 8am EDT Saturday. These winds will last about 6 - 12 hours. Given the current weak state of Matthew, I doubt winds in excess of 50 mph will be seen on the Honduras coast as the storm passes to the north. The coast of Belize will be subject to a longer period of strong winds, since Matthew will be moving slower when it hits Belize, and may be a stronger storm. Expect 39+ mph winds to arrive at the coast of Belize between 6 - 10 pm EDT Saturday night, and persist for 12 - 16 hours, near where the center of Matthew makes landfall. A good way to compute these times of arrival and duration is to use our wundermap with the hurricane wind radius forecast layer turned on (Figure 1.) The main danger for Honduras, Belize, Mexico, and northern Guatemala will be from heavy rains, not wind. The forecast rain amounts of 6 - 10 inches, with isolated amounts of 15 inches, will cause severe flooding and dangerous mudslides. Belize is probably most at risk from Matthew's rains.

Long range forecast for Matthew
Matthew is being forced just north of due west by a strong ridge of high pressure. This ridge will keep the storm moving at 15 mph through Saturday. On Sunday, a trough of low pressure diving southwards over the Eastern U.S. will weaken the steering currents over the Western Caribbean and cause Matthew to slow to just 5 mph by Sunday night. The models are divided into two basic camps on what might happen next. One solution, championed by the ECMWF, NOGAPS, and UKMET models, has Matthew continuing inland once it makes landfall in Belize Sunday morning or afternoon. This solution means Matthew would likely dissipate over Mexico's Yucatan Peninsula. The other solution, given by the GFS, GFDL, and HWRF models, predicts Matthew will move inland over Belize for a day or so, then drift northeast and pop back out into the Western Caribbean sometime Monday or Tuesday. The key to Matthew's long range track depends upon how it interacts with a tropical low pressure area developing in the Eastern Pacific, and the trough of low pressure over the Eastern U.S. With steering currents expected to be weak, and small changes in Matthew's track making the difference between the storm being over land or water, the long range forecast for the storm is highly uncertain. It Matthew lingers in the Western Caribbean off the coast of the Yucatan Peninsula for several days, the potential exists for the storm to grow into a large and dangerous major hurricane. Sea surface temperatures and the total heat content of the Caribbean in this region are greater than the previous record highs set in 2005 (Figure 2), so there is plenty of fuel for a hurricane.

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Figure 2. Total oceanic heat content (called the Tropical Cyclone Heat Potential, or TCHP) in kilojoules per square centimeter (kJ/cm^2), for September 22 2010 (top) and the previous record high for this time of year, set in 2005 (bottom.) Category 5 Hurricane Wilma of 2005, the strongest hurricane on record in the Atlantic, reached its peak strength over the "bullseye" of high TCHP over the Western Caribbean. TCHP values are even higher this year than when Wilma formed, and TCHP in excess of 90 kJ/cm^2 (orange colors) is commonly associated with rapid intensification of hurricanes. Image credit: NOAA/AOML.

Tropical Storm Lisa
Tropical Storm Lisa continues to churn the waters of the far Eastern Atlantic. By Saturday night, upper level winds out of the west are expected to increase, bringing high wind shear of 20 - 45 knots over Lisa. The high shear may be capable of destroying the storm by early next week. It appears unlikely that Lisa will affect any land areas.

Elsewhere in the tropics
There are no other threat areas to discuss, and the GFS and NOGAPS models have backed off on their predictions of a new tropical depression forming in the Caribbean 6 - 7 days from now.

Hurricane Igor: Newfoundland's worst hurricane in memory
Newfoundland, Canada continues to reel from the effects of the punishing blow delivered by Hurricane Igor on Tuesday. The island remains devastated with many communities isolated by washed out bridges and roads. Power is impossible to restore in many areas since service crews cannot get there. The entire eastern portion of Newfoundland was cut off from the rest of the province due to a massive ravine that carved its way through the Trans-Canada Highway (Figure 3.) The road was re-opened yesterday using a temporary bridge. A summary of the impact of Igor prepared by Environment Canada puts it this way:

"Hurricane Igor and its severe impacts certainly represent a rare event in Newfoundland history which has been described as the worst in memory. In statistical terms, this was effectively a 50 - 100 year event depending on how one chooses to define it. There are no hurricanes/post tropical events of this magnitude striking Newfoundland in the modern era. Hurricane Juan in Nova Scotia was the last Atlantic Canadian hurricane to cause extreme damage. Prior to the naming of hurricanes, the 1935 Newfoundland Hurricane 75 years ago was of similar intensity."


Figure 3. A ravine carved by Hurricane Igor's flood waters washed out the Trans-Canada Highway, isolating Southeast Newfoundland from the rest of the province. Image credit: CBC News.

Igor made it all the way to southeast Newfoundland as a Category 1 hurricane, and brought sustained winds above hurricane force of 76 mph to two stations, Cape Pine and Bonavista. The storm's peak wind gust was 107 mph at Cape Pine. Igor brought sustained winds of 58 mph, gusting to 85 mph, to Newfoundland's capital, St John's. The city recorded a remarkably low pressure of 958 mb, and picked up 3.99" of rain during Igor's passage. Nearby St. Lawrence recorded its greatest 1-day rainfall event in its history, 238 mm (9.37".) Many other stations recorded 150+ mm of rain, making Igor a 1-in-100 year rainfall event. Igor's record rains were due, in part, to the storm's large size, and to the record warm sea surface temperatures over the Atlantic that allowed large amounts of water vapor to evaporate into the air surrounding Igor. Widespread rain amounts of 5 - 9 inches fell over much of southeast Newfoundland's rocky terrain, which is unable to absorb so much water. The resulting severe flooding washed out hundreds of roads, collapsed several major bridges, and forced numerous rescues of people trapped on the second stories of their homes by flood waters. Igor generated swells of 6 - 8 meters (20 - 26 feet) that pounded the southern coast of Newfoundland; significant wave heights reached 39 feet at the Newfoundland Grand Banks Buoy, and a storm surge of a meters (3.28 feet) hit the northeast shores of Newfoundland. Igor killed one person on Newfoundland, and damage may exceed $100 million, making Igor the most damaging tropical cyclone in its history.

While it is unusual for full-fledged hurricanes to affect Newfoundland, It is not that unusual for hurricanes to penetrate as far north as Newfoundland's latitude; over 40 hurricanes have done so. The last time this occurred was in 2003, when Hurricane Fabian made it to latitude 48.7°N as a hurricane. The all-time record is held by Hurricane Faith of 1966, which followed the Gulf Stream and maintained hurricane status all the way north to latitude 61.1°N, just off the coast of Norway.


Figure 4. Igor caused drastic beach erosion at Elbow Beach in Bermuda. Image credit: Extreme weather photographer Mike Theiss. He has a nice web page documenting his experience with the storm on Bermuda.

Next post
If there's a significant change to Matthew or to the forecast, I'll have an update this afternoon. Otherwise, I'll post an update Saturday by noon.

Jeff Masters

Hurricane

Tropical Depression Fifteen forms in the Caribbean

By: JeffMasters, 7:32 PM GMT on September 23, 2010

Tropical Depression Fifteen is here, and is destined to become Tropical Storm Matthew by late this afternoon or this evening. An Air Force hurricane hunter aircraft left the storm near 2pm EDT this afternoon, and on their final pass through the strong northeast quadrant of the storm, found a substantial area of surface winds of 40 - 45 mph with their SFMR instrument. Top flight level winds at 500 feet were 48 mph. These winds support upgrading TD 15 to Tropical Storm Matthew. Satellite loops show that TD 15's heavy thunderstorm activity continues to increase in intensity and areal coverage, with several respectable low-level spiral bands in evidence. There is some dry air to the northwest of TD 15, but it is currently not significantly affecting development.


Figure 1. TD 15 at 11:50am EDT 9/23/10, as seen by NASA's Terra satellite.

Forecast for TD 15
An upper-level high pressure system lies to the west of TD 15, near the coast of Nicaragua. The clockwise flow of air around this high will bring a moderate 10 - 20 knots of wind shear over TD 15 today and Friday. There is some dry continental air lying to the northwest of TD 15, and this shear may be able to drive dry air into the storm, slowing intensification and keeping TD 15 below hurricane strength through Saturday morning. By Saturday afternoon, TD 15 will move more underneath this upper-level high, causing the shear to decline. The SHIPS model forecasts that shear will fall to the low range, 5 - 10 knots, Saturday through Monday. This drop in shear should allow for intensification of TD 15 into a hurricane, if the center stays more than 50 miles offshore.

The future track and intensity of TD 15 depends critically upon the storm's interaction with land over the coming days. If TD 15 misses making landfall in Nicaragua and Honduras, and instead skirts the north coast of Honduras, the storm is likely to intensify into a hurricane by Sunday, as indicated in the official NHC forecast. However, if TD 15 spends significant time over or barely offshore of Honduras, the storm will likely stay below hurricane strength. TD 15 is being forced just north of due west by a strong ridge of high pressure. This ridge will keep the storm moving at 15 mph through Saturday. On Sunday, a trough of low pressure diving southwards over the Eastern U.S. will weaken the steering currents over the Western Caribbean and cause TD 15 to slow and turn more to the north. TD 15 will begin a period of slow and erratic movement on Sunday that may last many days, as the storm wanders in the Western Caribbean and over Belize, Honduras, and Mexico's Yucatan Peninsula. If the center of TD 15 spends significant time over water, the storm could easily develop into powerful and dangerous Hurricane Matthew. If the center remains mostly over land, TD 15 will still generate extremely heavy rains over Central America, but remain below hurricane strength. By late next week, the trough of low pressure over the Eastern U.S. may lift out, allowing a ridge of high pressure to build in and force TD 15 westwards across the Yucatan Peninsula and into the Gulf of Mexico's Bay of Campeche. Alternatively, the trough of low pressure over the Eastern U.S. may amplify, drawing TD 15 northwards across Western Cuba and into Florida. A complicating factor may be the development of a new tropical depression in the Central Caribbean 6 - 8 days from now, as predicted by both the GFS and NOGAPS models with their latest 12Z (8am EDT) runs. The uncertainties in the long-range fate of TD 15 are high, and depend strongly on slight variations in its track that determine how much time the storm spends over land. One thing that is virtually certain is that TD 15 will generate very heavy rains over Nicaragua, Honduras, Belize, and Mexico's Yucatan Peninsula Friday through Tuesday that will cause dangerous flooding rains and life-threatening mudslides.

Tropical Depression Lisa
Tropical Depression Lisa continues to churn the waters of the far Eastern Atlantic. By Saturday night, upper level winds out of the west are expected to increase, bringing high wind shear of 20 - 45 knots over Lisa. The high shear may be capable of destroying the storm by early next week. It appears unlikely that Lisa will affect any land areas.

Elsewhere in the tropics
The remnants of Hurricane Julia are still spinning over the far Eastern Atlantic, and are generating some sporadic heavy thunderstorm to the north of the center of circulation. Julia's remains are being given a 10% chance of re-developing by NHC.

Hurricane Karl's moisture causing flooding in Minnesota, Wisconsin
A plume of very moist air associated with what was Hurricane Karl last week has surged northwards over the Central U.S. over the past two days. This moisture is now being lifted over a warm front draped over Minnesota and Wisconsin, and has generated flooding rains in excess of six inches in southern Minnesota this afternoon. Flood warnings and flood watches are posted for a wide swath of the upper Midwest today, including most of southern Minnesota, northern Wisconsin, and Michigan's Upper Peninsula. These types of rain events are called Predecessor Rain Events (PREs), because they typically precede the actual arrival of the rain shield of a tropical storm.


Figure 2. Radar estimated rainfall over Minnesota.

Next post
I'll have an update on TD 15 Friday morning.

Jeff Masters

Hurricane

Dangerous Caribbean disturbance 95L close to tropical storm strength

By: JeffMasters, 1:57 PM GMT on September 23, 2010

A tropical wave (Invest 95L), moving westward at 15 mph though the south-central Caribbean, will bring gusty winds and heavy rain squalls to the northern coasts of Colombia and Venezuela this morning, as well as the Netherlands Antilles Islands. This disturbance will bring dangerous flooding rains to the countries bordering the Western Caribbean this weekend, and may also be a threat to the U.S. Gulf of Mexico coast late next week. A hurricane hunter aircraft is in 95L, and found a large region of surface winds of 35 - 45 mph to the east of 95L's center. If they find a closed circulation, 95L will be upgraded to Tropical Storm Matthew today. Satellite loops show that heavy thunderstorm activity has increased markedly in recent hours, with a solid curved band of intense thunderstorms growing to the northeast of 95L's center. Low-level spiral bands are also developing to the southeast of the center, but a closed surface circulation is not yet obvious from satellite imagery.


Figure 1. Morning satellite image of 95L.

Forecast for 95L
An upper-level high pressure system lies to the west of 95L, near the coast of Nicaragua. The clockwise flow of air around this high will bring a moderate 10 - 15 knots of wind shear over 95L today. By Friday, 95L will move more underneath this upper-level high, causing the shear to decline. The SHIPS model forecasts that shear will fall to the low range, 5 - 10 knots, by Friday afternoon. This drop in shear may allow for rapid intensification of 95L as it approaches landfall near the Nicaragua/Honduras border on Friday night and early Saturday morning. NHC is giving the disturbance an 80% chance of developing into a tropical depression by Saturday.


Figure 2. Forecast track of 95L from an ensemble of runs of the GFS model done at 2am EDT this morning.

The future of 95L depends critically upon the storm's interaction with land over the coming days. If 95L misses making landfall in Nicaragua and Honduras, and instead skirts the north coast of Honduras, the storm is likely to intensify into a hurricane by Monday, as predicted by last night's 00Z (8pm EDT) run of the GFDL model. However, if 95L spends significant time over Honduras, as predicted by the latest 06Z (2am EDT) run of the GFDL model, the storm will likely stay below hurricane strength. 95L is being forced just north of due west by a strong ridge of high pressure. This ridge will keep the storm moving at 15 mph through Saturday. On Sunday, a trough of low pressure diving southwards over the Eastern U.S. will weaken the steering currents over the Western Caribbean and cause 95L to slow and turn more to the north. 95L will begin a period of slow and erratic movement on Sunday that may last many days, as the storm wanders in the Western Caribbean and over Belize, Honduras, and Mexico's Yucatan Peninsula. If the center of 95L spends significant time over water, the storm could easily develop into powerful and dangerous Hurricane Matthew. If the center remains mostly over land, 95L will still generate extremely heavy rains over Central America, but remain below hurricane strength. By late next week, the trough of low pressure over the Eastern U.S. may lift out, allowing a ridge of high pressure to build in and force 95L westwards across the Yucatan Peninsula and into the Gulf of Mexico's Bay of Campeche. Alternatively, the trough of low pressure over the Eastern U.S. may amplify, drawing 95L northwards across Western Cuba and into Florida. The uncertainties in the long-range fate of 95L are high, and depend strongly on slight variations in its track that determine how much time the storm spends over land. One measure of the uncertainty in 95L's future track can be gained by viewing the ensemble forecast from the GFS model. An ensemble forecast is generated by taking the initial conditions in the atmosphere and making slight variations in the temperature, pressure, and humidity fields. Twenty or so tweaks of the initial conditions are made, and the GFS model run twenty separate times for each new set of initial conditions. The resulting ensemble of model runs gives one an idea of how sensitive the future track of the storm might be to errors in characterizing the initial state of the atmosphere. As one can see from this morning's GFS ensemble run (Figure 2), there are a wide range of possibilities for where 95L might go. The main thing I am confident of at this point is that 95L will generate very heavy rains over Nicaragua, Honduras, Belize, and Mexico's Yucatan Peninsula Friday through Tuesday that will likely cause dangerous flooding rains and life-threatening mudslides.

Tropical Depression Lisa
Tropical Depression Lisa continues to churn the waters of the far Eastern Atlantic. By Saturday night, upper level winds out of the west are expected to increase, bringing high wind shear of 20 - 45 knots over Lisa. The high shear may be capable of destroying the storm by early next week. It appears unlikely that Lisa will affect any land areas.

Elsewhere in the tropics
The remnants of Hurricane Julia are still spinning over the far Eastern Atlantic, and are generating some sporadic heavy thunderstorm to the north of the center of circulation. Julia's remains are being given a 10% chance of re-developing by NHC. There are no other threat areas to discuss, and none of the models is calling for development (except for 95L) over the next seven days.

Hurricane Karl's moisture causing flooding in Minnesota, Wisconsin
A plume of very moist air associated with what was Hurricane Karl last week has surged northwards over the Central U.S. over the past two days. This moisture is now being lifted over a warm front draped over Minnesota and Wisconsin, and has generated flooding rains in excess of six inches in southern Minnesota this morning. Flood warnings and flood watches are posted for a wide swath of the upper Midwest today, including most of Minnesota, northern Wisconsin, and Michigan's Upper Peninsula. The latest forecast discussion from the NWS office in Minneapolis notes that the forecast amount of moisture in the air this afternoon is similar in magnitude to the all-time record for this time of year (set on September 2, 1953.) These kinds of rain events are called Predecessor Rain Events (PREs), because they typically precede the actual arrival of the rain shield of a tropical storm.


Figure 3. Radar estimated rainfall over Minnesota.

Next post
I'll have an update on 95L later today. The timing will depend upon what the Hurricane Hunters find.

Jeff Masters

Hurricane

Igor delivers punishing blow to Newfoundland; 95L growing more organized

By: JeffMasters, 1:21 PM GMT on September 22, 2010

Hurricane Igor delivered a punishing blow to Newfoundland Canada, which suffered one of its worst poundings by a hurricane in the past century. Igor made it all the way to southeast Newfoundland yesterday as a Category 1 hurricane, bringing a peak wind gust of 107 mph to Cape Pine in Southeast Newfoundland. Igor brought sustained winds of 58 mph, gusting to 85 mph, to Newfoundland's capital, St John's. The city recorded a remarkably low pressure of 958 mb, and picked up 3.99" of rain during Igor's passage. Widespread rain amounts of 5 - 9 inches fell over much of southeast Newfoundland's rocky terrain, which is unable to absorb so much water. The resulting severe flooding washed out hundreds of roads, collapsed several major bridges, and forced numerous rescues of people trapped on the second stories of their homes by flood waters. Igor generated swells of 6 - 8 meters (20 - 26 feet) that pounded the southern coast of Newfoundland last night and this morning; significant wave heights reached 39 feet at the Newfoundland Grand Banks Buoy, and a storm surge of a meters (3.28 feet) hit the northeast shores of Newfoundland last night. Igor is now a large and powerful extratropical storm off Greenland and Labrador, and continues to generate hurricane force winds over water--winds at Angisoq, Greenland were sustained at 66 mph this morning.

It is not that unusual for hurricanes to penetrate as far north as Newfoundland's latitude; over 40 hurricanes have done so. The last time this occurred was in 2003, when Hurricane Fabian made it to latitude 48.7°N as a hurricane. The all time record is held by Hurricane Faith of 1966, which followed the Gulf Stream and maintained hurricane status all the way north to latitude 61.1°N, just off the coast of Norway.


Figure 1. Little Barsway bridge 10 km north of Grand Bank, Newfoundland, after floodwaters from Hurricane Igor swept it away. Image credit: George J.B. Rose.


Figure 2. Hurricane Igor at 11:47am EDT on Wednesday, September 21, as it pounded Newfoundland as a Category 1 hurricane with 75 mph winds. Image credit: Environment Canada.


Figure 3. Video of impressive flooding on Newfoundland's Burin Peninsula, whose 20,000 residents were cut off from the rest of the province by flooded roads and closed bridges.

Dangerous Caribbean disturbance 95L growing more organized
A tropical wave (Invest 95L) moving westward at 15 mph though the south-central Caribbean is bringing gusty winds and heavy rain to the northern coast of Venezuela and the islands of Curacao, Aruba, and Bonaire this morning. A wind gust of 38 mph was recorded at Curacao last night. Radar from Curacao and satellite loops show that 95L's thunderstorms have a pronounced rotation, with a center of circulation located just off the coast of South America. Thunderstorm activity is fairly limited, but is slowly increasing in areal coverage and intensity. Wind shear over the Caribbean is low, 5 - 10 knots, and is forecast to remain low to moderate, 5 - 15 knots, for the rest of the week. NHC is giving the disturbance a 60% chance of developing into a tropical depression by Thursday. I'd put the odds higher, at 70%. The Hurricane Hunters are scheduled to investigate 95L this afternoon.

The wave should continue moving westward near 15 mph through Friday afternoon, when it will arrive near the northern coast of Nicaragua. Most of the models show some development of 95L by Thursday or Friday, and the disturbance will bring heavy rains to the Netherlands Antilles Islands and north coast of South America on today and Thursday as passes to the north. Heavy rains may also spread to Southwest Haiti and Jamaica on Thursday, and the Cayman Islands, Cuba, Honduras, and Nicaragua on Friday. When 95L moves over or just north of Honduras on Saturday, a trough of low pressure diving southwards over the Eastern U.S. will weaken the steering currents over the Western Caribbean and cause 95L to turn more to the northwest and slow. If the center of 95L remains over water, the storm could easily develop into powerful and dangerous Hurricane Matthew over the Western Caribbean early next week. Even if the center stays over land, the circulation of the storm may be capable of generating dangerous flooding rains over Central America. Steering currents will be weak over the Western Caribbean through the middle of next week, and 95L may spend up to a week over the Western Caribbean, drenching the region with very heavy rains. Another possibility is that the trough of low pressure over the Eastern U.S. will be strong enough to draw 95L northwards across western Cuba and into the Gulf of Mexico 6 - 8 days from now. This solution is not being emphasized as much in today's model's runs as yesterday's, and the danger to the U.S. is uncertain at this point.


Figure 4. Morning satellite image of 95L.

Tropical Storm Lisa
Tropical Storm Lisa continues to churn the waters of the far Eastern Atlantic. By Friday night, upper level winds out of the west are expected to increase, bringing high wind shear of 20 - 45 knots over Lisa. The high shear may be capable of destroying the storm by early next week. It appears unlikely that Lisa will affect any land areas.

Georgette headed towards Arizona
Tropical Depression Georgette hit the tip of Baja California as a weak tropical storm with 40 mph winds yesterday, but dropped little rain. Georgette is in the Gulf of California, headed northwards, and could bring heavy rains to Arizona on Thursday.

Hurricane Karl's aftermath
Mexico continues to clean up from Hurricane Karl, which made landfall last Friday in Veracruz state as a Category 3 hurricane with 115 mph winds. Karl dumped approximately one foot of rain in the Sierra Madre Oriental Mountains, which cause some rivers to rise to unprecedented levels. The death toll from Karl's flooding and mudslides stands at 16, and ten of thousands remain in shelters after being displaced from their flooded homes. Insurance company AIR Worldwide is estimating insured losses at $100 - $200 million. Actual damage is estimated to be as much as $3.9 billion, since insurance take-up rates are low in Mexico. Karl is the second billion-dollar hurricane to hit Mexico this year; in June, Hurricane Alex hit just south of the Texas border as a Category 2 storm, killing 51 and doing $1.9 billion in damage.

Elsewhere in the tropics
The GFS model predicts a new tropical depression might develop in the Central Caribbean about seven days from now. The NOGAPS model predicts a new tropical depression will form off the coast of Africa about seven days from now.

My next post will be Thursday morning.

Jeff Masters

Hurricane

Igor pounding Newfoundland; dangerous 95L forms; 3rd hottest August for the globe

By: JeffMasters, 2:13 PM GMT on September 21, 2010

Hurricane Igor is tenaciously hanging on as a Category 1 hurricane, and is causing trouble in Newfoundland, Canada. Winds at Sagona Island, over 100 miles to the northwest of Igor's center, were sustained at 68 mph, gusting to 86, this morning, and were 56 mph, gusting to 84, at St. Pierre. Offshore, at the Newfoundland Grand Banks Buoy, winds peaked at 56 mph and significant wave heights hit 39 feet as the center of Igor passed by. Rainfall amounts of 3 - 5 inches are possible for the capital of St. Johns, where winds are already at 29 mph, gusting to 43 mph. Weather radar out of St. Johns is estimating rainfall amounts of up to 1/2 inch per hour from Igor.


Figure 1. Hurricane Igor as seen by the MODIS instrument on NASA's Terra satellite at 11:15 am EDT Monday September 20, 2010. Image credit: NASA.

Potentially dangerous Caribbean disturbance 95L forms
A tropical wave (Invest 95L) moving westward at 10 - 15 mph though the Lesser Antilles Islands is bringing gusty winds and heavy rain to the islands this morning, and has the potential to develop into a dangerous Caribbean tropical storm or hurricane late this week. The wave brought sustained winds of 30 mph to Barbados this morning, and heavy rain squalls will continue over the Lesser Antilles today. Radar from Curacao and satellite loops show that 95L's thunderstorm activity is disorganized, though increasing in areal coverage and intensity. Wind shear over the Caribbean is very low, less than 5 knots, and is forecast to remain low for the rest of the week. Water temperatures and oceanic heat content in the Caribbean are at their highest levels in recorded history, so there is plenty of fuel for development. NHC is giving the disturbance a 20% chance of developing into a tropical depression by Thursday. I'd put the odds higher, at 30%.

The wave should continue moving westward near 10 - 15 mph through Friday, when it will arrive near the northern coast of Nicaragua. Most of the models show some development of 95L by Thursday or Friday, and the disturbance will bring heavy rains to the Netherlands Antilles Islands and north coast of South America on Wednesday and Thursday as passes to the north. Heavy rains may also spread to Southwest Haiti and Jamaica on Thursday. When 95L reaches the Western Caribbean Friday, steering currents will weaken and the storm will slow, potentially bringing life-threatening heavy rains on Friday and Saturday to northern Nicaragua and northern Honduras. If the center of 95L remains over water, the storm could easily develop into a powerful and dangerous hurricane over the Western Caribbean this weekend. With a strong trough of low pressure expected to dive southwards over the Eastern U.S. and form a "cut-off" upper level low over the Southeast U.S. this weekend, this potential hurricane could get drawn northwards across western Cuba into the Gulf of Mexico. Equally likely scenarios are that 95L will stay in the Western Caribbean, or that the storm will make landfall over Nicaragua and dissipate on Friday, and never reach the Western Caribbean. It is too early to assign probabilities on which of these three scenarios is the most likely.


Figure 2. Morning satellite image of the potentially dangerous Caribbean disturbance 95L.

Tropical Storm Lisa forms
Tropical Storm Lisa, the 12th named storm of this exceptionally active 2010 Atlantic hurricane season, is now churning over the waters of the far Eastern Atlantic. Lisa is currently in an environment of low wind shear, 5 - 10 knots, which is expected to continue through Thursday. Sea Surface Temperatures are a little cool, just 27°C, and there is some dry air to the north which may slow down development. Lisa is not likely to intensify into a hurricane, which would break our string of three straight major hurricanes that have developed (Igor, Julia, and Karl.) By Thursday, upper level winds out of the west are expected to increase, bringing high wind shear of 20 - 45 knots over Lisa for the remainder of the week. It appears unlikely that Lisa will affect any land areas.

Typhoon Fanapi deluges China
Typhoon Fanapi made landfall in mainland China about 150 miles east-northeast of Hong Kong Monday morning as a Category 1 storm with 75 mph winds, dumping the heaviest rains seen in a century to the southern Guangdong Province of China, according to the provincial weather bureau. Rainfall amounts of 550 mm (21.6") were recorded in the hardest-hit Shuangyao Township in Yangchun City. Thousands of people are stranded due to washed out roads and bridges in the region. In Taiwan, where Fanapi struck as a Category 2 typhoon with 105 mph winds on Sunday, the damage total is estimated at $210 million. Fanapi killed three people on the island, and brought rains of up to 1400 mm (4.6 feet) to mountainous regions in the interior. Taipei 101, the second tallest building in the world with more than 100 stories, reportedly swayed some 15 cm in Fanapi's winds.

Georgette soaks Baja
Tropical Storm Georgette has formed in the Eastern Pacific, just off the coast of Baja California. Georgette is just the seventh named storm of a near-record quiet season, and the first storm in the Eastern Pacific since Hurricane Frank died on August 28. Georgette's main threat is heavy rain, as the storm is expected to make landfall over Baja California later today and rapidly weaken into a tropical depression by Wednesday.

Elsewhere in the tropics
The GFS model predicts a series of three tropical distubances will develop in the Caribbean over the next 1 - 2 weeks. The NOGAPS model predicts a new tropical depression will form off the coast of Africa about seven days from now.

Third warmest August on record for the globe, and 2nd warmest summer, says NOAA
August 2010 was the globe's third warmest August on record, behind 1998 and 2009, according to the National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center (NCDC). NASA's Goddard Institute for Space Studies rated August 2010 the seventh warmest August on record. Both NOAA and NASA rated the year-to-date period, January - August, as the warmest such period on record. August 2010 global ocean temperatures were the sixth warmest on record, land temperatures were the second warmest on record, Northern Hemisphere temperatures the warmest on record, and global satellite-measured temperatures for the lowest 8 km of the atmosphere the warmest on record (Remote Sensing Systems data) or 2nd warmest on record (University of Alabama Huntsville data.)

The summer of 2010 was the second warmest summer on record, behind 1998, according to the National Climatic Data Center (NCDC), and the 4th warmest summer on record according to NASA's Goddard Institute for Space Studies. It was the warmest summer on record over land areas, and fifth warmest for ocean areas, according to NOAA.

For those interested, NCDC has a page of notable weather highlights from August 2010.


Figure 3. Departure of surface temperature from average for August, 2010. Image credit: National Climatic Data Center (NCDC).

La Niña intensifies and approaches the "strong" category
The equatorial Eastern Pacific Ocean is nearing strong La Niña conditions. Sea surface temperatures (SSTs) over the tropical Eastern Pacific in the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region", dropped to 1.5 - 1.6°C below average during the first two weeks of September, according to NOAA. The Australian Bureau of Meteorology put this number at 1.3°C below average (as of September 19.) Moderate La Niña conditions are defined as occurring when this number is 1.0°C - 1.5°C below average. Temperatures colder than 1.5°C below average would qualify as strong La Niña conditions. NOAA is maintaining its La Niña advisory, and expects La Niña conditions to last through the coming spring.

Both El Niño and La Niña events have major impacts on regional and global weather patterns. For the next month, we can expect La Niña to bring cloudier and wetter than average conditions to the Caribbean, but weather patterns over North America should not see much impact. Globally, La Niña conditions tend to cause a net cooling of surface temperatures. Thus, while the past twelve month period has been the warmest globally since record keeping began in 1880, the calendar year of 2010 may end up just shy of being classified as the warmest year ever.

August 2010 Arctic sea ice extent 2nd lowest on record
Northern Hemisphere sea ice extent in August 2010 was the second lowest in the 31-year satellite record behind 2007, according to the National Snow and Ice Data Center. Strong high pressure centered north of Alaska, combined with low pressure over Siberia (the Arctic Dipole Anomaly), acted together to produce a strong flow of warm air into the Arctic, causing the near-record melting. Ice volume in August was the lowest on record for August, according to University of Washington Polar Ice Center. Arctic sea ice is currently near its annual minimum, and 2010 will end up having the second or third lowest extent on record, behind 2007 (and possibly 2008.) The fabled Northwest Passage through the normally ice-choked waters of Canada, as well as the Northeast Passage along the coast of northern Russia, remained open for ice-free navigation as of September 21, and have been ice-free for a month. This is the third consecutive year--and third time in recorded history--that both passages have melted open. Mariners have been attempting to sail these passages since 1497, and 2005 was the first year either of these passages reported ice-free conditions; 2008 was the first year both passages melted free.

"Hurricane Haven" airing this afternoon
Tune into another airing of my live Internet radio show, "Hurricane Haven", at 4pm EDT today. The call in number is 415-983-2634, or you can post a question to broadcast@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line.

Today's show will be about 30 minutes, and you can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml. The show will be recorded and stored as a podcast.

My next post will be Wednesday morning.

Jeff Masters

Hurricane

Igor spares Bermuda; Fanapi hits China; exceptionally quiet in the Pacific

By: JeffMasters, 1:29 PM GMT on September 20, 2010

The core of Category 1 Hurricane Igor passed approximately 40 miles west of Bermuda at 11 pm AST last night, bringing winds just below hurricane force to the island. Winds at the Bermuda Airport peaked at 68 mph, gusting to 93 mph, at 11:22 pm AST last night. Tropical storm force winds of 39 mph began at 10 am AST on Sunday, and were still present as of 9:38 am AST (44 mph, gusting to 53 mph.) Bermuda radar shows that the core of Igor is now well past Bermuda, with only a few spiral bands to the south that will bring occasional rain squalls to the island this morning. Pressures are rising rapidly, and the storm is almost over for Bermuda. No injuries or major damage has been reported from Bermuda thus far, though Igor's waves are being blamed for two deaths in the Caribbean, one on Puerto Rico and one on St. Croix.

Igor is headed northeastward, out to sea, but will pass close enough to southeast Newfoundland to bring tropical storm force winds there on Tuesday night. Rainfall amounts of 3 - 5 inches are possible for the capital of St. Johns.


Figure 1. The eye of Hurricane Igor as seen by the International Space Station at 9:56 am EDT September 14, 2010. At the time, Igor was a Category 4 hurricane with 135 mph winds. This image ranks as one of the top-five most spectacular hurricane images ever taken from space, in my mind. To see the full-size image, visit the NASA Earth Observatory web site.

94L
A tropical wave (Invest 94L) off the coast of Africa, a few hundred miles west of the Cape Verdes Islands, has developed a well-defined surface circulation and is threat to develop into a tropical depression. The wave is under a low 5 - 10 knots of wind shear, and is over warm 28°C waters. Dry air from the Sahara is interfering with development, and downdrafts created by mid-level dry air getting ingested into the storm are creating surface arc clouds on the west side of the storm, as seen in recent visible satellite loops. 94L only has a modest amount of heavy thunderstorm activity associated with it, and the amount of thunderstorm activity will have to increase in order for this system to be considered a tropical depression. Shear is expected to be low for the next four days, and most of the major forecast models develop 94L into a tropical depression 1 - 4 days from now. NHC is giving the wave a 80% of developing into a tropical depression by Wednesday.


Figure 2. Morning satellite image of Invest 94L.

Julia
Tropical Storm Julia is being ripped apart by wind shear from Igor, and will likely dissipate on Tuesday.

Typhoon Fanapi hits China
Typhoon Fanapi made landfall in mainland China about 150 miles east-northeast of Hong Kong this morning as a Category 1 storm with 75 mph winds. Fanapi was the strongest typhoon so far this season, peaking at Category 3 strength with 120 mph winds shortly before weakening to a Category 2 storm with 105 mph winds when it hit northern Taiwan early Sunday morning, local time. Fanapi killed three people on the island, and brought rains of up to 1400 mm (4.6 feet) to mountainous regions in the interior. Taipei 101, the second tallest building in the world with more than 100 stories, reportedly swayed some 15 cm in Fanapi's winds.

A remarkably quiet Western Pacific typhoon season and Eastern Pacific hurricane season
It has been an exceptionally quiet Western Pacific typhoon season. Before Fanapi, the strongest typhoon this season was Typhoon Kompasu, a low-end Category 3 storm with 115 mph winds that hit South Korea in early September. According to statistics forwarded to me by NOAA meteorologist Paul Stanko on Guam, by this point in an ordinary typhoon season, we should have had 17 named storms, 11 typhoons, and 2 super supertyphoons (winds of 150+ mph.) This year, we've had just 11 named storms, 5 typhoons, and no supertyphoons. The record low for a typhoon season was 18 named storms (set in 1998), 9 typhoons (set in 1998), and no supertyphoons (set in 1974.) We have a chance of beating all of these records this year. The peak date for the Western Pacific typhoon season is August 28, so we are well past the peak.

It's a similar story out in the Eastern Pacific, where a near-record quiet hurricane season is occurring. So far there have been 6 named storms, 3 hurricanes, and 2 intense hurricanes. Ordinarily, we should have had 12 named storms, 6 hurricanes, and 2 intense hurricane by this point in the season. Since reliable satellite records of Eastern Pacific hurricane activity began in 1970, the quietest season on record was 1977, when just 8 named storms occurred. The fewest hurricanes occurred in 2007 (four), and there have been two years with no intense hurricanes. The peak of Eastern Pacific hurricane season is around August 25, and on average we can expect just 3 more named storms this year. Thus, we could set records for the fewest named storms and hurricanes this year.


Figure 3. Typhoon Fanapi at landfall in China at 5:15 UTC on September 20, 2010. Image credit: NASA.

Elsewhere in the tropics
The NOGAPS, ECMWF, and GFS models have been predicting development of a strong tropical disturbance or tropical depression in the Central Caribbean 6 - 9 days from now. However, the timing, location, and track of the potential development have been inconsistent from run to run. We should merely take note of the fact that these models predict that the Caribbean will be ripe for tropical storm development late this week and early next week, and not put much faith in the specifics of these highly unreliable long-range forecasts.

I'll have a new post on Tuesday morning.

Jeff Masters

Hurricane

A weakened Igor bears down on Bermuda; 94L likely to develop

By: JeffMasters, 2:17 PM GMT on September 19, 2010

Hurricane Igor is closing in on Bermuda, but the hurricane's eyewall has collapsed, weakening Igor into a large but still dangerous Category 1 hurricane with 85 mph winds. Winds in Bermuda are rising, and exceeded tropical storm-force for the first time at 9:55 am AST this morning. Bermuda radar shows the island is now embedded in one of the main heavy rains bands of Igor, and is experiencing heavy rain and high winds. As of 11 am AST local time, winds at the Bermuda Airport were sustained at 46 mph, gusting to 63 mph. Winds will continue to rise today as the storm's core approaches. Hurricane force winds should arrive at the island between 4 - 8pm AST today, and last for 4 - 8 hours. The Bermuda Weather Service is calling for Category 1 hurricane conditions with waves of 25 - 45 feet affecting the island's offshore waters during the peak of the storm. Buildings in Bermuda are some of the best-constructed in the world, and are generally located at higher elevations out of storm surge zones; thus damage on the island may be just a few million dollars. With its eyewall gone, it is highly unlikely that Igor will be able to intensify before making landfall.


Figure 1. Hurricane Igor as seen from a "radar in space" microwave instrument on the polar-orbiting F-16 satellite at 7:36 am AST Sunday September 19, 2010. The eyewall has mostly collapsed, leaving just one fragment behind on the northwest side of Igor's center. Image credit: Navy Research Lab, Monterey.

94L
A tropical wave (Invest 94L) off the coast of Africa, a few hundred miles west of the Cape Verdes Islands, has developed a broad surface circulation and is threat to develop into a tropical depression. The wave is under a low 5 - 10 knots of wind shear, and is over warm 28°C waters. Dry air from the Sahara is interfering with development, and 94L only has a modest amount of heavy thunderstorm activity associated with it. Shear is expected to be low for the next four days, and all of the major models develop 94L into a tropical depression 1 - 3 days from now. NHC is giving the wave a 70% of developing into a tropical depression by Tuesday. With the exception of the NOGAPS model, the models predict that 94L will move northwestward out to sea.


Figure 2. Morning satellite image of Invest 94L.

Julia
Tropical Storm Julia is being ripped apart by wind shear from Igor, and will likely dissipate on Monday or Tuesday.

Typhoon Fanapi
Typhoon Fanapi made landfall in northern Taiwan early Sunday morning local time as a Category 3 storm with 120 mph winds. Fanapi killed three people on the island, and brought rains of up to 690 mm (27.2 inches) to mountainous regions in the interior. Fanapi is the strongest typhoon so far this year, in what has been an exceptionally quiet Western Pacific typhoon season. The previous strongest typhoon this season was Typhoon Kompasu, a low-end Category 3 storm with 115 mph winds that hit South Korea in early September. As seen on Taiwan radar, Fanapi has crossed over Taiwan and is now in the Taiwan Strait between the island and mainland China. Fanapi is expected to hit China about 150 miles east-northeast of Hong Kong on Monday, as a Category 1 typhoon.


Figure 3. Typhoon Fanapi at landfall in Taiwan at 7:10 local time on September 19, 2010. Image credit: Taiwan Central Weather Bureau.

Elsewhere in the tropics
In many recent runs, the NOGAPS and GFS models have been predicting development of a strong tropical disturbance or tropical depression in the Central Caribbean 6 - 9 days from now. However, the timing, location, and track of the potential development have been inconsistent from run to run. We should merely take note of the fact that these models predict that the Caribbean will be ripe for tropical storm development late this week and early next week, and not put much faith in the specifics of these highly unreliable long-range forecasts.

I'll have a new post on Monday.

Jeff Masters

Hurricane

Karl dies over Mexico's mountains; Igor bears down on Bermuda

By: JeffMasters, 4:28 PM GMT on September 18, 2010

Hurricane Karl dissipated early this morning over the high mountains east of Mexico City. Karl made landfall yesterday on the Mexican coast about ten miles northwest of Veracruz at 1pm EDT, as a Category 3 hurricane with 115 mph winds. Karl was the first landfalling major hurricane in the Atlantic basin since Hurricane Ike over Cuba in 2008, and the first major hurricane to make landfall on the Gulf of Mexico coast since Hurricane Wilma in Southwest Florida in 2005. Veracruz was on the weak (left) side of Karl's eyewall, and did not receive hurricane force winds, except perhaps at the extreme northern edge of the city. Winds at the Veracruz Airport, located on the west side of the city, peaked at sustained speeds of 46 mph, gusting to 58 mph, at 11:54am local time. Karl has dumped very heavy rains in Mexico's Veracruz state, with 218 mm (8.6") measured at Hacienda Yland Ylang, and 171 mm (6.7") at Japala.


Figure 1. Hurricane Karl as seen in this visible moonlight image from the F-16 polar orbiting satellite at 9:08pm EDT Thursday, September 16, 2010. The bright city lights of Mexico City are visible due west of Karl, and gas flares from the PEMEX drilling platforms in the Gulf of Mexico to the east of Karl also make a bright splash of light. Image credit: Navy Research Lab, Monterey.

Igor
The Hurricane Hunters just arrived in Hurricane Igor, and found that the inner 23-mile wide eyewall had collapsed. Igor now has a huge 92-mile wide eye, thanks to this eyewall replacement cycle. As is usually the case in eyewall replacement cycles, the peak winds of the hurricane have decreased, but hurricane force winds are now spread out over a larger area. Top winds at the surface as seen by the SFMR instrument were Category 1 strength, 82 mph, though the aircraft did see 130 mph winds at 10,000 feet, which suggests the surface winds should be of Category 3 strength, 115 mph. These stronger winds are apparently not mixing down to the surface in the usual fashion. A sonde dropped in the eye at 11:20am AST recorded a central pressure of 945 mb, about 6 mb higher than what NHC was estimating in their 11am AST advisory. Though conditions for intensification will remain favorable through Sunday afternoon, with moderate wind shear of 10 - 20 knots and warm water temperatures of 28.5°C, we can expect only slow intensification of Igor. With such a huge eye, it will take Igor considerable time for it to bring the winds in this new eyewall back to Category 3 strength, and it will be difficult for the hurricane to be stronger than a high-end Category 2 storm with 110 mph winds when it makes its closest pass by Bermuda Sunday night.


Figure 2. Hurricane Igor as seen from a "radar in space" microwave instrument on the polar-orbiting F-16 satellite at 7:50 am AST Saturday September 18, 2010. A 22-mile wide inner eyewall was collapsing, and being replaced by a huge 92-mile diameter outer eyewall. Image credit: Navy Research Lab, Monterey.

Igor's impact on Bermuda
Hurricane warnings are flying for Bermuda, and winds are starting to rise on the island. Winds were blowing out of the northeast and had risen to 22 mph as of noon local time today. Igor's outer rain bands are now visible on Bermuda radar, and will reach the island late this afternoon. Igor is a huge storm, and tropical storm force winds extend out 340 miles to the north of its center. Igor will be moving at about 12 - 13 mph during its approach to Bermuda, so the island can expect a period of 39+ mph tropical storm force winds to begin near 7 - 9pm AST tonight. Hurricane force winds will arrive at the island near 8 - 10pm AST Sunday night, and last for 8 - 10 hours. Igor will speed up to about 15 mph as it passes the island near midnight Sunday night, and Bermuda's battering by tropical storm force winds will not be as long as Igor moves away, perhaps 12 - 14 hours. The Bermuda Weather Service is calling for Category 2 hurricane conditions to arrive at the island on Sunday night, with waves of 20 - 45 feet affecting the island's offshore waters during the peak of the storm. Buildings in Bermuda are some of the best-constructed in the world, and are generally located at higher elevations out of storm surge zones. If Igor remains below Category 3 strength, as currently appears likely, damage on the island may be just a few million dollars. According to AIR Worldwide, "Homes in Bermuda are typically one or two stories and constructed of 'Bermuda Stone,' a locally quarried limestone, or of concrete blocks. Roofs are commonly made of limestone slate tiles cemented together. Commercial buildings, typically of reinforced concrete construction, rarely exceed six stories. In both residential and commercial buildings, window openings are generally small and window shutters are common. These features make Bermuda's building stock quite resistant to winds, and homes are designed to withstand sustained winds of 110 mph and gusts of up to 150 mph."

Bermuda's hurricane history
Igor is similar in strength and projected track to Hurricane Fabian of 2003. Fabian hit Bermuda as a Category 3 hurricane with 120 mph winds. It was the most damaging hurricane ever to hit the island, with $355 million in damage. Fabian's storm surge killed four people crossing a causeway on the island. These were the first hurricane deaths on Bermuda since 1926. The most powerful hurricane on record to strike Bermuda was the Category 4 Havana-Bermuda Hurricane, which hit on October 22, 1926, with 135 mph winds. The hurricane sank two British warships, claiming 88 lives, but no one was killed on the island. The deadliest hurricane to affect the island occurred on September 12, 1839, when a Category 3 hurricane with 125 mph winds and an 11-foot storm surge hit, tearing off the roofs of hundreds of buildings and wrecking several ships. An estimated 100 people were killed (source: Encyclopedia of Hurricanes, Typhoons, and Cyclones, by David Longshore.)

94L
A tropical wave (Invest 94L) off the coast of Africa, a few hundred miles southwest of the Cape Verdes Islands, has developed a broad surface circulation and is threat to develop into a tropical depression early next week. The wave is under a moderate 10 - 20 knots of wind shear, and is over warm 28°C waters. Dry air from the Sahara is interfering with development, and 94L only has a small amount of heavy thunderstorm activity associated with it. Shear is expected to be low to moderate for the next four days, and 94L should be able to develop into a tropical depression if it can fight off the dry air to its north. The ECMWF model develops 94L into a tropical depression 4 - 5 days from now. NHC is giving the wave a 30% of developing into a tropical depression by Monday. Steering currents favor 94L moving northwest out to sea.

Typhoon Fanapi
The strongest typhoon of the very quiet Western Pacific typhoon season is now Typhoon Fanapi, a Category 3 storm with 120 mph winds. Fanapi is on track to hit Taiwan on Sunday morning as a Category 3 typhoon, then hit mainland China on Monday morning as a tropical storm. The previous strongest typhoon this season was Typhoon Kompasu, a low-end Category 3 storm with 115 mph winds that hit South Korea in early September.


Figure 3. Typhoon Fanapi at 04:45 UTC on September 17, 2010, as it approached Taiwan from the Philippine Sea. Image credit: NASA.

Elsewhere in the tropics
An area of disturbed weather off the coast of South Texas is due to an region of upper level winds that are spreading out, encouraging thunderstorm updrafts to pull more air aloft. I don't expect this region to develop due to its close proximity to the coast. The NOGAPS model is predicting development of a strong tropical disturbance in the Western Caribbean 6 - 7 days from now. The GFS model has backed off developing anything in the Caribbean next week.

I'll have a new post on Sunday.

Jeff Masters

Hurricane

Karl makes landfall near Veracruz; Igor slightly weaker

By: JeffMasters, 8:29 PM GMT on September 17, 2010

Hurricane Karl made landfall on the Mexican coast ten miles north of Veracruz at 1pm EDT today as a Category 3 hurricane with 115 mph winds. Veracruz was on the weak (left) side of Karl's eyewall, and did not receive hurricane force winds, except perhaps at the extreme northern edge of the city. Winds at the Veracruz Airport, located on the west side of the city, peaked at sustained speeds of 46 mph, gusting to 58 mph, at 11:54am local time. Radar out of Alvarado shows that Karl has kept its eyewall intact well inland, even as the storm moves into the high mountains east of Mexico City. Karl was the first major hurricane on record in the Bay of Campeche--the region of the Gulf of Mexico bounded by the Yucatan Peninsula on the east. There were two other major hurricanes that grazed the northern edge of the Bay of Campeche, Hurricane Hilda of 1955 and Hurricane Charley of 1951, but Karl is by far the farthest south a major hurricane has been in the Gulf of Mexico. Hurricane records go back to 1851, but Karl is a small storm and could have gotten missed as being a major hurricane before the age of aircraft reconnaissance (1945).


Figure 1. Tracks of all major hurricanes since 1851 near Mexico's Bay of Campeche. Karl is most southerly storm on record in the Gulf of Mexico. Image credit: NOAA Coastal Services Center.

With Karl's ascension to major hurricane status, we are now ahead of the pace of the terrible hurricane seasons of 2004 and 2005 for number of major hurricanes so early in the year. In 2005, the fifth major hurricane (Rita) did not occur until September 21, and in 2004, the fifth major hurricane (Karl) arrived on September 19. Wunderblogger Cotillion has put together a nice page showing all the seasons with five or more major hurricanes. The last time we had five major hurricanes earlier in the season was in 1961, when the fifth major hurricane (Esther) arrived on September 13. This morning we continue to have three simultaneous hurricanes, Hurricanes Igor, Julia, and Karl. This is a rare phenomena, having occurred only eight previous years since 1851. The last time we had three simultaneous hurricanes in the Atlantic was in 1998. That year also had four simultaneous hurricanes--Georges, Ivan, Jeanne and Karl--for a brief time on September 25. There has been just one other case of four simultaneous Atlantic hurricanes, on August 22, 1893. The year 2005 came within six hours of having three hurricanes at the same time, but the official data base constructed after the season was over indicates that the three hurricanes did not exist simultaneously.

Also remarkable this year is that are seeing major hurricanes in rare or unprecedented locations. Julia was the strongest hurricane on record so far east, Karl was the strongest hurricane so far south in the Gulf of Mexico, and Earl was the 4th strongest Atlantic hurricane so far north. This unusual major hurricane activity is likely due, in part, to the record Atlantic sea surface temperatures this year.


Figure 2. Hurricane Karl as seen by the MODIS instrument on NASA's Terra satellite at 12:20 pm CDT on Thursday, September 16, 2010. Image credit: NASA.


Figure 3. Radar image of Karl at landfall in Mexico. Image credit: Mexican Weather Service.

Impact of Karl on Mexico
Given that the Bay of Campeche coast has never experienced a hurricane as strong as Karl, its impact is likely to cause major damage to a 50-mile wide coastal area beginning ten miles north of Veracruz. Fortunately, the coast is not heavily populated there, and is not particularly low-lying, so the 12 - 15 foot storm surge will not be the major concern from Karl. The main concern will be flooding from Karl's torrential rains. The region has been hit by three Category 2 hurricanes over the past 55 years, and two of these storms caused flooding that killed hundreds. The strongest hurricanes in history to affect the region were Item in 1950, with 110 mph winds, Janet in 1955, with 100 mph winds, and Diana of 1990, with 100 mph winds. Flooding from Janet killed over 800 people in Mexico. and flooding from Diana killed at least 139 people. Karl's high winds are also a major concern, and these winds are likely to extensive damage.

Igor
The Hurricane Hunters just left Hurricane Igor, and found that the hurricane has continued to slowly weaken. On their last pass through the eye of Igor at 1:49 pm EDT, an Air Force hurricane hunter aircraft found a central pressure of 947 mb. The eyewall was missing a chunk on its southwest side. Top winds at the surface as seen by their SFMR instrument were barely Category 1 strength, 76 mph, though the aircraft did see 117 mph winds at 10,000 feet, which suggests the surface winds were probably of Category 2 strength, 105 mph.


Figure 4. Hurricane Igor as seen by the MODIS instrument on NASA's Terra satellite at 10:50 am EDT on Thursday, September 16, 2010. Image credit: NASA.

Igor's impact on Bermuda
Hurricane warnings are now flying for Bermuda, and tropical storm force winds will arrive at the island late Saturday night. Igor is a huge storm, and tropical storm force winds extend out 290 miles to the north of its center. As the hurricane moves north, it will expand in size, as it takes advantage of the extra spin available at higher latitudes due to Earth's rotation. By Saturday night, Igor's tropical storm force winds are expected to extend outwards 320 miles from the center. Igor will be moving at about 11 - 13 mph during the final 24 hours of its approach to Bermuda, so the island can expect a period of 39+ mph tropical storm force winds to begin near midnight Saturday night--a full 24 hours before the core of Igor arrives. Igor will speed up to about 15 mph as it passes the island near midnight Sunday night, and Bermuda's battering by tropical storm force winds will not be as long as Igor moves away, perhaps 10 hours long. Hurricane force winds will probably extend out about 70 miles from the center when the core of Igor reaches Bermuda, and the island can expect to be pounded by hurricane force winds for up to 6 - 8 hours. In all, Bermuda is likely to suffer a remarkably long 36-hour period of tropical storm force winds, with the potential for many hours of hurricane force winds. Long duration poundings like this are very stressful for buildings, and there is the potential for significant damage on Bermuda. However, buildings in Bermuda are some of the best-constructed in the world, and if Igor weakens to Category 2 strength, as appears likely, damage on the island may be just a few million dollars. According to AIR Worldwide, "Homes in Bermuda are typically one or two stories and constructed of 'Bermuda Stone,' a locally quarried limestone, or of concrete blocks. Roofs are commonly made of limestone slate tiles cemented together. Commercial buildings, typically of reinforced concrete construction, rarely exceed six stories. In both residential and commercial buildings, window openings are generally small and window shutters are common. These features make Bermuda's building stock quite resistant to winds, and homes are designed to withstand sustained winds of 110 mph and gusts of up to 150 mph."

Bermuda's hurricane history
Igor is similar in strength and projected track to Hurricane Fabian of 2003. Fabian hit Bermuda as a Category 3 hurricane with 120 mph winds. It was the most damaging hurricane ever to hit the island, with $355 million in damage. Fabian's storm surge killed four people crossing a causeway on the island. These were the first hurricane deaths on Bermuda since 1926. The most powerful hurricane on record to strike Bermuda was the Category 4 Havana-Bermuda Hurricane, which hit on October 22, 1926, with 135 mph winds. The hurricane sank two British warships, claiming 88 lives, but no one was killed on the island. The deadliest hurricane to affect the island occurred on September 12, 1839, when a Category 3 hurricane with 125 mph winds and an 11-foot storm surge hit, tearing off the roofs of hundreds of buildings and wrecking several ships. An estimated 100 people were killed (source: Encyclopedia of Hurricanes, Typhoons, and Cyclones, by David Longshore.)

Elsewhere in the tropics
A tropical wave off the coast of Africa, a few hundred miles south of the Cape Verdes Islands, is disorganized, but has the potential for some slow development over the next few days. The NOGAPS model develops this wave into a tropical depression 4 - 5 days from now. NHC is giving the wave a 10% of developing into a tropical depression by Sunday.

I'll have a new post on Saturday.

Jeff Masters

Hurricane

Hurricane Karl: first major hurricane ever in the Bay of Campeche; Bermuda eyes Igor

By: JeffMasters, 2:47 PM GMT on September 17, 2010

Hurricane Karl explosively deepened into a dangerous Category 3 hurricane this morning, becoming the fifth major hurricane of this remarkably active 2010 Atlantic hurricane season. Karl is the first major hurricane on record in the Gulf of Mexico's Bay of Campeche--the region bounded by the Yucatan Peninsula on the east. There were two other major hurricanes that grazed the northern edge of the Bay of Campeche, Hurricane Hilda of 1955 and Hurricane Charley of 1951, but Karl is by far the farthest south a major hurricane has been in the Gulf of Mexico. Hurricane records go back to 1851, but Karl is a small storm and could have gotten missed as being a major hurricane before the age of aircraft reconnaissance (1945).


Figure 1. Tracks of all major hurricanes since 1851 near Mexico's Bay of Campeche. Karl is most southerly major hurricane on record in the Gulf of Mexico. Image credit: NOAA Coastal Services Center.

With Karl's ascension to major hurricane status, we are now ahead of the pace of the terrible hurricane seasons of 2004 and 2005 for number of major hurricanes so early in the year. In 2005, the fifth major hurricane (Rita) did not occur until September 21, and in 2004, the fifth major hurricane (Karl) arrived on September 19. Wunderblogger Cotillion has put together a nice page showing all the seasons with five or more major hurricanes. The last time we had five major hurricanes earlier in the season was in 1961, when the fifth major hurricane (Esther) arrived on September 13. This morning we continue to have three simultaneous hurricanes, Hurricanes Igor, Julia, and Karl. This is a rare phenomena, having occurred only eight previous years since 1851. The last time we had three simultaneous hurricanes in the Atlantic was in 1998. That year also had four simultaneous hurricanes--Georges, Ivan, Jeanne and Karl--for a brief time on September 25. There has been just one other case of four simultaneous Atlantic hurricanes, on August 22, 1893. The year 2005 came within six hours of having three hurricanes at the same time, but the official data base constructed after the season was over indicates that the three hurricanes did not exist simultaneously.

Also remarkable this year is that are seeing major hurricanes in rare or unprecedented locations. Julia was the easternmost major hurricane on record, Karl is the most southerly major hurricane on record in the Gulf of Mexico, and Earl was the 4th strongest hurricane so far north. This unusual major hurricane activity is likely due, in part, to the record Atlantic sea surface temperatures this year.


Figure 2. Triple trouble, day two: From left to right, Hurricanes Karl, Igor, and Julia roil the Atlantic at 9:45 am EDT, September 17, 2010. Image credit: NASA/GSFC.

Karl
Hurricane Karl put on a burst of intensification this morning unprecedented in this part of the Atlantic, bottoming out as a Category 3 hurricane with a 957 mb pressure and winds of 120 mph. Karl's pressure dropped 10 mb between 1am EDT and 7 am EDT, but the pressure during the Hurricane Hunters' latest pass through the eye, at 10:12 am, had risen 12 mb, likely indicating that Karl's winds may weaken quickly in the next few hours. Karl is getting very close to land, and interaction with land will probably limit further intensification. Mexican radar out of Alvarado shows the eye is very close to the coast.


Figure 3. Radar image of Karl approaching landfall in Mexico. Image credit: Mexican Weather Service.

Impact of Karl on Mexico
Given that the Bay of Campeche coast has never experienced a hurricane as strong as Karl, its impact is likely to cause unprecedented damage to a 50-mile wide coastal area between Veracruz and Poza Rica. The strongest hurricanes in history to affect the region were Item in 1950, with 110 mph winds, Janet in 1955, with 100 mph winds, and Diana of 1990, with 100 mph winds. Flooding from Janet killed over 800 people in Mexico. and flooding from Diana killed at least 139 people. Fortunately, the Mexicans have one of the best disaster preparedness programs in the world, and it is likely that evacuations from the storm surge zone of Karl will greatly limit the loss of life from storm surge. The section of coast expected to receive Karl's maximum 12 - 16 foot storm surge is moderately populated, but is low-lying only in limited regions. Of greatest concern are Karl's torrential rains, since the region has high mountains near the coast that will experience extreme rainfall and flooding. Karl's high winds are also a major concern, and these winds are likely to damage thousands of buildings near the coast.

Igor
Hurricane Igor has slowly weakened over the past day, but remains a large and dangerous Category 3 hurricane with 120 mph winds. Igor passed just north of buoy 41044 last night, and the buoy recorded a lowest pressure of 942 mb. Top winds during Igor's passage were sustained at 74 mph, but this reading was on the weak left front side of the hurricane. The buoy recorded a significant wave height of 38 feet (the significant wave height is the average of the highest 1/3 of the waves.)


Figure 4. Morning satellite image of Igor.

Intensity forecast for Igor
Wind shear is low to moderate, 5 - 15 knots, and is expected to remain in this range through Saturday afternoon. Waters are warm, 29°C, and will remain 29°C through Saturday morning, then slowly decline. Igor is well armored against any intrusions of dry air for at least the next two days. These conditions should allow Igor to remain at major hurricane status through Saturday afternoon. It is possible the hurricane will undergo another eyewall replacement cycle, where the eyewall collapses and a new eyewall forms from an outer spiral band. This will weaken the hurricane by 10 - 20 mph if it occurs, but Igor may regain its lost intensity once the cycle is over, as it has done after its previous two eyewall replacement cycles. By Saturday afternoon, the trough of low pressure steering Igor northwestwards should bring moderate wind shear of 10 - 20 knots to the storm, potentially weakening it. The SHIPS models predicts shear will not rise to the high range, 20 - 30 knots, until the hurricane reaches the island, which may be soon enough to induce substantial weakening by perhaps 20 - 30 mph before Igor arrives at Bermuda. Igor will still probably be at least a Category 2 hurricane on its closest pass by Bermuda on Sunday night, and perhaps a Category 3. NHC is giving Bermuda a 29% chance of experiencing hurricane force winds from Igor, but this probability is likely too low. The Bermuda Weather Service is calling for Category 2 hurricane conditions for the island on Sunday, with 20 - 40 foot waves in the offshore waters, and 6 - 12 foot seas in the inland waters.

Igor's impact on Bermuda
The track forecast for Igor remains unchanged. Igor is moving northwest, in response to the steering influence of a broad trough of low pressure moving across the Western Atlantic. This trough will steer Igor to the northwest and north over the next three days, bringing the core of the storm very close to Bermuda late Sunday night. Igor is a huge storm, and tropical storm force winds extend out 290 miles to the north of its center. As the hurricane moves north, it will expand in size, as it takes advantage of the extra spin available at higher latitudes due to Earth's rotation. By Saturday night, Igor's tropical storm force winds are expected to extend outwards 320 miles from the center. Igor will be moving at about 11 - 13 mph during the final 24 hours of its approach to Bermuda, so the island can expect a period of 39+ mph tropical storm force winds to begin near midnight Saturday night--a full 24 hours before the core of Igor arrives. Igor will speed up to about 15 mph as it passes the island near midnight Sunday night, and Bermuda's battering by tropical storm force winds will not be as long as Igor moves away, perhaps 10 hours long. Hurricane force winds will probably extend out about 60 miles from the center when the core of Igor reaches Bermuda, and the island can expect to be pounded by hurricane force winds for up to 6 - 8 hours. In all, Bermuda is likely to suffer a remarkably long 36-hour period of tropical storm force winds, with the potential for many hours of hurricane force winds. Long duration poundings like this are very stressful for buildings, and there is the potential for significant damage on Bermuda. However, buildings in Bermuda are some of the best-constructed in the world, and damage on the island will be much lower than might otherwise be expected.

Bermuda's hurricane history
Igor is similar in strength and projected track to Hurricane Fabian of 2003. Fabian hit Bermuda as a Category 3 hurricane with 120 mph winds. It was the most damaging hurricane ever to hit the island, with $355 million in damage. Fabian's storm surge killed four people crossing a causeway on the island. These were the first hurricane deaths on Bermuda since 1926. The most powerful hurricane on record to strike Bermuda was the Category 4 Havana-Bermuda Hurricane, which hit on October 22, 1926, with 135 mph winds. The hurricane sank two British warships, claiming 88 lives, but no one was killed on the island. The deadliest hurricane to affect the island occurred on September 12, 1839, when a Category 3 hurricane with 125 mph winds and an 11-foot storm surge hit, tearing off the roofs of hundreds of buildings and wrecking several ships. An estimated 100 people were killed (source: Encyclopedia of Hurricanes, Typhoons, and Cyclones, by David Longshore.)

Igor's impact on the rest of the Atlantic
The models have been in substantial agreement over multiple runs that Igor will miss the U.S. and Canadian coasts--with the possible exception of southeast Newfoundland, which the ECMWF model predicts could see a close pass by Igor. The chief danger to the U.S. and Canada will come in the form of high waves. Large swells from Igor are pounding the Bahamas, Puerto Rico, and the Northern Lesser Antilles Islands, and will spread westwards to the U.S. East Coast today. By Saturday, much of the East Coast from northern Florida to Cape Cod Massachusetts can expect waves of 3 - 4 meters (10 - 13 feet), causing dangerous rip currents and significant beach erosion. These waves will continue through Sunday then gradually die down. The latest NOAA marine forecast for Cape Hatteras, North Carolina calls for 6 - 11 foot waves on Saturday night, and 9 - 13 foot waves on Sunday.

Julia
Strong upper level winds from big brother Igor are creating a high 20 - 30 knots of shear over Hurricane Julia this morning, and the hurricane is destined to weaken to a tropical storm soon. The high shear has eroded away the northwestern portion of Julia's heavy thunderstorms, and should be strong enough to destroy Julia by early next week. Julia is not expected to threaten any land areas.

Unusually quiet in the Pacific
The unusually quiet Western Pacific typhoon season has its 11th named storm of the season, Typhoon Fanapi. Fanapi, a Category 1 storm, is located 400 miles east of Taiwan, and is expected to intensify into a Category 2 storm before making landfall on the island Sunday. Ordinarily, the Western Pacific should be up to seventeen named storms by now. It has also been unusually quiet in the Eastern Pacific. On average, that ocean basin should have had 11 named storms, 6 hurricanes, and 2 intense hurricanes by now. This season, we've had about half the normal activity--just 6 named storms, 3 hurricanes, and 1 intense hurricane.

Elsewhere in the tropics
The ECMWF model develops a new tropical depression a few hundred miles off the coast of Africa 4 - 5 days from now. The GFS and NOGAPS models have backed off on their predictions of a Caribbean development late next week.

I'll have an update this afternoon.

Jeff Masters

Hurricane

A rare triple threat: three simultaneous Atlantic hurricanes

By: JeffMasters, 8:47 PM GMT on September 16, 2010

For the first time in twelve years, we have a rare triple threat in the Atlantic--three simultaneous hurricanes. Hurricane Karl joined Hurricanes Igor and Julia in the steadily expanding Hurricanes of 2010 club this morning, becoming the sixth hurricane of the season. The last time we had three simultaneous hurricanes in the Atlantic was in 1998. That year also had four simultaneous hurricanes--Georges, Ivan, Jeanne and Karl--for a brief time on September 25. There has been just one other case of four simultaneous Atlantic hurricanes, on August 22, 1893. According to Phil Klotzbach at Colorado State, three simultaneous Atlantic hurricanes is a rare phenomena, having occurred only eight other times since 1851. The other years were 1893, 1926, 1950, 1961, 1967, 1980, 1995, and 1998.


Figure 1. Triple trouble: From left to right, Hurricanes Karl, Igor, and Julia roil the Atlantic. Image credit: NASA/GSFC.

Karl
Hurricane Karl continues to intensify. The latest Hurricane Hunter flight, flying at 12,000 feet, found flight level winds of 95 mph. This suggests surface winds of 85 mph, though the top surface winds seen by their SFMR instrument were about 80 mph. Mexican radar out of Alvarado shows the outer spirals bands of Karl are dumping heavy rains on the Mexican coast along the Bay of Campeche.


Figure 2. Afternoon radar image from the Alvarado, Mexico radar. The eye of Karl is visible in the upper right, and rain bands are affecting the coast to the east of the radar site. Image credit: Mexican Weather Service..

Forecast for Karl
Conditions for intensification are ideal in the Gulf of Mexico's Bay of Campeche, with wind shear expected to be low, 5 - 10 knots, SSTs warm, 29°C - 30°C, and the atmosphere very moist. These conditions, combined with the topography of the surrounding coast which tends to enhance counter-clockwise flow, should allow Karl to intensify into Category 2 hurricane before making landfall between Tampico and Vercruz, Mexico Friday afternoon. Karl is a small storm, and is unlikely to bring any rain or wind to Texas.

Igor
The Air Force Hurricane Hunters made their first foray into Hurricane Igor this afternoon, and found a high-end Category 3 storm, with a central pressure of 940 mb and top winds at 10,000 feet of 150 mph. The southwest portion of the eyewall was open, so Igor has the potential to intensify once again if it can close off the gap. There are no major changes to the track or intensify forecast for Igor in the latest set of model runs. Igor is expected to remain a major hurricane for the next two days, and is headed northwest at 7 mph. This motion will carry the core of the hurricane close to NOAA buoy 41044 between 9 - 11 pm EDT tonight. Top winds at the buoy so far today have been 65 mph, gusting to 81 mph, with a significant wave height of 38 feet (the significant wave height is the average of the highest 1/3 of the waves.)

Elsewhere in the tropics
The ECMWF model develops a new tropical depression a few hundred miles off the coast of Africa 2 - 4 days from now. The GFS is suggesting the eastern Caribbean could see a tropical depression 6 - 7 days from now.

I'll have an update Friday morning.

Jeff Masters

Hurricane

Karl near hurricane strength; Igor intensifying again

By: JeffMasters, 2:00 PM GMT on September 16, 2010

Tropical Storm Karl is back over water after popping off the coast of Mexico's Yucatan Peninsula early this morning. Despite being a small storm, Karl managed to keep a remarkable degree of organization during its crossing of the Yucatan. Karl has already regained all of its lost strength, and is near hurricane intensity. A Hurricane Hunter aircraft is currently in Karl, and at 8:47am EDT found winds at 5,000 feet of 85 mph, which suggest winds near 65 - 70 mph were occurring at the surface. The aircraft noted that Karl had built an eyewall that was open on the north-northeast side. The eye is now apparent in both visible and infrared satellite imagery. Mexican radar out of Alvarado shows the outer spirals bands of Karl are approaching the coast near Veracruz, and heavy rains of 2 - 4 inches can be expected today along much of Mexico's Bay of Campeche coast.


Figure 1. Image from NASA's Terra satellite taken at 12:40pm EDT Wednesday September 15, 2010 of Tropical Storm Karl over the Yucatan Peninsula. Image credit: NASA.

Forecast for Karl
Conditions for intensification are ideal in the Gulf of Mexico's Bay of Campeche, with wind shear expected to be low, 5 - 10 knots, SSTs warm, 29°C - 30°C, and the atmosphere very moist. These conditions, combined with the topography of the surrounding coast which tends to enhance counter-clockwise flow, should allow Karl to intensify into a Category 2 hurricane before making landfall between Tampico and Vercruz, Mexico Friday morning. NHC is giving Karl a 7% chance of reaching Category 3 strength, but the recent data from the Hurricane Hunters suggest that these odds are higher, perhaps 30%. The 06Z (2 am EDT) run of the GFDL model makes Karl a strong Category 2 hurricane with 105 - 110 mph winds at landfall Friday, and this is a reasonable forecast. Karl is a small storm, and is unlikely to bring any rain or wind to Texas.


Figure 2. Forecast swath of maximum winds from Karl, as predicted by the GFDL model on its 2am EDT (6Z) run this morning. The GFDL is predicting a 50-mile wide stretch of the Mexican coast will receive Category 1 (yellow colors, 64+ knots) or Category 2 (orange colors, 83+ knots) winds. Image credit: Morris Bender, NOAA/GFDL.

Igor
Hurricane Igor completed an eyewall replacement cycle early this morning, and has been intensifying. Igor is headed west-northwest to northwest at 7 mph, and this motion will carry the core of the hurricane close to NOAA buoy 41044 between 9 - 11 pm EDT tonight. Top winds at the buoy so far today have been 52 mph, gusting to 65, with a significant wave height of 32 feet (the significant wave height is the average height of the highest 1/3 of the waves.) The Hurricane Hunters are scheduled to make their first flight into Igor this afternoon, and we will see then exactly how strong Igor is. Satellite imagery shows that Igor looks a bit ragged on its north side, but the northern eyewall is getting stronger, and the eye is clearing out and contracting--signs of strengthening.


Figure 3. Morning satellite image of Igor.

Intensity forecast for Igor
Wind shear is low to moderate, 5 - 15 knots, and is expected to remain in this range through Saturday morning. Waters are warm, 29°C, and will remain 29°C through Saturday morning. Igor is well armored against any intrusions of dry air for at least the next two days. These conditions should allow Igor to remain at major hurricane status through Saturday afternoon. It is possible the hurricane will undergo another eyewall replacement cycle on Friday or Saturday, where the eyewall collapses and a new eyewall forms from an outer spiral band. This will weaken the hurricane by 10 - 20 mph if it occurs, but Igor may regain its lost intensity once the cycle is over, as it has done after the two eyewall replacement cycles it has already undergone. By Saturday morning, 36 hours before the core of Igor is expected to pass Bermuda's latitude, the trough of low pressure steering Igor northwestwards should bring moderate wind shear of 10 - 20 knots to the storm, potentially weakening Igor. The SHIPS models predicts shear will not rise to the high range, 20 - 30 knots, until after the hurricane reaches the island. Igor will also be tracking over cooler 28°C waters during this period, and substantial weakening by perhaps 20 - 30 mph can be expected about the time Igor arrives at Bermuda. Igor will still probably be at least a Category 2 hurricane on its closest pass by Bermuda on Sunday night, and perhaps a Category 3 storm. NHC is giving Bermuda a 21% chance of experiencing hurricane force winds from Igor, but this probability is likely too low. The Bermuda Weather Service is calling for Category 1 or 2 hurricane conditions for the island on Sunday, with 20 - 30 foot waves in the offshore waters.

Igor's impact on Bermuda
The track forecast for Igor remains unchanged. Igor is moving west-northwest, in response to the steering influence of a broad trough of low pressure moving across the Western Atlantic. This trough will steer Igor to the northwest and north over the next three days, bringing the core of the storm very close to Bermuda late Sunday night. Igor is a huge storm, and tropical storm force winds extend out 270 miles to the north of its center. As the hurricane moves north, it will expand in size, as it takes advantage of the extra spin available at higher latitudes due to Earth's rotation. By Saturday night, Igor's tropical storm force winds are expected to extend outwards 310 miles from the center. Igor will be moving at about 11 - 13 mph during the final 24 hours of its approach to Bermuda, so that island can expect a period of 39+ mph tropical storm force winds to begin near midnight Saturday night--a full 24 hours before the core of Igor arrives. Igor will speed up to about 15 mph as it passes Bermuda near midnight Sunday night. Hurricane force winds will probably extend out about 60 miles from the center then, and the island can expect to be pounded by hurricane force winds for up to 6 - 8 hours if the core of the hurricane tracks over the island. In all, Bermuda is likely to suffer a remarkably long 36-hour period of tropical storm force winds, with the potential for many hours of hurricane force winds. Long-duration poundings like this are very stressful for buildings, and there is the potential for significant damage on Bermuda.

Igor's impact on the rest of the Atlantic
The models have been in substantial agreement over multiple runs that Igor will miss the U.S. and Canadian coasts--with the possible exception of southeast Newfoundland, which the ECMWF model predicts could see a close pass by Igor. The chief danger to the U.S. and Canada will come in the form of high waves. Large swells from Igor have arrived in the Northern Lesser Antilles Islands and Puerto Rico, and will spread westwards over the next few days. By Saturday, much of the East Coast from northern Florida to Cape Cod Massachusetts can expect waves of 3 - 4 meters (10 - 13 feet), causing dangerous rip currents and significant beach erosion. These waves will continue through Sunday then gradually die down. The latest NOAA marine forecast for Cape Hatteras, North Carolina calls for 7 - 10 foot waves on Saturday, and 9 - 13 foot waves on Sunday.

Julia
Hurricane Julia put on a remarkable and unexpected burst of intensification yesterday morning to become the season's fourth Category 4 storm, but is now on a long steadily decline in intensity. The hurricane is currently over waters right at the lower limit for maintaining a hurricane, 26.5°C (80°F), and is undergoing high shear of 20 - 25 knots. While the shear will abate tonight and the water will warm some, Julia is headed towards some very hostile upper-level winds beginning on Friday. These strong winds, courtesy of the upper level outflow from Hurricane Igor, will bring 30 - 45 knots of wind shear to Julia Friday night through Sunday. The high shear should be enough to rapidly weaken Julia over the weekend. Julia is not expected to threaten any land areas.

Elsewhere in the tropics
The ECMWF model develops a new tropical depression a few hundred miles off the coast of Africa 2 - 4 days from now. The GFS and NOGAPS models are suggesting the eastern Caribbean could see a strong tropical disturbance form 6 - 7 days from now.

I'll have an update this afternoon.

Jeff Masters

Hurricane

Karl hits the Yucatan; two simultaneous Cat 4s in the Atlantic for 2nd time in history

By: JeffMasters, 2:37 PM GMT on September 15, 2010

The Atlantic hurricane season of 2010 kicked into high gear this morning, with the landfall of Tropical Storm Karl in Mexico, and the simultaneous presence of two Category 4 hurricanes in the Atlantic, Igor and Julia. Tropical Storm Karl's formation yesterday marked the fifth earliest date that an eleventh named storm of the season has formed. The only years more active this early in the season were 2005, 1995, 1936 and 1933. This morning's unexpected intensification of Hurricane Julia into a Category 4 storm with 135 mph winds has set a new record--Julia is now the strongest hurricane on record so far east. When one considers that earlier this year, Hurricane Earl became the fourth strongest hurricane so far north, it appears that this year's record SSTs have significantly expanded the area over which major hurricanes can exist over the Atlantic. This morning is just the second time in recorded history that two simultaneous Category 4 or stronger storms have occurred in the Atlantic. The only other occurrence was on 06 UTC September 16, 1926, when the Great Miami Hurricane and Hurricane Four were both Category 4 storms for a six-hour period. The were also two years, 1999 and 1958, when we missed having two simultaneous Category 4 hurricanes by six hours. Julia's ascension to Category 4 status makes it the 4th Category 4 storm of the year. Only two other seasons have had as many as five Category 4 or stronger storms (2005 and 1999), so 2010 ranks in 3rd place in this statistic. This year is also the earliest a fourth Category 4 or stronger storm has formed (though the fourth Category 4 of 1999, Hurricane Gert, formed just 3 hours later on today's date in 1999.) We've also had four Cat 4+ storms in just twenty days, which beats the previous record for shortest time span for four Cat 4+ storms to appear. The previous record was 1999, 24 days (thanks to Phil Klozbach of CSU for this stat.)


Figure 1. A rare double feature: two simultaneous Category 4 hurricanes in the Atlantic, for only the second time in recorded history.

Karl
Tropical Storm Karl made landfall as a strong tropical storm with 65 mph winds and a central pressure of 991 mb at 8:45am EDT this morning on Mexico's Yucatan Peninsula, just north of the Belize border. Karl took advantage of nearly ideal conditions for intensification, and in just fifteen hours intensified from a tropical disturbance to a strong tropical storm with 65 mph winds. Had Karl managed to get its act together just one day earlier, it could have been a major hurricane at landfall this morning. Fortunately, Karl has a relatively small area of strong winds--tropical storm force winds extend out just 45 miles from the center of the storm, and wind damage is not the main concern. Heavy rains are the main concern, and Belize radar shows heavy rain bands from Karl spreading ashore over northern Belize near the border with Mexico. Cancun radar shows that heavy rains are relatively limited, though, near the tourist havens of Cancun and Cozumel.


Figure 2. Radar image of Karl at landfall this morning near the northern Belize/Mexican border. Image credit: Belize National Meteorological Service.

Forecast for Karl
Karl will traverse the Yucatan Peninsula today and emerge into the Gulf of Mexico's Bay of Campeche Thursday morning as a much weakened tropical storm, with perhaps 40 - 45 mph top winds. Once in the Gulf, conditions for intensification are ideal, with wind shear is expected to be low, 5 - 10 knots, SSTs will be warm, 29°C - 30°C, and the atmosphere very moist. These conditions, combined with the topography of the surrounding coast which tends to enhance counter-clockwise flow, should allow Karl to intensify into a strong tropical storm or a Category 1 hurricane before making landfall between Tampico and Vercruz, Mexico on Saturday morning. However, since Karl is a small storm, it is possible that passage over the Yucatan will disrupt the storm enough so that it will be much weaker. The ridge of high pressure steering Karl westwards is quite strong, and it is very unlikely that the storm will turn northwest and hit Texas. NHC is giving Brownsville, Texas, an 10% chance of receiving tropical storm force winds of 39+ mph.

Igor
Hurricane Igor put on a burst of intensification last night to put it at its strongest yet, a top-end Category 4 hurricane with 155 mph winds. Igor has weakened slightly this morning, but remains a formidable presence in the Central Atlantic with its 145 mph winds. Igor continues to show the classic appearance of a major hurricane on satellite imagery, with a well-formed eye, symmetrical cloud pattern, plenty of low-level spiral bands, and solid upper-level outflow on all sides.


Figure 3. Hurricane Igor as captured at 18 UTC Tuesday September 14, 2010, from the International Space Station. Image credit: Douglas Wheelock, NASA.

Intensity forecast for Igor
Wind shear is low, 5 - 10 knots, and is expected to remain low for the next 2 - 3 days. Waters are warm, 29°C, and will remain 29°C for the next 2 - 3 days. Igor is well armored against any intrusions of dry air for at least the next three days. These conditions should allow Igor to remain at major hurricane status for the next three days. The hurricane will probably undergo one of the usual eyewall replacement cycles intense hurricanes commonly have, where the eyewall collapses and a new eyewall forms from an outer spiral band. This will weaken the hurricane by 10 - 20 mph when it occurs, and may be responsible for the 10 mph weakening Igor experienced early this morning. Igor may regain its lost intensity over the next 36 hours. By Saturday morning, 36 hours before the core of Igor is expected to pass Bermuda's latitude, the trough of low pressure steering Igor northwestwards should bring moderate wind shear of 10 - 20 knots to the storm, weakening it. The SHIPS models predicts shear will rise to the high range, 20 - 30 knots, during the final 24 hours of the storm's approach to Bermuda. Igor will also be tracking over cooler 28°C waters during this period, and substantial weakening by perhaps 20 - 30 mph can be expected. Igor will still probably be at least a Category 2 hurricane on its closest pass by Bermuda on Sunday. NHC is giving Bermuda a 13% chance of experiencing hurricane force winds from Igor, but this probability is likely too low. The Bermuda Weather Service is calling for Category 1 or 2 hurricane conditions for the island on Sunday, with 20 - 25 foot waves in the offshore waters.

Track forecast for Igor
The track forecast for Igor remains unchanged. Igor has made its long-anticipated turn to the west-northwest, in response to the steering influence of a broad trough of low pressure moving across the Western Atlantic. This trough will steer Igor several hundred miles to the northeast of the Lesser Antilles, and high waves should be the only impact of Igor on the islands. Igor appears likely to be a threat to Bermuda, and that island can expect tropical storm force winds as early as Saturday. Igor will be moving at about 12 - 15 mph as it approaches Bermuda. Tropical storm force winds of 39+ mph will probably extend out about 250 miles to the north of Igor on Saturday, so Bermuda can expect 18 hours of tropical storm force winds before the core of Igor makes its closest pass. In all, Bermuda is likely to experience a very long pounding of 24 - 36 hours with winds in excess of tropical storm force.

The models have been in substantial agreement over multiple runs that Igor will miss the U.S. East Coast, and the danger to the U.S. will probably only come in the form of high waves. Large swells from Igor have arrived in the Northern Lesser Antilles Islands, and will spread westwards over the next few days, reaching the U.S. East Coast on Friday. By Saturday, much of the East Coast from northern Florida to Cape Cod Massachusetts can expect waves of 3 - 4 meters (10 - 13 feet), causing dangerous rip currents and significant beach erosion. These waves will continue through Sunday then gradually die down. The latest NOAA marine forecast for Cape Hatteras, North Carolina calls for 8 - 10 foot waves on Saturday, and 9 - 12 foot waves on Sunday.

Igor may pass very close to Newfoundland, Canada, but it is too early too assess the likelihood of this happening.

Julia
Hurricane Julia put on a remarkable and unexpected burst of intensification this morning to become the season's fourth Category 4 storm. Julia's 135 mph winds make it the strongest hurricane on record so far east; the previous record was held by the eighth storm of 1926 which was only a 120 mph Category 3 hurricane at Julia's current longitude. Julia's intensification was a surprise, since SSTs in the region are about 27.5°C, which is just 1°C above the threshold needed to sustain a Category 1 hurricane. Julia is headed northwest, out to sea, and it is unlikely that this storm will trouble any land areas. SSTs will steadily cool to 26.5°C today, and further intensification today is unlikely. Shear will be moderate, 10 - 20 knots, over Julia during the next two days, then rise sharply to 30 knots 3 - 5 days from now, as Julia moves within 1000 miles of Igor and begins to experience strong northwesterly winds from her big brother's upper level outflow. This should substantially weaken Julia.

Elsewhere in the tropics
The GFS and ECMWF models develop a new tropical depression a few hundred miles off the coast of Africa 3 - 6 days from now. The GFS also develops a tropical depression in the eastern Caribbean 6 - 7 days from now.

Portlight's 2-year anniversary
On September 14, 2008, the devastation wrought by Hurricane Ike on Texas and Louisiana moved members of the wunderground community to put into action their own impromptu relief effort. From this humble beginning has grown a disaster-relief charity I have been proud to support--Portlight.org. We've been blessed this hurricane season with relatively few landfalling storms, so Portlight's new disaster relief trailer (Figure 4), financed with a $21,500 grant from the Christopher and Dana Reeve Foundation, has yet to be deployed. With five weeks of peak hurricane season still to come, the new trailer may yet get a call to action. The mobile kitchen in the trailer will be able to feed several hundred people per day, and the trailer is equipped with portable ramps to help with shelter accessibility, as well as durable medical equipment to facilitate mobility and independence for survivors. The trailer is mobile, and Portlight is willing to load it up and fly it to Bermuda, if Igor ends up making a mess there!

The lack of landfalling storms has allowed Portlight to continue to concentrate their efforts on Haiti, where their assistance has been a tremendous boost for those most in need, the disabled. Portlight is working on constructing steel shelters out of shipping containers for homeless Haitians, as detailed in the Haitian Relief Recap blog post. Please visit the Portlight.org web site or the Portlight blog to learn more and donate. A few other items of note:

Portlight has been able to facilitate providing assistance to people with disabilities in Pakistan, where the worst natural disaster in their history has left 4 million homeless. While not directly involved in delivering relief, Portlight has been able to connect local Disabled People's Organizations with important sources of food, water, filtration systems, and medical equipment.

ABC News4 in Charleston broadcast a story about the Portlight relief trailer, and Portlight has also been featured on the Pacifica Radio Network.

Portlight launched a quarterly newsletter, The Portlight View, which can be seen on the newly redesigned website.


Figure 4. The new Portlight disaster relief trailer, funded by their $21,500 grant from the Christopher and Dana Reeve foundation.

I'll have an update Thursday morning.

Jeff Masters

Hurricane

Igor turns west-northwest; Julia a hurricane; 92L growing more organized

By: JeffMasters, 1:49 PM GMT on September 14, 2010

Hurricane Igor remains an impressive Category 4 hurricane with 135 mph winds over the Central Atlantic. Though Igor's winds are 15 mph weaker than at its 150 mph peak yesterday, the hurricane continues to maintain the classic appearance of a major hurricane on satellite imagery, with a well-formed eye, plenty of low-level spiral bands, and solid upper-level outflow to the north and south.


Figure 1. Hurricane Igor as seen by the MODIS instrument on NASA's Aqua satellite at 12:40 pm EDT Monday, September 13, 2010. Image credit: NASA.

Intensity forecast for Igor
Wind shear is low, 5 - 10 knots, and is expected to remain low for the next 3 - 4 days. Waters are warm, 28.7°C, and will warm to 29°C by Wednesday. Igor has moistened its environment enough to keep the dry air of the Saharan Air Layer (SAL) at bay. These conditions should allow Igor to remain at major hurricane status for the next 3 - 4 days. The hurricane will probably undergo one of the usual eyewall replacement cycles intense hurricanes commonly have, where the eyewall collapses and a new eyewall forms from an outer spiral band. This will weaken the hurricane by 10 - 20 mph when it occurs, and may be responsible for the 15 mph weakening Igor experienced since yesterday. Igor will probably regain its lost intensity when the cycle completes in the 12 - 36 hours. By Saturday, when Igor should be nearing Bermuda, the trough of low pressure steering Igor northwestwards should bring moderate wind shear of 10 - 20 knots to the storm, weakening it. Igor will also be tracking over cooler 28°C waters then.

Track forecast for Igor
The track forecast for Igor remains unchanged. Igor has made its long-anticipated turn to the west-northwest, in response to the steering influence of a broad trough of low pressure moving across the Western Atlantic. This trough will steer Igor several hundred miles to the northeast of the Lesser Antilles, and high waves should be the only impact of Igor on the islands. In the longer range, Igor appears likely to be a threat to Bermuda, and that island can expect tropical storm force winds as early as Friday. Igor does have a small chance of making landfall on the U.S. East Coast or Canada. Climatology shows that about 20% of all tropical cyclones that have existed at Igor's current position have gone on to hit the U.S. East Coast; these odds are about 5 - 10% for Bermuda and 15% for Canada. The forecast steering current pattern for the period 5 - 10 days from now from the ECMWF and GFS models shows several modest troughs of low pressure moving across the Western Atlantic. These troughs will probably be strong enough to recurve Igor out sea. However, 5 - 10 day forecasts are prone to large errors, and it is too early to be highly confident that Igor will miss hitting the U.S. or Canadian coasts.

Wave forecast for Igor
Large swells from Igor have arrived in the Northern Lesser Antilles Islands, and will spread westwards over the next few days, reaching the U.S. East Coast on Friday. By Saturday, much of the East Coast from northern Florida to Cape Cod Massachusetts can expect waves of 3 - 4 meters (10 - 13 feet), causing dangerous rip currents and significant beach erosion. These waves will continue through Sunday then gradually die down. The latest NOAA marine forecast for Cape Hatteras, North Carolina calls for 8 - 11 foot waves on Saturday.


Figure 3. Forecast wave heights for 2pm EDT Saturday September 18, 2010, as predicted by 00 UTC 9/14/2010 run of NOAA's Wavewatch III model.

Caribbean disturbance 92L
Tropical disturbance 92L over the Western Caribbean, between Jamaica and the Yucatan Peninsula, has become more organized this morning. The storm remains a threat to develop into a tropical depression, but time is running out for it to do so. There is no evidence of a surface circulation on satellite loops this morning, but the cloud pattern of 92L has become more circular, with low-level spiral bands developing on the west and north sides of the storm. 92L has a moderate but increasing area of intense thunderstorms; these are bringing heavy rains to Jamaica, the Cayman Islands, and western Cuba this morning.


Figure 3. Morning satellite image of 92L.

Forecast for 92L
Rains from 92L will spread over Belize, Northern Guatemala, and Mexico's Yucatan Peninsula tonight through Wednesday, bringing peak accumulations in the 4 - 8 inch range. Lesser peak amounts of 2 - 4 inches are possible over northern Honduras. Wind shear over 92L is low, 5 - 10 knots, and is expected to remain low for the next five days. The waters beneath are hot, 29.7°C, and these warm waters extend to great depth. Water vapor satellite loops show a large area of dry air lies to the north and west of 92L; this dry air has been interfering with development of 92L, and will continue to do so. NHC is putting the odds of 92L developing into a tropical depression by Thursday at 40%; I'll give it a 50% chance. Given the current disorganized state of 92L, it would be difficult for it to intensify quickly enough to become any stronger than a tropical storm with 50 mph winds by Wednesday afternoon, when it will move over Belize and Mexico's Yucatan Peninsula. Once 92L crosses the Yucatan, the ridge of high pressure steering it is expected to remain in place, forcing 92L west or west-southwest to a second landfall in Mexico between Veracruz and Poza Rica early Saturday morning. The shape of Mexico's Bay of Campeche and the topography of the mountains surrounding the Bay help air spiral in a counterclockwise fashion, aiding tropical storm development, and 92L has its best chance of development once it crosses into the Bay of Campeche. With the shear there expected to be low and the waters warm, I give a high 70% chance that 92L will be a tropical depression or tropical storm in the Bay of Campeche. The GFDL model is predicting 92L could be a hurricane at landfall near Veracruz on Saturday morning; the other intensity models are much less aggressive. Given the rapid development of Hermine in a similar location last week, residents of the Mexican Gulf Coast should be wary of the possibility that 92L could intensify into at least a strong tropical storm before making landfall Friday night or Saturday morning. A Hurricane Hunter aircraft is scheduled to investigate 92L this afternoon.

Julia
Hurricane Julia is headed northwest, out to sea, and it is unlikely that this storm will trouble any land areas. The intensification of Julia into a hurricane brings our activity tally for the 2010 Atlantic hurricane season to 10 named storms, 5 hurricanes, and 3 intense hurricanes. An average season has 10 named storms, 6 hurricanes, and 2 intense hurricanes, so we've already had a full season's worth of activity, with about 45% of the season still to come.

Shear will be low to moderate, 5 - 20 knots, over Julia during the next two days. Shear will rise sharply to 30 knots 3 - 5 days from now, as Julia moves within 1000 miles of Igor and begins to experience strong northwesterly winds from her big brother's upper level outflow. Julia does have a window of opportunity today and Wednesday to intensify into a Category 2 hurricane before the shear rises.

Elsewhere in the tropics
The GFS and ECMWF models are suggesting the possibility of a new tropical depression forming a few hundred miles off the coast of Africa about seven days from now.

"Hurricane Haven" airing this afternoon
Tune in to my live Internet radio show, "Hurricane Haven", airing at 4pm EDT today. If you want to ask a question, the call in number is 415-983-2634, or you can email a question to broadcast@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line.

Today's show will be about 30 minutes, and you can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml. The show will be recorded and stored as a podcast.

Next post
I'll have a new post on Wednesday morning.

Jeff Masters

Hurricane

Igor an impressive Cat 4; 92L running out of time to develop; Julia forms

By: JeffMasters, 1:47 PM GMT on September 13, 2010

There are few sights in the natural world more impressive than a hurricane near maximum intensity. Hurricane Igor certainly fits that description this morning, as it flirts with Category 5 strength in the Central Atlantic. Igor's rapid intensification burst brought the mighty hurricane's winds to 150 mph, just shy of the 156 mph threshold for Category 5 status. Igor is the strongest hurricane in the Atlantic in three years. The last hurricane stronger that Igor was Category 5 Hurricane Felix of 2007.


Figure 1. Morning satellite image of Igor.

Intensity forecast for Igor
Wind shear is low, 5 - 10 knots, and is expected to remain low for the next four days. Waters are warm, 28.5°C, and will warm to 29°C by Wednesday. Igor has moistened its environment enough to keep the dry air of the Saharan Air Layer (SAL) at bay. These conditions should allow Igor to remain at major hurricane status for the next four days. The hurricane will probably undergo one of the usual eyewall replacement cycles intense hurricanes commonly have, where the eyewall collapses and a new eyewall forms from an outer spiral band. This will weaken the hurricane by 10 - 20 mph when it occurs, but Igor will probably regain its lost intensity when the cycle completes. There's no evidence that an eyewall replacement cycle is imminent today, so Igor could potentially strengthen a bit more. However, I believe Igor has peaked, and will not reach Category 5 status today. By Saturday, when Igor should be nearing Bermuda, the trough of low pressure steering Igor northwestwards should bring moderate wind shear of 10 - 20 knots to the storm, weakening it.

Track forecast for Igor
The track forecast for Igor remains unchanged. Igor will move west under the influence of a strong ridge of high pressure until Tuesday morning, then turn more to the west-northwest then northwest in response to the steering influence of a broad trough of low pressure moving across the Western Atlantic on Tuesday and Wednesday. This should allow Igor to pass several hundred miles to the northeast of the Lesser Antilles. In the longer range, Igor appears likely to be a threat to Bermuda, and that island can expect tropical storm force winds as early as Friday. Igor does have a small chance of making landfall on the U.S. East Coast or Canada. Climatology shows that about 15% of all tropical cyclones that have existed at Igor's current position have gone on to hit the U.S. East Coast; these odds are about 10% for Bermuda and 10% for Canada. The forecast steering pattern for the period 5 - 10 days from now from the ECMWF and GFS models shows a continuation of the pattern we've seen all hurricane season, with regular strong troughs of low pressure moving off the U.S. East Coast. This pattern favors Igor eventually recurving out to sea without hitting the U.S. or Canada. While the trough expected to recurve Igor out to sea is not as sharp as the troughs that recurved Danielle, Earl, and Fiona, it should still be strong enough to keep Igor from hitting the U.S. However, Newfoundland, Canada could see a close pass. An examination of the tracks of the ten major September hurricanes that have passed closest to Igor's current location (Figure 2) reveals that one of these hurricanes went on to hit the Bahamas and Florida as a Category 2 storm, and another hit Newfoundland as a Category 1 storm. The other eight missed land. One wild card may be the intensification of Julia behind Igor. If Julia develops into a hurricane and moves close to Igor, as some of the models are suggesting, the two hurricanes could interact, affecting the track of Igor unpredictable ways. However, it currently appears the Julia will be much weaker than Igor, and will probably have little impact on her big brother's track.


Figure 2. Historical plot of the tracks of the ten major September hurricanes that have passed closest to Igor's current location.

Caribbean disturbance 92L
Tropical disturbance (92L) over the Central Caribbean, centered about 100 miles south of Jamaica, has changed little over the past day. The storm remains a threat to develop into a tropical depression, but time is running out for it to do so. Satellite loops this morning do not show a surface circulation, but 92L does have a moderate area of intense disorganized thunderstorms that are bringing heavy rain to Jamaica this morning. Kingston, Jamaica has picked up 0.67" of rain thus far this morning from 92L.


Figure 3. Morning satellite image of 92L.

Forecast for 92L
Wind shear over 92L is low, 5 - 10 knots, and is expected to remain low to moderate for the next five days. The waters beneath are hot, 29.8°C, and these warm waters extend to great depth. Water vapor satellite loops show a large area of dry air lies to the north and west of 92L, and this dry air has been interfering with development of 92L. NHC is putting the odds of 92L developing into a tropical depression by Wednesday at 40%. Given the current disorganized state of 92L, it would be difficult for it to intensify quickly enough to become any stronger than a tropical storm with 50 mph winds by Wednesday, when it will move over Belize and Mexico's Yucatan Peninsula. Once 92L crosses the Yucatan, the ridge of high pressure steering it is expected to remain in place, forcing 92L to a second landfall in Mexico several hundred miles south of the Texas border. A Hurricane Hunter aircraft is scheduled to investigate 92L this afternoon.

Julia
Tropical Storm Julia formed between the Cape Verdes Islands and coast of Africa yesterday, bringing some heavy rain squalls and gusty winds to the Cape Verdes, but no sustained winds of tropical storm force. Julia is headed northwest, out to sea, and it is unlikely that this storm will trouble any land areas . Shear is low enough over the next few days to allow Julia to become a hurricane, but shear will rise sharply 4 - 5 days from now, limiting the potential for Julia to become a major hurricane.

Elsewhere in the tropics
The NOGAPS model is calling for a new tropical depression to form off the coast of Africa 6 - 7 days from now.

Next post
I'll have a new post Tuesday morning.

Jeff Masters

Hurricane

92L still a threat to develop; Igor a hurricane; TD 12 forming near Africa

By: JeffMasters, 2:18 PM GMT on September 12, 2010

Tropical disturbance (92L) over the Central Caribbean, a few hundred miles south of the Dominican Republic, remains a threat to develop into a tropical depression. Satellite loops this morning show 92L may be starting to form a surface circulation, and an Air Force Hurricane Hunter aircraft will investigate 92L this afternoon to see if a tropical depression is forming.

The storm has only a modest area of heavy thunderstorm with limited low-level spiral banding and upper-level outflow, thanks to an infusion of dry air last night that disrupted the storm. Long range radar out of Puerto Rico shows that heavy rains are affecting that island, but there is no rotation to the radar echoes evident. Wind shear over 92L is low, 5 - 10 knots. The waters beneath are hot, 29.5°C, and these warm waters extend to great depth. Water vapor satellite loops show a large area of dry air lies to the north and west of 92L, and this dry air could interfere with development at times over the next few days.


Figure 1. Morning satellite image of 92L.

Track forecast for 92L
The disturbance is moving west to west-northwest at 15 mph, and steering currents favor a continuation of this motion for the next three days. Model support for development is scattered. The GFS and NOGAPS models do not develop 92L. The GFDL and ECMWF models predict development, with a track taking 92L into Belize or Mexico's Yucatan Peninsula on Wednesday. On this track, the southern Dominican Republic can expect heavy rains of 3 - 6 inches today through Monday morning; southern Haiti can expect similar rains tonight through Monday night, and Jamaica and the Cayman Islands can expect heavier rains of 4 - 8 inches Monday and Tuesday. Eastern Cuba can expect rains in the 2 - 4 inch range. Once 92L crosses the Yucatan, the ridge of high pressure steering it is expected to remain in place, forcing 92L to a second landfall in Mexico south of the Texas border.

Intensity forecast for 92L
NHC is putting the odds of 92L developing into a tropical depression by Tuesday at 50%; I'd put them higher, at 70%. However, time is running out for 92L to become a hurricane before hitting the Yucatan Peninsula on Wednesday. Given the current disorganized state of 92L, it would be difficult for it to intensify quickly enough to become a hurricane by then. The storm may also suffer another of its mysterious evening collapses, where it loses most of its heavy thunderstorm activity. However, the SHIPS model predicts wind shear will remain low, 5 - 10 knots, through the period, and water temperatures are certainly warm enough to support development. The main detriment to intensification is likely to be dry air, and 92L could wrap in some of the dry air to its northwest at times, slowing down development. There are a number of research flights being made into 92L this afternoon that should help long-term efforts to make better predictions in the future on whether or not disturbances like this will develop or not.


Figure 2. Morning satellite image of Igor.

Igor
Hurricane Igor appears destined to become a large and powerful major hurricane over the Central Atlantic in the days to come. Wind shear is low, 5 - 10 knots, and is expected to drop below 5 knots for the next five days. Waters are warm, 28°C, and will warm to 29°C by Wednesday. Igor has moistened its environment enough to keep the dry air of the Saharan Air Layer (SAL) at bay. Igor is undergoing a period of rapid intensification today, and will probably be a Category 3 or 4 hurricane by Monday.

The track forecast for Igor remains unchanged. Igor will move west under the influence of a strong ridge of high pressure for the next 2 - 3 days, then turn more to the west-northwest then northwest in response to the steering influence of a broad trough of low pressure moving across the Western Atlantic on Tuesday and Wednesday. This should allow Igor to pass several hundred miles to the northeast of the Lesser Antilles. In the longer range, Igor may be a threat to Bermuda, and does have a small chance of making landfall on the U.S. East Coast or Canada. Climatology shows that about 15% of all tropical cyclones that have existed at Igor's current position have gone on to hit the U.S. East Coast; these odds are about 10% for Bermuda and 10% for Canada. The forecast steering pattern for the period 5 - 12 days from now from the ECMWF and GFS models shows a continuation of the pattern we've seen all hurricane season, with regular strong troughs of low pressure moving off the U.S. East Coast. This pattern favors Igor eventually recurving out to sea without affecting any land areas. Recent runs of the ECMWF model indicate that these troughs may not be as intense as previously thought, so it is possible Igor has a higher chance than usual to hit land than climatology suggests. One wild card may be the possible development of TD 12 behind Igor. If TD 12 develops into a hurricane, and moves close to Igor, as some of the models are suggesting, the two hurricanes could rotate around a common center, forcing Igor more towards the coast of the U.S. The long term fate of Igor is difficult to predict at this point.

Tropical Depression Twelve forms
Tropical Depression Twelve formed between the Cape Verdes Islands and coast of Africa this morning, and is already affecting the Cape Verdes with winds near tropical storm strength; sustained winds of 35 mph were recorded in the northwest Cape Verdes this morning. You can follow the progress of TD 12 through the Cape Verdes today using our wundermap.

Next post
I'll have a new post Monday morning, and perhaps late this afternoon if events warrant.

Jeff Masters

Hurricane

Potentially dangerous 92L steadily developing; Igor nears hurricane strength

By: JeffMasters, 3:04 PM GMT on September 11, 2010

A tropical disturbance (92L) over the Eastern Caribbean, a few hundred miles south of Puerto Rico, is steadily organizing and appears likely to develop into a tropical depression by tonight or Sunday morning. Satellite loops show an impressive and expanding region of heavy thunderstorms, with good spiral banding and respectable upper-level outflow on all sides. Long range radar out of Puerto Rico shows that heavy rains are now affecting that island, but there is no rotation to the radar echoes evident. However, the rain bands are becoming more intense and more organized. San Juan, Puerto Rico reported a heavy rain squall at 8:44 am this morning, and radar estimates suggest two inches of rain fell in this squall just southeast of San Juan. Wind shear over 92L is low, 5 - 10 knots. The waters beneath are at near-record warmth, 30°C, and these warm waters extend to great depth. Water vapor satellite loops show a large area of dry air lies to the north and west of 92L, and this dry air could interfere with development at times over the next few days.


Figure 1. Morning satellite image of 92L.

Track forecast for 92L
The disturbance is moving west-northwest at 11 mph, and steering currents favor a continuation of this motion for the next three days. Model support for development is scattered. The GFS and NOGAPS models do not develop 92L. The GFDL and ECMWF models predict development, with a track taking 92L into Mexico's Yucatan Peninsula on Wednesday. The HWRF model has a more northwesterly track, taking 92L over the Dominican Republic, Haiti, and Cuba, but this model has been trending too far north in its tracks. I expect 92L will follow a path south of the islands, bringing it near or just south of Jamaica on Monday, then into the Yucatan Peninsula on Wednesday. On this track, the southern Dominican Republic can expect heavy rains of 3 - 6 inches tonight through Monday morning; southern Haiti can expect similar rains Sunday through Monday, and Jamaica and the Cayman Islands can expect heavier rains of 4 - 8 inches Monday and Tuesday. Eastern Cuba will probably escape 92L's heaviest rains in this scenario (Figure 2.)

Intensity forecast for 92L
I can't find any reason to doubt this will be a tropical storm by Sunday or Monday, and potentially a Category 1 or 2 hurricane by Wednesday, if 92L avoids passage over Hispaniola and Cuba. The SHIPS model predicts wind shear will remain low, 5 - 10 knots, through the period, and makes 92L a Category 1 hurricane by Monday night. Water temperatures are certainly warm enough to support development. The main detriment to intensification is likely to be dry air, and 92L could wrap in some of the dry air to its northwest at times, slowing down development. The first Air Force Hurricane Hunter mission into 92L is scheduled for Sunday afternoon, but there will be a research mission by the National Center for Atmospheric Research G-V jet today that will give us valuable information on 92L's large scale environment and potential for development.


Figure 2. Forecast rain amounts from 92L from the 2am EDT Saturday run of the GFDL model. This model predicts most of 92L's heaviest rains will miss Haiti, but will affect Jamaica, the Cayman Islands, and the Yucatan Peninsula. Image credit: Morris Bender, NOAA/GFDL.

Igor
Tropical Storm Igor is very close to hurricane strength, and appears destined to become a large and powerful major hurricane over the Central Atlantic in the days to come. Wind shear is moderate, 15 - 20 knots, waters are warm, 28°C, and Igor has moistened its environment enough to keep the dry air of the Saharan Air Layer (SAL) at bay. Igor will track west under the influence of a strong ridge of high pressure for the next three days, then turn more to the west-northwest in response to the steering influence of a broad trough of low pressure moving across the Western Atlantic on Tuesday and Wednesday. This should allow Igor to pass several hundred miles to the northeast of the Lesser Antilles. In the longer range, Igor may be a threat to Bermuda, and has a slight chance of making landfall on the U.S. East Coast or Canada. Climatology shows that about 10% of all tropical cyclones that have existed at Igor's current position have gone on to hit the U.S. East Coast; these odds are about 10% for Bermuda and 5% for Canada. The forecast steering pattern for the coming two weeks from the GFS model shows a continuation of the pattern we've seen all hurricane season, with regular strong troughs of low pressure moving off the U.S. East Coast. This pattern favors Igor eventually recurving out to sea without affecting any land areas. The odds of Igor hitting land in the U.S. or Canada are probably close to their climatological 10% and 5% probabilities, respectively.

Elsewhere in the tropics
A new tropical wave (Invest 93L) emerged from the coast of Africa yesterday, and is already showing signs of organization. Most of the models predict 93L will develop into a tropical depression 2 - 4 days from now, and NHC is giving 93L a 30% chance of developing by Monday.

Next post
This may be my only post today; I'll have a new post Sunday morning.

Jeff Masters

Hurricane

92L still a threat to develop; record SSTs continue in the tropical Atlantic

By: JeffMasters, 1:44 PM GMT on September 10, 2010

A tropical disturbance (92L) over the Lesser Antilles Islands lost most of its heavy thunderstorms last night, due to an infusion of dry air. However, 92L has redeveloped a moderate amount of heavy thunderstorm activity this morning, and remains a threat to the Caribbean--though not as great a threat as it appeared yesterday. Satellite loops show that 92L's heavy thunderstorms are slowly growing in areal coverage, and are becoming more organized. St. Lucia reported sustained winds of 33 mph this morning in a heavy rain squall, and heavy rain showers and gusty winds can be expected throughout the southern Lesser Antilles Islands today. Martinique radar shows that heavy rains are now affecting that island, but there is no rotation to the radar echoes evident. Surface observations indicate that pressures continue to fall at a number of stations in the Lesser Antilles, but no surface circulation is evident in the wind reports. A strong flow of upper level easterly winds is creating a moderate 10 - 20 knots of wind shear on the south side of 92L. The waters are at near-record warmth, 30°C, and these warm waters extend to great depth. Water vapor satellite loops show a large area of dry air lies over the northern Caribbean, and this dry air could interfere with development over the next few days.

Forecast for 92L
The disturbance is moving westward at 5 mph, but steering currents favor a more west-northwest motion Saturday. Lower shear lies over the Central Caribbean, away from the coast of South America, so any northward component of motion will allow for more significant development. There is drier air to the north, but 92L is steadily moistening the atmosphere in the Caribbean, so dry air may not be a problem for it. Model support for development is less than it was yesterday. The GFS and NOGAPS models do not develop 92L. The HWRF, GFDL, and UKMET models predict development, with a track taking 92L into the Dominican Republic on Sunday as Tropical Storm Julia. These models predict the storm will continue west-northwest, affecting Haiti, Eastern Cuba, Jamaica, and the Southeast Bahamas early next week. The ECMWF model foresees a more southerly track, taking 92L into Mexico's Yucatan Peninsula seven days from now.

Residents of the northern Lesser Antilles Islands and Puerto Rico should anticipate the possibility of heavy rains from 92L affecting their islands on Saturday and Sunday, though most of the action will probably stay south and west. The southern Dominican Republic should see heavy rains of 3 - 6 inches on Sunday and Monday from 92L, and Haiti, Jamaica, and eastern Cuba should anticipate similar rains on Monday and Tuesday. Should 92L make a direct hit on the Dominican Republic, it could destroy the storm, though. NHC is giving 92L a 40% chance of developing into a tropical depression by Sunday, which is a reasonable forecast. The first Air Force Hurricane Hunter mission into 92L is scheduled for Saturday morning, but there will be two research missions into the storm today that will give us valuable information on 92L's large scale environment and potential for development.


Figure 1. Morning satellite image of 92L.

Igor
Tropical Depression Igor has survived a bout with high wind shear, and is now in an environment of moderate 10 - 20 knots of shear that should allow for steady strengthening. Waters are warm, 28°C, and the Saharan Air Layer (SAL) is probably not close enough to Igor to prevent development. The models continue to predict development of Igor into a hurricane 2 - 4 days from now. Igor will track west to west-northwest over the next week, with long range forecasts from the GFS and ECMWF models putting the storm several hundred miles northeast of the Lesser Antilles Islands about 6 - 8 days from now. Climatology shows that about 10% of all tropical cyclones that have existed at Igor's current position have gone on to hit the U.S. East Coast; these odds are about 5% for Canada. The forecast steering pattern for the coming two weeks from the GFS model shows a continuation of the pattern we've seen all hurricane season, with regular strong troughs of low pressure moving off the U.S. East Coast. This pattern favors Igor eventually recurving out to sea without affecting any land areas. The odds of Igor hitting land in the U.S. or Canada are probably close to their climatological 10% and 5% probabilities, respectively.

Elsewhere in the tropics
The GFS and ECMWF models predict the development of a new tropical wave off the coast of Africa 3 - 6 days from now.

August SSTs in the tropical Atlantic set a new record
Sea Surface Temperatures (SSTs) in the Atlantic's Main Development Region for hurricanes had their warmest August on record, according to an analysis I did of historical SST data from the UK Hadley Center. SST data goes back to 1850, though there is much missing data before 1910 and during WWI and WWII. SSTs in the Main Development Region (10°N to 20°N and 20°W to 80°W) were 1.23°C above average during August, beating the previous record of 1.01°C set in August 2005. August 2010 was the 7th straight record warm month in the tropical Atlantic. The five warmest months in history for the tropical Atlantic have all occurred this year; June 2005 comes in sixth place, and August 2010 in seventh. As I explained in detail in a post on record February SSTs in the Atlantic, the Arctic Oscillation (AO) and its close cousin, the North Atlantic Oscillation (NAO), are in large part to blame for the record SSTs, though global warming and Atlantic Multidecadal Oscillation (AMO) also play a role.

The Bermuda-Azores High was weaker than average during August, which drove slower than usual trade winds over the tropical Atlantic. These lower trade wind speeds stirred up less cold waters from the depths than usual, and caused less evaporational cooling than usual, allowing August SSTs to remain at record warm levels. The Bermuda-Azores High and its associated trade winds are forecast to be at near-average strength during the next two weeks, according to the latest run of the GFS model. This means that Atlantic SST anomalies will continue to stay at record warm levels during September, significantly increasing the odds of major hurricanes in the Atlantic.


Figure 2. The departure of sea surface temperature (SST) from average for September 9, 2010. Note the area of cool anomalies off the U.S. East Coast, due to the passage of Hurricane Earl. Cool anomalies are also evident east of Bermuda, due to the passage of Hurricane Danielle. Image credit: NOAA/NESDIS.

Next post
I'll have an update Saturday morning.

Jeff Masters

Hurricane

Flooding, tornadoes for TX, OK; dangerous 92L forms; 4th hottest summer for U.S.

By: JeffMasters, 1:41 PM GMT on September 09, 2010

Dangerous flash flooding is occurring in Eastern Oklahoma this morning, where rainfall rates as heavy as three inches per hour from the remains of Tropical Storm Hermine are occurring. A large area of Eastern Oklahoma received 3 - 6 inches of rain last night and this morning, with radar-estimated rainfall amounts as high as fifteen inches (Figure 2.) Yesterday, Hermine killed two people in Texas, who were attempting to cross flood waters in their vehicles. Hermine dropped 6 - 8 inches of rain in the Dallas/Fort Worth area, creating moderate to major flooding along the Trinity River in Dallas. Two tornadoes touched down near Dallas, and NOAA's Storm Prediction Center logged a total of eight tornado reports in Oklahoma and Texas from Hermine. The latest rainfall totals from NOAA's Hydrometeorological Prediction Center show 15.62" fell in Georgetown, Texas, with fifteen locations in Texas receiving over ten inches of rain. Big city rainfall totals included 7.57" at Austin, 6.73" at San Antonio, 6.52" at Dallas, and 7.20" at Fort Worth.


Figure 1. Radar estimated rainfall for the Dallas/Fort Worth, Texas area from Hermine shows a large area of 6+ inches of rain, with maximum amounts of ten inches.

Figure 2. Radar estimated rainfall for eastern Oklahoma, where up to fifteen inches of rain fell last night and this morning.

Potentially dangerous Lesser Antilles tropical disturbance 92L forms
A tropical disturbance (92L) has developed over the extreme southeastern Caribbean just north of the coast of South America, over the southernmost Lesser Antilles Islands. Surface observations indicate that pressures have been slowly falling at a number of stations, and satellite loops show a modest region of heavy thunderstorm activity is building. A strong flow of upper level easterly winds is creating a moderate 10 - 20 knots of wind shear, and the waters are plenty warm for development. Water vapor satellite loops show a large area of dry air lies over the northern Caribbean, but this dry air should not interfere with development over the next two days.

The disturbance is slowly drifting westward, but steering currents favor a more northwest motion Friday and Saturday. Lower shear lies over the Central Caribbean, away from the coast of South America, so any northward component of motion will allow for more significant development. There is drier air to the north, but 92L is steadily moistening the atmosphere in the Caribbean, so dry air may not be a problem for it. There is substantial model support for development. The disturbance is in a dangerous location for development, and gives me the greatest concern of any Atlantic disturbance so far this year. The models predict that by Saturday, 92L will bring heavy rains to Puerto Rico. These rains will then spread to the Dominican Republic on Sunday, and Haiti, Jamaica, and eastern Cuba on Monday. The longer range track of 92L is uncertain, and will strongly depend on where the storm drifts during the next two days. The ECMWF and GFS models predict a more southerly path through the Western Caribbean towards Belize and Mexico's Yucatan Peninsula, and the NOGAPS and Canadian models predict a more northerly path along the length of Cuba towards Florida. NHC is giving 92L a 40% chance of developing into a tropical depression by Saturday. Stay tuned.


Figure 3. Morning satellite image of the potentially dangerous disturbance in the Southeast Caribbean.

Igor
Tropical Storm Igor is barely hanging on in the face of 20 - 25 knots of winds shear, courtesy of strong upper-level winds out of the east. The shear has exposed Igor's low level circulation to view, and the storm has just one small spot of heavy thunderstorms near its center. Once Igor gets another 200 miles away from Africa, the shear should decline to the moderate range, 10 - 20 knots, and allow steady strengthening to occur. Waters are warm, 28°C, and the Saharan Air Layer (SAL) is well north of Igor, so the storm should intensity once the shear drops. The models are pretty unanimous about developing Igor into a hurricane 3 - 5 days from now. Igor will track west to west-northwest over the next week, with long range forecasts from the GFS and ECMWF models putting the storm several hundred miles northeast of the Lesser Antilles Islands a week from now. Climatology shows that about 20% of all tropical cyclones that have existed at Igor's current position have gone on to hit the U.S. East Coast; these odds are 10% for the U.S. Gulf Coast, 5% for Puerto Rico, and 10% for Canada. The forecast steering pattern for the coming two weeks from the GFS model shows a continuation of the pattern we've seen all hurricane season, with regular strong troughs of low pressure moving off the U.S. East Coast. This pattern favors Igor eventually recurving out to sea without affecting any land areas, and the odds of Igor hitting land are lower than climatology.

Elsewhere in the tropics
The GFS, NOGAPS, and ECMWF models predict the development of a new tropical wave off the coast of Africa 4 - 6 days from now.

Hottest summer in history for 50 million Americans
The U.S. had its fourth warmest summer since record keeping began 116 years ago, according to statistics issued yesterday by the National Climatic Data Center. Only 1936, 2006 and 1934 were hotter. Ten states had their warmest summer on record--Rhode Island, New Jersey, Delaware, Maryland, Virginia, North Carolina, Tennessee, South Carolina, Georgia and Alabama. Seventeen other states had a top-ten warmest summer, including five states that had their second warmest summer in history (Figure 4.) No states had a top-ten coldest summer. Record daily highs outpaced record daily lows by about 4 to 1 during the summer, with 5,287 daily record highs set, and 1,426 record lows. The summer warmth was a pretty remarkable swing from this past winter, which was the 18th coldest in U.S. history.


Figure 4. State-by-state temperature rankings for the summer of 2010. Image credit: National Climatic Data Center.

According to Chris Burt, author of Extreme Weather, approximately 50 - 60 million Americans experienced their hottest summer ever. No summer in U.S. history has affected so many Americans as "hottest-summer-on-record". The following large cities all posted a record hottest summer:

Washington D.C. National Airport: 81.3° (old record 80.0° summer of 1943)
Dulles Airport, VA: 77.8° (old record 76.8° summer of 2007)
Richmond, VA: 81.3° (old record 80.0° summer of 1994)
Atlantic City, NJ: 77.5° (old record 75.8° summer of 2005)
Philadelphia, PA: 79.6° (old record 78.9° summer of 1995)
New York City (Central Park): 77.8° (old record 77.3° summer of 1966)
Trenton, NJ: 77.7° (old record 76.5° summer of 1898)
Wilmington, DE: 77.8° (old record 77.7° summer of 1900)
Baltimore, MD: 79.2° (old record 79.1° summer of 1943)
Norfolk, VA: 81.1° (old record 80.0° summer of 1994)
Tampa, FL: 84.5° (previous record 84.2° in 1998)
Lakeland, FL: 84.6° (previous record 84.4° in 1987)
St. Petersburg, FL: 85.6° (old record 84.6° in 1987)

Santa Barbara, CA was the only major U.S. city that had its coldest summer on record, though several other California cities were unusually cool. San Diego had its 3rd coolest summer, and the Los Angeles airport had its 2nd coolest summer.

Fortunately, it was a very wet summer, and the record heat did not lead to widespread drought. Summer 2010 ranked as the 16th wettest summer in the 116-year record for the contiguous U.S. Wisconsin had its wettest summer on record, and six other states had a top-ten wettest summer. No state had a top-ten driest summer.

Next post
I'll have an update Friday morning.

Jeff Masters

Flood Climate Summaries Hurricane

Major flooding in Austin from Hermine

By: JeffMasters, 1:24 PM GMT on September 08, 2010

Major flooding is occurring in the Austin, Texas region after Tropical Storm Hermine dumped an estimated 10 - 15 inches of rain over the past 24 hours. The flash flood warning for Austin from the National Weather Service at 4am this morning summarized the danger:

"Areas along I-35 and the Balcones Escarpment in and around the Austin Metro area will continue to experience a very dangerous flash flood event over the next few hours. Numerous evacuations and high water rescues have already been reported by the media and law enforcement personnel."

As wunderground's Dr. Rob Carver reports in his blog this morning, hardest hit was the area ten miles north-northwest of Austin, where an NWS cooperative station measured 10.11" of rain yesterday. The rains have swollen the South Fork of the San Gabriel River at Georgetown, Texas to 50-year flood heights.

Hermine has dissipated, but its heavy rains live on, and are now affecting the Dallas/Fort Worth region, where 1 - 3 inch rainfall amounts have been common. Hermine's rains are still lingering over the hard-hit Austin area, but should remain under one inch for the remainder of the morning. However, this afternoon, additional significant rains are possible near Austin as the sun's heat drives thunderstorm development in the very moist airmass over Central Texas.


Figure 1. Radar estimated rainfall for the Austin, Texas area shows that over fifteen inches of rain may have fallen in the region ten miles north-northwest of the city.

Gaston's remains no longer a threat
Dry air has significantly disrupted the remains of Tropical Storm Gaston, which are now over the Dominican Republic. NHC is now giving Gaston a 0% chance of developing, and no models are calling for development. It appears Gaston is finally dead.

Invest 91 off the coast of Africa
A large, well-organized tropical wave (91L) is just off the coast of Africa, near the Cape Verdes Islands, and is bringing sustained winds of 30 mph this morning to Praia in the southeast Cape Verdes. 91L is under a high 20 - 30 knots of wind shear, but this shear will decline to the moderate range, 10 - 20 knots, by Thursday. Water temperatures are warm, 28°C, and 91L has plenty of spin. The Saharan Air Layer (SAL) is well north of 91L, and should not be an impediment to development over the next few days. The models are pretty unanimous about developing 91L into Tropical Storm Igor sometime in the next 1 - 3 days. NHC is giving 91L a 70% chance of developing into a tropical depression by Friday. The GFDL model predicts 91L will be Hurricane Igor five days from now. The storm will track west to west-northwest over the next week, with long range forecasts from the GFS and ECMWF models putting 91L several hundred miles northeast of the Lesser Antilles Islands 7 - 10 days from now. History shows that about 20% of all tropical cyclones that have existed at 91L's current position have gone on to hit the U.S. East Coast; these odds are 10% for the U.S. Gulf Coast, 5% for Puerto Rico, and 10% for Canada. The forecast steering pattern for the coming two weeks from the GFS model shows a continuation of the pattern we've seen all hurricane season, with regular strong troughs of low pressure moving off the U.S. East Coast. This pattern favors a continuation of the sort of tracks we saw for Danielle, Earl, and Fiona, with threats to the northern Lesser Antilles, Bermuda, the U.S. East Coast, and Canada.


Figure 2. Morning satellite image of Invest 91L (Igor?)

Elsewhere in the tropics
The GFS and ECMWF models are predicting the development of a new tropical wave off the coast of Africa 5 - 6 days from now.

Death toll in Guatemala from Tropical Depression 11E rises to 54
In the Eastern Pacific, heavy rains from Tropical Depression 11E have killed at least 54 people in Guatemala, with many more missing and feared dead. The heavy rains triggered nearly 200 landslides and collapses, causing damages near $500 million. Fifteen landslides hit portions of the Inter-American Highway, burying a number of vehicles and a bus. Tropical Depression 11E formed on September 3, moved over Mexico and Guatemala, and dissipated by the next day. Remnants from the depression may have played a role in the formation of Tropical Storm Hermine in the Gulf of Mexico on September 5.

Guatemala is still recovering from the impacts of Tropical Storm Agatha, which killed 287 people in the country and did over $1 billion in damage in May. This September's heavy rains in Guatemala come on the heels of the rainiest August in Guatemala's history, according to preliminary data from the National Institute of Seismology, Volcanology, Meteorology and Hydrology (INSIVUMEH). Rain was more than 100% above average in many parts of the country, and more than 200% above average in some regions. September and October are historically Guatemala's rainiest months, and any additional tropical cyclones which affect the country can be expected to cause more serious flooding.


Figure 3. Satellite image from Friday, September 3, 2010, showing Tropical Depression 11E over Mexico and Guatemala. Image credit: NASA.

Next post
I'll have an update Thursday morning.

Jeff Masters

Hurricane

Hermine drenching Texas; Gaston's remains less organized

By: JeffMasters, 1:21 PM GMT on September 07, 2010

Tropical Storm Hermine hit the Mexican coast 40 miles south of the Texas border at 9:30 pm EDT last night, with 60 mph sustained winds. Top winds observed in Texas from the storm were 50 mph with gusts to 59 mph at Port Isabel near the Mexican border, and winds at Brownsville hit 45 mph, gusting to 69 mph. Harlingen had the highest gust observed from Hermine, 72 mph, and local storm reports indicate that half of the city lost power and a roof caved in on an apartment complex, with no injuries. Heavy rains have fallen along a 30-mile wide stretch of the Mexican and Texas coast, with 1.41" reported thus far in Harlingen, 3.71" at Brownsville, and 2.00" at Corpus Christi. Radar estimated rainfall amounts (Figure 3) exceed four inches along most of the Lower Texas coast, with maximum amounts near eleven inches twenty miles north of Brownsville.


Figure 1. Radar image of Hermine at landfall.


Figure 2. MODIS satellite image of Hermine at 12:45pm EDT Monday September 6, 2010. Image credit: NASA.

Hermine became a tropical depression at 11pm Sunday night, and intensified into a 65 mph tropical storm in just 21 hours, an extremely fast intensification rate. It turns out that the southwestern Gulf of Mexico's Bay of Campeche, where Hermine formed, is prone to these sort of rapidly intensifying tropical storms. This region produced two similar rapidly intensifying storms in 2007, Humberto and Lorenzo. Since 6-hourly position records of Atlantic hurricanes began in 1970, Hurricane Humberto holds the 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). The curvature and topography of the land surrounding the Bay of Campeche help induce a counter-clockwise spin to the air over the region, which helps get tropical storms spinning up unusually quickly. Helping the spin-up process yesterday for Hermine were the very warm 30°C waters, low 5 - 10 knots of wind shear, and moist atmosphere.


Figure 3. Morning radar-estimated rainfall for Hermine.

Forecast for Hermine
Heavy rain and isolated tornadoes will continue across southern and central Texas today and tomorrow. Hermine is expected to accelerate northward today, limiting the potential for damaging floods along its future path. The storm's rains will help alleviate moderate to severe drought conditions affecting Central Texas.

Gaston's remains less organized
Dry air has significantly disrupted the remains of Tropical Storm Gaston, which are now over the northern Lesser Antilles Islands and Puerto Rico. Morning visible satellite imagery shows that Gaston's remains no longer have a well-defined surface circulation, though there is still some spin. Latest radar out of Martinique and Puerto Rico show a few heavy rain showers moving through the islands, but no organization to the showers. A large amount of dry air surrounds Gaston's remains on all sides, as seen on water vapor satellite loops. None of the computer models show Gaston redeveloping, and NHC has downgraded the odds of development to 10%. I think the odds should be higher than this, perhaps 30%. Gaston's remains will be disrupted some on Wednesday, when they will encounter the high terrain of Hispaniola.

Elsewhere in the tropics
There are two tropical waves off the coast of Africa that NHC is giving a 10% chances of developing into tropical depressions by Thursday. The models are fairly unanimous in predicting development of one or more tropical waves off the coast of Africa 3 - 7 days from now. The next storm will be called Igor.

Eastern Pacific Tropical Depression 11E kills 44 in Guatemala
In the Eastern Pacific, heavy rains from Tropical Depression 11E killed at least 44 people in Guatemala over the weekend. At least 56 are injured, and 16 missing. The heavy rains triggered fifteen landslides that hit portions of the Inter-American Highway, burying a number of vehicles and a bus. Guatemala is still recovering from the impacts of Tropical Storm Agatha, which killed 287 people in the country and did over $1 billion in damage.


Figure 4. Satellite image from Friday, September 3, 2010, showing Tropical Depression 11E over Guatemala. Image credit: NASA.

"Hurricane Haven" airing again this afternoon
Tune into another airing of my live Internet radio show, "Hurricane Haven", at 4pm EDT today. Listeners will be able to call in and ask questions. The call in number is 415-983-2634, or you can post a question to broadcast@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line.

Today's show will be about 30 minutes, and you can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml. The show will be recorded and stored as a podcast.

Next post
I'll have an update Wednesday morning.

Jeff Masters

Hurricane

Intensifying Hermine closes in on the Texas/Mexico coast

By: JeffMasters, 9:47 PM GMT on September 06, 2010

Steadily intensifying Tropical Storm Hermine is closing in on the coast near the Texas/Mexico border, and should move ashore late tonight. Hermine became a tropical depression at 11pm last night, and could become a minimal hurricane by 11 pm tonight. Hermine's rate of intensification from nothing to a strong tropical storm is one of the fastest on record. It turns out that the extreme southwestern Gulf of Mexico's Bay of Campeche, where Hermine formed, is prone to these sort of rapidly intensifying tropical storms. The curvature and topography of the land help induce a counter-clockwise spin to the air over the region, which helps get tropical storms spinning up unusually quickly. Helping the spin-up process are the very warm 30°C waters, low 5 - 10 knots of wind shear, and moist atmosphere. Hermine promises to be a very wet storm, and latest long range radar out of Brownsville, Texas shows a large area of heavy rain has been drenching southern Texas and northern Mexico all afternoon, with radar estimated rainfall amounts exceeding two inches in a few areas along the coast. Radar loops show that an eyewall is attempting to form, but a region of dry air from over land spiraled into Hermine's core between 4 - 5pm EDT, disrupting eyewall formation. However, it now appears that Hermine has closed off its eye from this dry air, which should aid in intensification. Satellite imagery shows Hermine has vigorous thunderstorms with very cold tops, and improving low-level spiral banding.

Forecast for Hermine
Hermine doesn't have much time over water before it comes ashore, which is a good thing. The storm is steadily organizing, and has a shot at reaching hurricane strength before the center moves ashore late tonight, near midnight. Heavy rain will be the main threat from Hermine, though isolated tornadoes may also cause damage, particularly over South Texas. Hermine is expected to accelerate through Central Texas Tuesday and Wednesday, and the storm's rains will help alleviate moderate to severe drought conditions affecting Central Texas.


Figure 1. Late afternoon radar image of Tropical Storm Hermine. Note the band of dry air spiraling into the core of the storm from the north.

Gaston continues to suffer from dry air
An Air Force Hurricane Hunter aircraft spent the afternoon in Gaston's remains, and found a weak 1012 mb center of low pressure with only a limited region of westerly winds on the south side of the center of circulation. Top surface winds uncontaminated by heavy rain seen by their SFMR instrument were in the 30 - 35 mph range. The airplane found plenty of dry air in the storm's environment, and there are not enough heavy thunderstorms in ex-Gaston's circulation for it to qualify as a tropical depression. The remains of Gaston are now approaching the northern Lesser Antilles, and residents can expect a few heavy rain showers and wind gusts up to 40 mph beginning early this evening and continuing into the night. Latest radar out of Martinique doesn't show much in the way of heavy rain, and satellite imagery confirms that the thunderstorm activity associated with Gaston's remains is quite sparse. A large amount of dry air surrounds Gaston's remains on all sides, as seen on water vapor satellite loops.


Figure 2. Afternoon satellite image of the remains of Gaston, approaching the Lesser Antilles Islands.

Forecast for Gaston
There is little change to the forecast for Gaston's remains. Dry air will continue to be the major impediment to development, and the system is unlikely to become a tropical depression today. However, wind shear, which is currently a moderate 10 knots, is forecast by the latest SHIPS model run to fall very low, 0 - 5 knots, tonight through Wednesday. With almost no wind shear affecting it, Gaston will a better chance of keeping the moisture from its heavy thunderstorms near its core on Tuesday. This will insulate the storm from the dry air surrounding it. The atmosphere is also moister in the eastern Caribbean, further increasing the chances of development. I believe it is probable Gaston will become a tropical depression again on Tuesday. NHC is currently giving Gaston a 70% chance of developing into a tropical depression by Wednesday, which is a reasonable forecast.

Heavy rain showers and gusty winds from the storm will affect Puerto Rico Tuesday morning through Wednesday afternoon. This activity will spread to the Dominican Republic Tuesday afternoon through Thursday morning. Assuming dry air and an encounter with Hispaniola's high mountains do not destroy Gaston, heavy rain from the storm should move over Haiti, eastern Cuba, and Jamaica Wednesday night and Thursday morning. The models don't give much support for Gaston surviving past Wednesday. The ECMWF, GFS, NOGAPS, Canadian, and HWRF models all dissipate Gaston. However, two models--the GFDL and UKMET--predict that Gaston will survive the dry air and an encounter with Hispaniola, and pass far enough south of the island to find a favorable environment in the Central Caribbean for development on Wednesday. Wind shear will be low, water temperatures will be hot, and the atmosphere will be plenty moist. Gaston could intensify into a hurricane in the Western Caribbean by the end of the week, as predicted by the latest run of the GFDL model.

Elsewhere in the tropics
The models are fairly unanimous in predicting development late this week of a tropical wave expected to emerge from the coast of Africa on Tuesday or Wednesday. The next storm will be called Igor.

Next post
I'll have an update in the morning.

Jeff Masters

Hurricane

Hurricane watches for Mexico and Texas as Hermine suddenly develops

By: JeffMasters, 4:15 PM GMT on September 06, 2010

Hurricane watches are up for the Texas/Mexico border region as fast developing Tropical Storm Hermine steams towards the coast at 13 mph. Hermine was a tropical depression twelve hours ago, got its name just six hours ago, but already is a threat to intensify into a hurricane by tonight. It's remarkable how fast Gulf of Mexico disturbances can blow up into strong tropical storms, when the right mix of warm waters and low wind shear develops. Indeed, water temperatures are a very warm 30°C, wind shear is a low 5 - 10 knots, and the atmosphere is very moist in the Gulf--ideal conditions for a tropical storm. Hermine promises to be a very wet storm, and latest long range radar out of Brownsville, Texas shows a large area of heavy rain has moved ashore over southern Texas and northern Mexico, with radar estimated rainfall amounts already exceeding two inches in a few areas along the coast. Radar loops show that an eyewall may be beginning to form, and I expect this process will continue through the afternoon and early evening. Satellite imagery shows that Hermine is getting more organized, with vigorous thunderstorms with very cold tops building, low-level spiral bands developing, and improving upper-level outflow occurring on all sides except the west. There is some dry air to the west of Hermine over land that is restricting the storm's development there.

Forecast for Hermine
Hermine doesn't have much time over water before it comes ashore, which is a good thing. Hermine is organizing rapidly, and has a shot at reaching hurricane strength before the center moves ashore late tonight, near midnight. Neither the GFDL or HWRF models develop Hermine into a hurricane, but the HWRF model does predict that tropical storm force winds of 39+ mph will affect the coast as far north as Corpus Christi, Texas. Heavy rain will be the main threat from Hermine, though isolated tornadoes may also cause damage, particularly over South Texas. Hermine is expected to accelerate through Central Texas Tuesday and Wednesday, and the storm's rains will help alleviate moderate to severe drought conditions affecting Central Texas.


Figure 1. Early afternoon radar image of Tropical Storm Hermine.

Gaston continues to suffer from dry air
The remains of Tropical Storm Gaston are now approaching the northern Lesser Antilles, and residents can expect a few heavy rain showers and wind gusts up to 40 mph beginning late this afternoon and continuing into the night. A pass from the ASCAT satellite this morning at 9:03 am EDT showed a large region of 25 mph winds on the north side of Gaston's circulation, and these winds will move into the northern Lesser Antilles late this afternoon. Latest radar out of Martinique doesn't show much in the way of heavy rain, and satellite imagery confirms that the thunderstorm activity associated with Gaston's remains is quite sparse. Gaston does have developed a well-organized surface circulation, but not enough heavy thunderstorm activity to be considered a tropical depression. A large amount of dry air surrounds Gaston's remains on all sides, as seen on water vapor satellite loops.


Figure 2. Morning satellite image of the remains of Gaston, approaching the Lesser Antilles Islands.

Forecast for Gaston
Dry air will continue to be the major impediment to development for Gaston, and the system is unlikely to become a tropical depression today. However, wind shear, which is currently a moderate 10 knots, is forecast by the latest SHIPS model run to fall very low, 0 - 5 knots, tonight through Wednesday. With almost no wind shear affecting it, Gaston will a better chance of keeping the moisture from its heavy thunderstorms near it core on Tuesday. This will insulate the storm from the dry air surrounding it. The atmosphere is also moister in the eastern Caribbean, further increasing the chances of development. I believe it is probable Gaston will become a tropical depression again on Tuesday. NHC is currently giving Gaston a 70% chance of developing into a tropical depression by Wednesday, which is a reasonable forecast. The models don't give much support for Gaston surviving past Wednesday, since many of them have the storm hitting the rugged island of Hispaniola, disrupting the storm.

Heavy rain showers and gusty winds from the storm will affect Puerto Rico Tuesday morning through Wednesday afternoon. This activity will spread to the Dominican Republic Tuesday afternoon through Thursday morning. Assuming dry air and an encounter with Hispaniola's high mountains do not destroy Gaston, heavy rain from the storm should move over Haiti, eastern Cuba, the Turks and Caicos Islands, and Jamaica Wednesday night and Thursday morning. Though none of the global dynamical computer models are showing this, should Gaston survive the dry air and its coming encounter with Hispaniola, the storm will find itself in a very favorable environment for development in the Western Caribbean late in the week, and could intensify into a hurricane by next weekend.

Elsewhere in the tropics
The models are fairly unanimous in predicting development late this week of a tropical wave expected to emerge from the coast of Africa on Tuesday or Wednesday. The next storm will be called Igor, and let's hope it doesn't live up to its fearsome-sounding name!

Next post
There will be an update by early this evening.

Jeff Masters

Hurricane

Gaston still a threat to redevelop

By: JeffMasters, 3:17 PM GMT on September 05, 2010

For the first time since August 22, when Danielle became a tropical storm, there are no named storms active in the Atlantic. An extratropical storm absorbed Tropical Storm Earl last night, bringing an end to the 11-day life of the 2010 season's longest-lived storm. While Earl was mostly a non-event for North Carolina and New England, the storm gave Nova Scotia a solid pounding, reminding us of what could have easily happened to New England had the forecast track deviated slightly to the left. Kudos go to the computer models and NHC, who successfully predicted the path of Earl very accurately four days in advance. As we approach the climatological peak of Atlantic hurricane season, which occurs on September 10, there are no indications that today's break in the action represents a beginning of an extended quiet period in the Atlantic. Indeed, we have two systems that could become tropical depressions in the next day, and we also have model predictions of another storm to come late in the week.


Figure 1. Morning satellite image of the remains of Gaston, approaching the Lesser Antilles Islands.

Gaston near tropical depression status again
The remains of Tropical Storm Gaston, located about 700 miles east of the Lesser Antilles Islands and moving west at about 13 mph, are close to reaching tropical depression status again. Recent satellite imagery shows that Gaston's remains have developed a well-organized surface circulation, but not enough heavy thunderstorm activity to be considered a tropical depression. A large amount of dry air surrounds Gaston's remains on all sides, as seen on water vapor satellite loops. This dry air will continue to be a major impediment to development. The latest SHIPS model forecast predicts shear will remain moderate, 10 - 15 knots, for the next three days, then fall to the low range. The winds creating the shear are coming from the east, where a tongue of dry air has intruded. These easterly winds will be able to drive the dry air into Gaston's core, disrupting it, unless the storm can find a moister environment, or moisten its environment on its own by generating enough heavy thunderstorms. Gaston has managed to develop more heavy thunderstorms near its center of circulation late this morning, but the amount of dry air it is battling is formidable. Even if Gaston does manage to become a tropical depression today, development will be slow over the next few days, due to the dry air. When Gaston passes over or just to the northeast of the Lesser Antilles Islands early Tuesday morning, the storm is unlikely to have more than 50 mph winds. More significant development is possible later in the week, as the atmosphere should be moister for Gaston. Gaston may threaten Puerto Rico on Wednesday, the Dominican Republic on Thursday, and Haiti, Jamaica, and/or the Turks and Caicos Islands by Friday, depending upon the storm's interaction with a trough of low pressure expected to move off the U.S. East Coast later this week. The earlier Gaston develops into a tropical storm, the more likely it is to "feel" the upper-level winds of the approaching trough, and curve more to the northwest. The HWRF model predicts Gaston will develop by Monday, and pass just northeast of the Lesser Antilles Islands Tuesday morning. The GFDL model, on the other hand, delays development until Wednesday, keeping Gaston in the Caribbean. The GFDL has Gaston hitting Jamaica as a strong tropical storm on Friday morning. However, the GFDL forecast is dubious, because on Wednesday and Thursday, Gaston may have an encounter with the high mountains of the island shared by the Dominican Republic and Haiti, Hispaniola, which could easily destroy a system as fragile as Gaston. Gaston has a 70% chance of developing into a tropical depression by Tuesday, according to NHC.

Gulf of Mexico disturbance 90L
A concentrated area of heavy thunderstorms (90L) has developed over the extreme southwestern Gulf of Mexico, in the Bay of Campeche. Satellite imagery shows that this disturbance is disorganized, but has some modest spin to it. The disturbance is under a moderate 10 - 15 knots of wind shear, and has a 60% chance of developing into a tropical depression by Tuesday, according to NHC. The disturbance is headed northwest at 5 - 10 mph, and should bring heavy rains to the Texas/Mexico border region on Monday, according to the latest run of the GFS model. The main impediment to development will be the limited time 90L has over water; the storm will be ashore by Tuesday, which doesn't give it much time to develop.

Elsewhere in the tropics
The GFS and NOGAPS models are predicting development on Thursday of a tropical wave that will emerge from the coast of Africa on Tuesday or Wednesday.

Next post
I'll have an update Monday morning.

Jeff Masters

Hurricane

Earl hits Nova Scotia but spares New England; Gaston still a threat

By: JeffMasters, 4:30 PM GMT on September 04, 2010

Tropical Storm Earl roared ashore over western Nova Scotia late this morning, bringing heavy rain and tropical storm force winds to much of the province. The capital of Halifax recorded sustained winds of 51 mph, gusting to 75 mph at 12:48pm AST this afternoon, and the power is out to tens of thousands of residents in Nova Scotia. Winds were stronger at McNabs Island, in Halifax Harbor, where sustained winds of 64 mph, gusting to 76 mph, occurred at noon AST.

Earl's center passed about 100 miles southeast of Nantucket, Massachusetts, at 1am EDT this morning, and the winds on the weak left side of the storm never reached sustained tropical storm strength (39 mph) at any New England land station. The peak wind gust in Massachusetts may have been the 58 mph gust recorded on Cape Cod 5 miles south-southeast of Barnstable early this morning. Earl did bring some very high waves to New England; waves at the buoy 60 miles southeast of Nantucket peaked at 27 feet early this morning. Heavy rain from Earl--over five inches in some locations--caused localized flooding and road closures on Cape Cod and on Marthas Vineyard.


Figure 1. Hurricane Earl as seen from the International Space Station on Thursday, September 2, 2010. Image credit: NASA astronaut Douglas Wheelock.


Figure 2. Radar estimated rainfall from Earl from the Cape Cod radar.

Gaston a threat to develop
Recent satellite imagery shows that Gaston's remains have developed a well-organized surface circulation, but not enough heavy thunderstorm activity to be considered a tropical depression. A large amount of dry air surrounds Gaston's remains on all sides, as seen on water vapor satellite loops. This dry air will continue to be a major impediment to development. The latest SHIPS model forecast predicts shear will remain moderate, 10 - 15 knots, for the next four days, then fall to the low range. The winds creating the shear are coming from the east, where a tongue of dry air has intruded. These easterly winds will be able to drive the dry air into Gaston's core, disrupting it, unless the storm can find a moister environment. It is also possible that Gaston may be able to protect its core by wrapping moisture around to its east side; recent visible satellite imagery shows a band of moisture wrapping around along Gaston's south side. If this process is successful, Gaston may have a good chance of becoming a tropical depression on Sunday. I suspect there is too much dry air in Gaston's environment for Gaston to develop into a tropical depression today. The atmosphere is moister near the Lesser Antilles Islands, and Gaston has a better chance of developing on Monday when it finds this moister environment. NHC is giving Gaston a 70% chance of regenerating into a tropical depression by Monday. The models are in fairly good agreement bringing Gaston though the central or northern Lesser Antilles Islands on Tuesday. The storm should then slow down and head more to the west-northwest on Wednesday and Thursday, in response to a large trough of low pressure expected to move off the U.S. East Coast. Puerto Rico and the Dominican Republic might be at risk of a strike by a reborn Tropical Storm Gaston by Thursday, if the storm follows a more southerly track over the next few days.


Figure 3. Morning satellite image of Gaston's remains.

Gulf of Mexico disturbance
A concentrated area of heavy thunderstorms has developed over the extreme southwestern Gulf of Mexico, in the Bay of Campeche. This disturbance is under a low 5 - 10 knots of wind shear, and has a 20% chance of developing into a tropical depression by Monday, according to NHC. The disturbance is headed northwest at 5 - 10 mph, but could turn more to the north-northwest and bring heavy rains to the Texas/Mexico border region on Monday, according to the latest run of the GFS model.

99L
A tropical wave (99L) near the Cape Verdes Islands off the coast of Africa is moving northwestward at about 10 mph. The wave has a bit of spin to it, but not much heavy thunderstorm activity. This system is under moderate wind shear, but is headed towards a region of high wind shear northwest of the Cape Verdes Islands. This shear will very likely destroy the disturbance by Tuesday. NHC is giving 99L a 20% chance of developing into a tropical depression by Monday afternoon.

Elsewhere in the tropics
The GFS and ECMWF models are predicting development 3 - 6 days from now of a tropical wave that hasn't emerged from the coast of Africa yet.

Next post
I'll have an update by 1pm Sunday afternoon.

Jeff Masters

Hurricane

Earl's rain bands move over New England; Gaston regenerating?

By: JeffMasters, 9:09 PM GMT on September 03, 2010

Hurricane Earl has remained roughly constant in intensity over the past six hours, as it heads north-northeast at 20 mph towards New England. The latest center fix from the Hurricane Hunters, at 1:14pm EDT, found the pressure had remained constant since late morning, at 961 mb. Long range radar out of Long Island shows that Earl's outermost spiral bands have already brought as much as one inch of rain to portions of Massachusetts and Rhode Island, with lesser amounts on Long Island and in Connecticut.


Figure 1. Afternoon radar image from the Long Island, New York radar.

Forecast for Earl
The latest set of model runs from 8am EDT (12Z) this morning show little change to Earl's track. Earl is still expected to pass 20 - 50 miles southeast of Nantucket and Cape Cod, Massachusetts, at about 2am Saturday. The latest SHIPS model forecast of wind shear continues to show that shear will increase to the high range, 20 - 30 knots, on Saturday. Ocean temperatures will plunge to 20°C early Saturday morning, resulting in considerable weakening. Earl will probably be a strong tropical storm with 70 mph winds early Saturday morning, when it will make its closest approach to New England, and have 65 mph winds on Saturday afternoon, when it is expected to make landfall in Nova Scotia or New Brunswick, Canada. I have no substantive changes to make to the impacts likely for New England and Canada that I discussed in this morning's post.


Figure 2. Wind field analysis of Hurricane Earl from 3:30pm EDT Friday, September 3, 2010. Note the 15 mph (13 kt) asymmetry in Earl's wind field, caused by the storm's forward motion of 20 mph to the north-northeast at the time. The highest contour had top winds of 65 kt (75 mph) surrounding the "+" on the east side of Earl--the strong right front quadrant of the storm. However, winds on the left (northwest) side were just 52 knots (60 mph.) The asymmetry was greater--about 20 mph--at 6:30 am EDT this morning. Image credit: NOAA/AOML/Hurricane Research Division.

Fiona
Tropical Storm Fiona has changed little this afternoon. Satellite loops continue to show that Fiona is a naked swirl of low clouds with just one diminishing spot of heavy thunderstorms on the southwest side of the circulation. High wind shear from Earl should continue to affect Fiona over the next two days, and will probably destroy the storm on Saturday.


Figure 3. Afternoon satellite image of Gaston's remains.

Gaston may be regenerating
Recent satellite imagery continues to show that Gaston's remains are re-organizing. Gaston has a broad surface circulation, but not enough heavy thunderstorm activity to be considered a tropical depression. A large amount of dry air lies to the west and north of Gaston's remains, as seen on water vapor satellite loops. This dry air will continue to be a major impediment to development. The latest SHIPS model forecast predicts shear will remain moderate, 10 - 15 knots, for the next five days. The winds creating the shear are coming from the east, where the atmosphere is relatively moist, so this shear will be less harmful than usual for development. NHC is giving Gaston a 50% chance of regenerating into a tropical depression by Sunday; I put these odds higher, at 60%. The GFS, UKMET, and GFDL models develop Gaston and predict it will move though the Lesser Antilles on Wednesday. The NOGAPS and HWRF models also develop Gaston, but predict a slower motion, bringing the storm near the northern Lesser Antilles 6 - 7 days from now. Given the steady increase in organization of Gaston's remains today and high degree of model support for regeneration, I expect Gaston will be a tropical storm again, early next week.

99L
A tropical wave (99L) between the coast of Africa and the Cape Verdes Islands, is moving northwestward at about 10 mph. The wave has a bit of spin to it, and a modest amount of heavy thunderstorms. Wind shear has dropped to 20 - 25 knots, and will decrease to the moderate range, 10 - 20 knots, Saturday through Monday. The system will move over the Cape Verdes Islands over the weekend, bringing gusty winds and heavy rain squalls. NHC is giving the wave a 30% chance of developing by Sunday afternoon. Several models develop 99L into a tropical depression, but head it northwest into a region of very high wind shear that destroys the system by Wednesday.

Next post
I'll have an update Saturday by 1pm.

Jeff Masters

Hurricane

Earl spares North Carolina, heads for New England

By: JeffMasters, 3:07 PM GMT on September 03, 2010

Hurricane Earl sideswiped North Carolina's Outer Banks early this morning, passing just 75 miles east of Cape Hatteras. Special weather statements indicate that the only road out of the barrier island chain, Highway 12, is closed. Pounding waves over 15 feet high, on top of a storm surge of 2 - 3 feet, pushed water over the highway in multiple locations. Earl's winds also piled up huge waves offshore--waves peaked at 28 feet at the Diamond Shoals buoy, and at 31 feet at a buoy 150 nm offshore of Cape Hatteras. Peak wind gusts from Earl were 74 mph at 12:30am at Oregon Inlet, and 70 mph at Nags Head and Manteo. Sustained winds of 47 mph were recorded at Oregon Inlet, but sustained winds at Cape Hatteras never reached tropical storm force--top winds there were just 36 mph, with gusts to 62 mph. Radar estimated rainfall (Figure 2) for Earl from the Cape Hatteras, North Carolina radar shows that 3 - 4 inches of rain fell across much of the Outer Banks. Overall, aside from some significant beach erosion, Earl spared North Carolina.


Figure 1. MODIS image of Earl taken at 11:29am EDT September 2, 2010, by NASA's Terra satellite. At the time, Earl was a Category 3 hurricane with top winds of 125 mph. The storm had a somewhat lopsided shape, due to wind shear from the southwest affecting the storm. Image credit: NASA.

Earl is now headed to the north-northeast at 18 mph. Conditions will steadily improve today over North Carolina, but deteriorate over New England. Earl's outer rain bands have now reached New York's Long Island, as seen on long range Dover radar. Satellite imagery shows that Earl is no longer the impressive hurricane it once was. The eye is no longer visible, and the hurricane appears lopsided, due upper level winds out of the southwest that are creating a moderate 10 - 20 knots of wind shear. The latest 10:02am EDT eye report from the Hurricane Hunters showed that Earl continues to weaken, with a central pressure up to 961 mb. Top surface winds measured via their SFMR instrument were just 76 mph--barely Category 1 strength.


Figure 2. Radar estimated rainfall for Earl from the Cape Hatteras, North Carolina radar shows that 3 - 4 inches of rain fell across much of the Outer Banks.

Forecast for Earl
The latest set of model runs from 2am EDT (6Z) this morning show little change to Earl's track. Earl is expected to pass 20 - 50 miles southeast of Nantucket and Cape Cod, Massachusetts, at about 2am Saturday. The latest SHIPS model forecast of wind shear also shows no surprises. Wind shear will remain moderate, 10 - 20 knots today, then increase to the high range, 20 - 30 knots, on Saturday. Ocean temperatures will plunge to 20°C early Saturday morning, resulting in considerable weakening. Earl will still probably be a weak Category 1 hurricane early Saturday morning, when it will make its closest approach to New England. Earl is more likely to be a strong tropical storm early Saturday afternoon, when it is expected to make landfall in Nova Scotia or New Brunswick, Canada.


Figure 3. Wind field analysis of Hurricane Earl from 9:30am EDT Friday, September 3, 2010. Note the 15 mph asymmetry in Earl's wind field, caused by the storm's forward motion of 18 mph to the north-northeast at the time. The highest contour had top winds of 75 kt (87 mph) surrounding the "+" on the east side of Earl--the strong right front quadrant of the storm. However, winds on the left (west) side were just 65 knots (74 mph.) The asymmetry was greater--about 20 mph--at 6:30 am EDT this morning. Image credit: NOAA/AOML/Hurricane Research Division.

Impact of Earl on New England
The latest track forecasts still keep Earl's eye barely offshore of New England, with the center passing 20 - 60 miles southeast of Nantucket and the extreme eastern tip of Cape Cod, Massachusetts. The 11am NHC intensity forecast calls for Earl to have top winds of 75 mph at 2am Saturday, when the storm is expected to be at its closest to Massachusetts. Earl will be moving northeastward near 25 mph at that time, meaning that we will see a large difference in the winds between the weak and strong sides of this fast-moving hurricane. This difference is likely to be about 15 - 20 mph, based on the wind distribution around Earl's eye seen so far this morning. Winds analyzed on the experimental H*Wind product put out by NOAA's Hurricane Research Division at 9:30am this morning (Figure 3) showed that the winds on the weak left side of the storm were about 15 mph less than the winds in the powerful right front quadrant. Assuming Earl maintains this structure for the next day, we can expect the hurricane will have top winds of 75 mph on its strong southeast side over water when it whips by Southeast Massachusetts early Saturday morning, and winds of 55 - 60 mph in its northwest eyewall, closest to Massachusetts. If Cape Cod and Nantucket barely miss Earl's northwest eyewall, as currently forecast, top winds in those locations might only reach 45 - 50 mph. The latest NHC wind probability forecast from 11am this morning gives Nantucket a 12% chance of receiving sustained hurricane force winds of 74+ mph, and Hyannis on Cape Cod a 3% chance.

The highest storm surge from Earl is likely to be on the south side of Cape Cod Bay, due to the northeast winds that will be piling up water in the bay. NHC is giving a 10% chance that a storm surge of 3 - 5 feet will occur in Cape Cod Bay, but it is more likely that the surge will be 2 - 3 feet. The extreme western portion of Long Island Sound at New York City could see a storm surge bringing water levels 1 - 2 feet above ground level.


Figure 4. NHC is giving a 10% chance that the storm surge will reach heights of 3 - 5 feet in southern Cape Cod Bay. Image credit: National Hurricane Center.

Impact of Earl on Canada
Winds will begin to rise on the southwest coast of Nova Scotia late Friday night and early Saturday morning. By late morning Saturday, Earl is expected to make landfall somewhere between the Maine/New Brunswick border and central Nova Scotia. At that time, Earl will probably be a strong tropical storm with 55 - 60 mph winds. Earl will be moving at a very rapid 25 - 30 mph when it arrives in Canada, and regions on the right side of the eye can expect winds 15 - 20 mph greater than on the left side, due to the fast forward motion of the hurricane. Earl's impact is likely to be less than 2008's Hurricane Kyle, the last hurricane to hit Nova Scotia. Kyle hit near Yarmouth, Nova Scotia, as a Category 1 hurricane with 75 mph winds. Kyle produced a storm surge of 2.6 feet, and did $9 million in damage to Canada. The 11am EDT NHC wind probability forecast is calling for a 15% chance of hurricane-force winds in Yarmouth, and 3% in Halifax.

Fiona
There is not much to Tropical Storm Fiona, which satellite loops show to be a naked swirl of low clouds with just one diminishing spot of heavy thunderstorms on the southwest side of the circulation. High wind shear from Earl should continue to affect Fiona over the next two days, and be able to destroy the storm by Saturday.


Figure 5. Morning satellite image of Gaston's remains (left) and the latest tropical wave to move off of Africa (right).

Gaston may regenerate
Tropical storm Gaston lost its battle with dry air yesterday, degenerating into a disorganized low pressure area. Recent satellite imagery shows that Gaston's remains have developed a broad surface circulation again, and a few heavy thunderstorms have begun to appear. The latest SHIPS model forecast predicts shear will remain low to moderate, 5 - 15 knots, for the next five days, so it is possible Gaston could regenerate. The large amount of dry air surrounding Gaston's remains seen on water vapor satellite loops will continue to be a major impediment to development. NHC is giving Gaston a 40% chance of regenerating into a tropical depression by Sunday. I'd put these odds a little higher, at 60%. The GFS model develops Gaston and predicts it will move though the Lesser Antilles on Wednesday. The NOGAPS and Canadian models also indicate Gaston will re-develop, but move the storm slower and show it near the northern Lesser Antilles seven days from now.

New tropical wave
A large tropical off the coast of Africa is moving westward at about 10 mph, and has the potential to develop into a tropical depression next week. NHC is giving the wave a 10% chance of developing by Sunday afternoon. Wind shear is currently too high, 20 - 30 knots, for the wave to develop. However, once the wave reaches a point a few hundred miles from the Cape Verdes Islands two days from now, wind shear will drop and development will be more likely.

Next post
I'll have an update late this afternoon.

Jeff Masters

Hurricane

Category 2 Earl Heads for Cape Cod

By: JeffMasters, 9:49 AM GMT on September 03, 2010

Hi, Dr. Rob Carver with your early-morning blog update. Earl is starting to pass the Outer Banks, all tropical warnings south of Cape Lookout, NC have been discontinued, and the hurricane watch for North Carolina has been canceled. Looking at our METAR history page, it is apparent the low pressure center of Earl is now moving away from Cape Hatteras.

As of 500AM EDT, Earl is still a Category 2 storm with sustained winds of 105 mph. From the advisory, Earl is located at 35.3 N, 74.0 W, 85 miles east of Cape Hatteras, NC and 465 miles south-southwest of Nantucket, MA. On average, Earl is currently moving north-northeast at 20 mph. The minimum central pressure is now 955 mb. Data from TRMM (Fig. 1) and WSR-88D radar data (Fig. 2) show that Earl's eye is large and poorly-defined.


Fig. 1 Estimated rainfall-rate of Earl from TRMM taken at 2AM EDT 3 September 2010. Image courtesy of the Naval Research Lab


Fig. 2 Reflectivity image of Earl taken at 5am 3 September 2010. Doppler velocity scan showing the large-scale rotation of the storm.

Even though Earl's winds are declining, he still covers a very large area. Hurricane force winds extend 70 miles from the storm center and tropical storm force winds can be found 205 miles away. 12 foot seas extend at least 220 nmi from the center in all directions and may reach out to 420 nmi in the southeast quadrant of the storm. The most recent wind field analysis (930PM EDT) shows that the winds associated with Earl are weakening. Earl's integrated kinetic energy is 74 TJ, with a wind impact of 2.5 out of 6 and a storm surge impact of 4.3 out of 6.

Track/Intensity Forecast

NHC has not altered their track forecast for this update. Now that Earl has been captured by the trough, it will accelerate off to the northeast towards Nova Scotia. At the same time, shear from the trough and cooler surface waters continue to weaken Earl. This forecast weakening calls for Earl to be a category 1 storm when he passes Cape Cod this afternoon and when he makes landfall in Nova Scotia tomorrow.

Earl will pass by the mouth of the Chesapeake Bay later this morning, bringing tropical storm force winds to much of the Mid-Atlantic coast. Tropical storm force winds will arrive in coastal New England this afternoon, and hurricane force winds will arrive later this evening. You can track Earl's progress up the East Coast with our storm-centered radar animation.

Winds Forecast
NHC puts out a very useful wind probability forecast. Nantucket, MA looks to be the place most likely effected by Earl today, there is a 97% chance of TS force winds. Boston, Hyannis, and Providence, RI have a greater than 50% chance of tropical storm force winds today.

Current Watches and Warnings
Hurricane warnings are valid for the coast from Cape Lookout, NC to the NC/VA border and for eastern MA from Westport to Hull. Hurricane watches are in effect for Nova Scotia from Medway Harbour to Digby. Tropical storm warnings and watches cover parts of the Atlantic coast from the NC/VA border to Nova Scotia

For the latest information on watches and warnings for Earl in the US, visit our Tropical Alerts page. For people interested in watches and warnings for New Brunswick and Nova Scotia, visit Environment Canada's watches and warnings page.

Impacts
The threats from Earl have not changed significantly since my previous posting.

The primary threats from Earl are going to be surf, wind, and storm surge. The wind threat is going to be greatest in eastern MA since the passage of Earl is expected to bring hurricane force winds to Nantucket. Eastern Long Island will have the greatest winds outside of MA, with estimated winds of 30-40 mph, with gusts to 55 mph. This is expected to bring down trees and cause trouble for older mobile homes. People elsewhere along the Mid-Atlantic and New England coasts should expect weak tropical storm force winds (less than 35 mph).

For storm surge, 1-2 feet are expected along the NJ coast, with 3 feet possible in some locations. Eastern Long Island may have 2-4 feet surges along the Long Island Sound and Petonic and Gardines Bay. The Boston NWS office is not concerned about storm surge, but they note 20-25 foot seas are possible off Nantucket.

Since Earl is going to be moving quickly, flooding from rain should be confined to poor drainage areas and urban area street flooding.

For more localized info, check out the NWS Hurricane Local Statements or our severe weather page.

What to do
It's time to batten down the hatches. People living in New England have less than 12 hours to finish their preparations. Be sure to listen to local media for statements from emergency management agencies and the local NWS office.

Next update
Dr. Jeff Masters will have an update later this morning.

Hurricane

Category 2 Earl Passes the Outer Banks, Heads for Cape Cod

By: JeffMasters, 5:11 AM GMT on September 03, 2010

Hi, Dr. Rob Carver with your evening blog update. Earl continues to weaken, as he is now a category 2 storm.

Earl
As of 11PM EDT, Earl is a Category 2 storm with sustained winds of 105 mph. From the advisory, Earl is located at 33.8 N, 74.4 W, 115 miles south-southeast of Cape Hatteras, NC and 570 miles south-southwest of Nantucket, MA. On average, Earl is currently moving north-northeast at 18 mph. Data from hurricane hunter flights show that Earl's pressure has risen, the minimum central pressure is now 951 mb. Satellite data (Fig. 1), WSR-88D radar data (Fig. 2) and the hurricane hunters describe Earl's eyewall as being open in the west, which is to be expected for a weakening storm.


Fig. 1 Estimated rainfall-rate of Earl taken at 11PM EDT 2 September 2010. Image courtesy of the Naval Research Lab


Fig. 2 Reflectivity image of Earl taken at midnight 3 September 2010. Doppler velocity scan showing the large-scale rotation of the storm.

Even though Earl's winds are declinling, he still covers a very large area. Hurricane force winds extend 70 miles from the storm center and tropical storm force winds can be found 205 miles away. 12 foot seas extend at least 220 nmi from the center in all directions and may reach out to 420 nmi in the southeast quadrant of the storm. The most recent estimate (930PM EDT) of Earl's integrated kinetic energy is 91 TJ, with a wind impact of 3.0 out of 6 and a storm surge impact of 4.7 out of 6.

Track/Intensity Forecast

NHC has not really altered their track forecast for this update. The track has been adjusted to the east by a small amount. After Earl is captured by the trough in the jet stream Thursday, he will complete his turn to the northeast and start moving more rapidly. At the same time, shear from the trough and cooler surface waters will furthur weaken Earl. This forecast weakening calls for Earl to be a category 1 storm when he passes Cape Cod on Friday and when he makes landfall in Nova Scotia Saturday.

Right now, it looks like Earl is staying out to sea as it passes the Outer Banks. It will pass by the mouth of the Chesapeake Bay Friday morning. Tropical-storm force winds will start in Nantucket, MA Friday afternoon, and hurricane-force winds will arrive by late Friday evening.

Winds Forecast
NHC puts out a very useful wind probability forecast. Cape Hatteras has a 99% chance of tropical-storm (TS) force winds, and according to our M ETAR history page, the winds only need to pick up slightly. Besides the Outer Banks, Nantucket, MA looks to be the place most likely effected by Earl, there is a 90% chance of TS force winds. With the eastward shift in Earl's track, the area of 30% chance of TS force winds doesn't go as far inland as it did Wednesday night.

Current Watches and Warnings
Hurricane warnings are valid for the coast from Bogue Inlet, NC to the NC/VA border and for eastern MA from Westport to Hull. Hurricane watches are in effect from the NC/VA border to Cape Henlopen, DE and for Nova Scotia from Medway Harbour to Digby. Tropical storm warnings and watches cover the Atlantic coast from Cape Fear to Nova Scotia.

For the latest information on watches and warnings for Earl in the US, visit our Tropical Alerts page. For people interested in watches and warnings for New Brunswick and Nova Scotia, visit Environment Canada's watches and warnings page.

Impacts
The primary threats from Earl are going to be surf, wind, and storm surge. The wind threat is going to be greatest in eastern MA since the passage of Earl is expected to bring hurricane-force winds to Nantucket. Eastern Long Island will have the greatest winds outside of MA, with estimated winds of 30-40 mph, with gusts to 55 mph. This is expected to bring down trees and cause trouble for older mobile homes. Elsewhere between the Outer Banks and New England, expect weak tropical storm force winds (less than 35 mph).

For storm surge, 1-2 feet are expected along the NJ coast, with 3 feet possible in some locations. Eastern Long Island may have 2-4 feet surges along the Long Island Sound and Petonic and Gardines Bay. The Boston NWS office is not concerned about storm surge, but they note 20-25 foot seas are possible off Nantucket.

Since Earl is going to be moving quickly, flooding from rain should be confined to poor drainage areas and urban area street flooding.

For more localized info, check out NWS's Hurricane Local Statements or our severe weather page.

What to do
It's time to batten down the hatches. People living in New England have less than 18 hours to finish their preparations. Be sure to listen to local media for statements from emergency management agencies and the local NWS.

Next update
Dr. Jeff Masters will have an update Friday morning.

Hurricane

Earl significantly weakening

By: JeffMasters, 9:54 PM GMT on September 02, 2010

Hurricane Earl has significantly weakened today. The Hurricane Hunters found a central pressure of 948 mb at 4:06pm EDT, a large 20 mb rise from the 928 mb pressure of the 5am EDT advisory this morning. The aircraft found flight level winds at 10,000 feet of 124 mph, which translates to surface winds at the boundary between Category 2 and Category 3 strength, 112 mph. However, the SFMR instrument on the aircraft saw top surface winds of just 98 mph. Satellite imagery shows that Earl is no longer as impressive--the eye is less distinct, and the hurricane has a lopsided appearance. Dry air and wind shear of 15 - 20 knots have chewed away at Earl's southwest side.

Earl has made its turn to the north, and is headed for a close brush with North Carolina's Outer Banks. Rain bands from the hurricane have reached the coast, as seen on long-range Cape Hatteras radar.


Figure 1. Afternoon satellite image of Earl.

Forecast for Earl
If you're wondering about your chances for receiving hurricane force or tropical storm force winds from Earl, I highly recommend the NHC wind probability product. The highest odds of hurricane force winds for any location on the U.S. coast are for Nantucket--25%. Yarmouth, Nova Scotia has the highest odds for Canada, 15%, and Cape Hatteras has the highest odds for North Carolina, 19%. The latest set of model runs from 8am EDT (12Z) this morning show little change to Earl's track, and the latest SHIPS model forecast also shows no surprises. Wind shear will remain moderately high, 15 - 20 knots, through Friday morning. This should allow Earl to maintain Category 2 hurricane status as it passes North Carolina early Friday morning. By Friday night, as Earl gets caught in the jet stream and accelerates to the northeast, wind shear will rise to 20 - 30 knots and ocean temperatures will plunge to 20°C, resulting in considerable weakening. Earl will still probably be a Category 1 hurricane early Saturday morning, when it will make its closest approach to New England. Earl is more likely to be a strong tropical storm early Saturday afternoon, when it is expected to make landfall in Nova Scotia or New Brunswick, Canada. The expected impacts on the coast should somewhat less than what I outlined in this morning's blog post, because of Earl's recent weakening.


Figure 2. Wind field analysis of Hurricane Earl from 3:30pm EDT Thursday, September 2, 2010. Note the asymmetry in Earl's wind field, caused by the storm's forward motion of 18 mph to the north at the time. The highest contour has top winds of 80 kt (92 mph) surrounding the "+" on the NNE side of Earl--the strong right front quadrant of the storm. However, winds in the left front quadrant (on the west side) were just 75 knots (87 mph.) The asymmetry is not nearly as great as what was observed at 9:30am this morning. Image credit: NOAA/AOML/Hurricane Research Division.

Fiona
There is little change in the forecast for Tropical Storm Fiona, which is struggling due to high wind shear, courtesy of strong upper-level northerly winds from Hurricane Earl's outflow. Satellite loops show the classic signature of a tropical storm experiencing high wind shear--an exposed center of circulation, and all the heavy thunderstorms pushed to one side (the south side in this case). Wind shear from Earl and dry air should keep Fiona from attaining hurricane status, and the shear may be strong enough to destroy Fiona.

Gaston dies
Tropical Depression Gaston lost its battle with dry air. Satellite imagery shows that Gaston no longer has a surface circulation, and NHC has declared the system dead. The latest SHIPS model forecast predicts shear will remain low to moderate, 5 - 15 knots, for the next five days, so it is possible Gaston could regenerate.


Figure 3. Afternoon satellite image of Gaston (left) and the latest tropical wave to move off of Africa (right).

New tropical wave
A large and well-organized tropical wave moved off the coast of Africa last night, and this wave has the potential to follow the pattern set by Danielle, Earl, Fiona, and Gaston. Several models do develop this system into a tropical depression early next week, and NHC is giving the wave a 10% chance of developing by Saturday afternoon. Wind shear is currently too high, 30 - 40 knots, for the wave to develop. However, once the wave reaches a point a few hundred miles southwest of the Cape Verdes Islands two days from now, wind shear will drop and development will be more likely.

There is also a tropical wave over Central Africa which will emerge from the coast in 4 - 5 days. Some of the models are predicting development of this wave, 7 or so days from now.

Links to follow today
Cape Hatteras weather
Cape Hatteras radar

Next post
I'll have an update in the morning, and Dr. Rob Carver will have a late-night update.

Jeff Masters

Hurricane

Earl: 3rd strongest hurricane on record so far north in U.S. coastal waters

By: JeffMasters, 3:36 PM GMT on September 02, 2010

Hurricane Earl strengthened significantly overnight, and its Category 4 140 mph winds make it the third strongest Atlantic hurricane on record so far north in U.S. coastal waters. Only Hurricane Esther of 1961 and Hurricane Connie of 1955 made it farther north in U.S. coastal waters at a higher strength. Both storms had winds 5 mph stronger than Earl--145 mph. One other Atlantic hurricane was stronger than Esther and Connie at a more northerly latitude--the second storm of 1922, which had winds of 150 mph. However, this hurricane was far out at sea, north of Bermuda.

Earl has made its turn to the north, and is headed for a close brush with North Carolina's Outer Banks. Rain bands from the hurricane are now visible on long-range Cape Hatteras radar, and these rain bands will begin to spread over coastal North Carolina this afternoon. Recent satellite imagery shows an extremely impressive major hurricane, that will be resistant to sudden changes in intensity.


Figure 1. MODIS image of Earl taken at 2pm EDT September 1, 2010, by NASA's Aqua satellite. Image credit: NASA.

Forecast for Earl
The latest set of model runs from 2am EDT (6Z) this morning show little change to Earl's track. The latest SHIPS model forecast shows wind shear will remain moderate, 10 - 15 knots, through Friday morning. This should allow Earl to maintain major hurricane status as it passes North Carolina early Friday morning. By Friday night, as Earl gets caught in the jet stream and accelerates to the northeast, wind shear will rise to 20 - 30 knots and ocean temperatures will plunge to 20°C, resulting in considerable weakening. Earl will still probably be a Category 2 hurricane early Saturday morning, when it will make its closest approach to New England. Earl is more likely to be a Category 1 hurricane early Saturday afternoon, when it is expected to make landfall in Nova Scotia, Canada.


Figure 2. Wind field analysis of Hurricane Earl from 9:30am EDT Thursday, September 2, 2010. Note the asymmetry in Earl's wind field, caused by the storm's forward motion of 18 mph to the north-northwest at the time. The highest contour has top winds of 110 kt (130 mph) surrounding the "X" on the NNE side of Earl--the strong right front quadrant of the storm. However, winds in the left front quadrant (on the SSW side) were just 80 - 85 knots (92 - 97 mph.) Image credit: NOAA/AOML/Hurricane Research Division.

Earl is a large hurricane, which gives it a higher potential for storm surge damage than a smaller hurricane with the same top winds. One measure of a storm's power, useful for gauging storm surge threat, is to measure the speed of the winds and multiply by the area over which those winds blow. This total is called the Integrated Kinetic Energy (IKE). Based on the storm's IKE, one can come up with a scale from 0 - 6 rating the storm's destructive power from its storm surge. A separate rating can be given to the destructive potential of the storm's winds. The IKE value of 99 Terrajoules for Earl, at 9:30am EDT today, gives its storm surge a destructive power of 4.9 on a scale of 0 - 6. Earl's winds have a similar destructive power, 4.9 on a scale of 0 - 6. Let's hope the right front quadrant of Earl, where the main storm surge would occur, stays offshore! For comparison, the small Category 5 Hurricane Camille of 1969 had an IKE of 80 Terrajoules, and the very large Category 2 Hurricane Ike of 2008 had an IKE of 116 Terrajoules, higher than Category 4 Earl's.

Impact of Earl on North Carolina
Earl's eye is expected to stay offshore of North Carolina. However, much of coastal North Carolina will experience tropical storm-force winds of 39+ mph for a period of 12 - 18 hours beginning this afternoon or early this evening. Earl's expected radius of hurricane-force winds of 90 miles to the west may bring hurricane conditions to the Outer Banks, but probably not to mainland North Carolina. Earl's radius of tropical storm-force winds to the west, over land, will probably be about 150 miles, so locations from Wilmington to Norfolk could see sustained winds of 40 mph. Storm surge will likely be less than two feet along the North Carolina coast west of Cape Hatteras facing the open ocean, since winds will be offshore. However, a significant storm surge of 3 - 5 feet can be expected on the south side of Pamlico Sound, due to strong northerly winds. A 3 - 5 foot storm surge is also likely along the Outer Banks from Cape Hatteras northward 50 miles to Nags Head. NHC is giving a 10% chance that the storm surge will reach 7 - 9 feet along the coast near Nags Head. It is possible that Coastal Highway 12 out of the Outer Banks will be blocked by sand and debris, or washed out, resulting in a multi-day period where everyone on the Outer Banks will be stranded. Since Earl's forward speed will be about 20 mph as it passes Cape Hatteras, the winds on the hurricane's west side will be about 40 mph less than on the east side (Figure 2.) (I regret that I misstated this yesterday. To think about this, imagine a stationary hurricane with 120 mph winds on all sides. Now, put the hurricane in motion. The winds are still 120 mph on all sides, relative to a frame of reference that moves with the storm, but an observer on the ground will see 140 mph winds in the right front quadrant, and 100 mph on the left side.) The NHC wind probability forecast is calling for a 13% chance of hurricane-force winds on Cape Hatteras, 1% for Morehead City, and no chance for Norfolk, Virginia.


Figure 3. NHC is giving a 10% chance that the storm surge will reach heights of 7 - 9 feet along the Outer Banks of North Carolina near Nags Head. Image credit: National Hurricane Center.

Impact of Earl on New England
Residents in Eastern Long Island, Rhode Island, and Southeast Massachusetts need to complete all of their hurricane preparations by early Friday morning. By Friday afternoon, winds will rise quickly. Earl's recent increase in strength means that New England will see a stronger hurricane than was expected. The latest track forecasts still keep the eye barely offshore, or have it passing over Nantucket and the extreme eastern tip of Cape Cod, Massachusetts. The 5am NHC intensity forecast calls for Earl to have top winds of 100 mph at 2am Saturday, when the storm is expected to be over or just offshore of the eastern tip of Cape Cod. Earl will be moving near 25 mph at that time, meaning that that top sustained winds on the north side of the eye, over land, will be 50 mph, and the winds will be 100 mph on the south side over water. NHC is giving a 10% chance that a storm surge of 3 - 5 feet will occur in Long Island Sound (Figure 4), and 2 - 3 feet along the south coast of Long Island. A small deviation in Earl's track to the left, resulting in a direct hit on eastern Long Island and Providence, Rhode Island, would probably be a $10+ billion disaster, as the hurricane would hit a heavily populated area and drive a 7 - 15 foot storm surge up Buzzards Bay and Narragansett Bay. The odds of this occurring are around 3%, according to the latest NHC wind probability forecast. The forecast is calling for a 28% chance of hurricane-force winds on Nantucket, 7% in Providence, 4% in Boston, 7% in Eastport, Maine, and 17% in Hyannis.


Figure 4. NHC is giving a 10% chance that the storm surge will reach heights of 3 - 5 feet from Long Island Sound to Southeast Massachusetts. Image credit: National Hurricane Center.

Impact of Earl on Canada
Winds will begin to rise on the southwest coast of Nova Scotia early Saturday morning, and all preparations need to be completed by Friday night. By late morning Saturday, Earl is expected to make landfall somewhere between the Maine/New Brunswick border and central Nova Scotia. At that time, Earl will probably be a Category 1 hurricane. Earl will be moving at a very rapid 25 - 30 mph when it arrives in Canada, and regions on the right side of the eye can expect winds 50 - 60 mph greater than on the left side, due to the fast forward motion of the hurricane. It is unlikely that Earl will be as damaging as Hurricane Juan, the 2003 Category 2 hurricane which made a direct hit on Halifax, Nova Scotia, causing over $200 million in damage. Earl's impact is likely to be greater than 2008's Hurricane Kyle, the last hurricane to hit Nova Scotia. Kyle hit near Yarmouth, Nova Scotia, as a Category 1 hurricane with 75 mph winds. Kyle produced a storm surge of 2.6 feet, and did $9 million in damage to Canada. The NHC wind probability forecast is calling for a 14% chance of hurricane-force winds in Yarmouth, and 4% in Halifax.

Beach erosion
Regardless of Earl's exact track, the U.S. East Coast can expect a long period of high waves today and Friday. Significant beach erosion and dangerous rip currents will be the rule, due to waves that will reach 10 - 15 feet in offshore waters. Waves are expected to reach 25 - 30 feet along the Cape Hatteras, North Carolina shore tonight. Beach erosion damage in the mid-Atlantic states will likely run into the millions, but will probably not be as bad as that suffered during Nor'easter Ida in November of 2009. That storm (the remains of Hurricane Ida that developed into a Nor'easter) remained off the coast for several days, resulting in a long-duration pounding of the shore that caused $300 million in damage--$180 million in New Jersey alone.

Fiona
Tropical Storm Fiona is struggling due to high wind shear, courtesy of strong upper-level northerly winds from Hurricane Earl's outflow. Satellite loops show the classic signature of a tropical storm experiencing high wind shear--an exposed center of circulation, and all the heavy thunderstorms pushed to one side (the south side in this case). Wind shear from Earl and dry air should keep Fiona from attaining hurricane status over the next two days. The shear may be strong enough to destroy Fiona, as predicted by the NHC. However, by this weekend, Earl may pull far enough away for shear to drop and Fiona to survive. It is possible Fiona may pose a threat to Bermuda on Saturday or Sunday.

Gaston
Tropical Depression Gaston has lost most of its heavy thunderstorms this morning, as it battles dry air. Water vapor satellite images show a large area of dry air to the north and west of Gaston, and this dry air will be the dominant inhibiting factor for development for the next few days. The latest SHIPS model forecast predicts shear will remain low to moderate, 5 - 15 knots, for the next five days. Assuming Gaston can fight off the dry air--which seems likely, given the low shear--the storm should be able to intensify into a hurricane by Sunday, as predicted by the many of the intensity models. Gaston appears likely to threaten the Lesser Antilles Islands as early as Tuesday. Historically, 25% of all tropical cyclones at Gaston's current position have gone on to hit the U.S. East Coast.

Special Hurricane Earl Update At 4:30 pm EDT on the Weather Underground Broadcast Network
The Weather Underground Broadcast Network will air a special edition of the Daily Downpour featuring meteorologists Rob Carver, Tim Roche, Shaun Tanner, and myself. This live update will feature the most up-to-date information on this dangerous storm and its possible effects on the East Coast.

There will be a three ways to contact the show panelists:

1. Call 415-983-2634 to ask specific questions about anything tropical related.

2. Send an email to broadcast@wunderground.com, and your email may be read on the air.

3. The chat room on the Weather Underground Broadcast Network homepage will be monitored throughout the broadcast for any related questions.

Lastly, if you are along the East Coast somewhere that could be affected by Hurricane Earl, we want to hear from you during the broadcast. Tell us what local officials are doing to prepare for Earl, and how it is affecting you. Please call 415-983-2634 or email broadcast@wunderground.com with your experiences.

Listen to the live, special broadcast beginning 4:30 p.m. EDT, 1:30 p.m PDT, by going to the Weather Underground Broadcast Network.

Links to follow today
Cape Hatteras weather
Cape Hatteras radar

Next post
I'll have an update late this afternoon.

Jeff Masters

Hurricane

Category 4 Earl Approaches the East Coast

By: JeffMasters, 5:49 AM GMT on September 02, 2010

Hi, Dr. Rob Carver with your evening blog update. It's a busy night in the tropics with category 4 Hurricane Earl and Tropical Storms Fiona and Gaston in the Atlantic. We'll focus on Earl tonight.

Earl
As of 11PM EDT, Earl is a Category 4 storm with sustained winds of 140 mph and faster gusts. From the advisory, Earl is located at 27.8 N, 73.8 W, 520 miles south-southeast of Cape Hatteras, NC. On average, Earl is currently moving north-northwest at 18 mph. Data from hurricane hunter flights show that Earl's pressure has fallen, the minimum central pressure is now 932 mb. Looking at Figure 1, an estimate of rainfall rates (think radar in space), we see a complete eyewall, with an especiallly vigorous thunderstorm cluster in the northwest quadrant. These


Fig. 1 Estimated rainfall-rate of Earl taken at 9PM EDT 1 September 2010. Image courtesy of the Naval Research Lab

Earl is still a large storm. Hurricane force winds extend 90 miles from the storm center and tropical storm force winds can be found 230 miles away. 12 foot seas extend at least 210 nmi from the center in all directions and may reach out to 450 nmi in the northeast quadrant of the storm. The most recent estimate (930PM EDT) of Earl's integrated kinetic energy is 91 TJ, with a wind impact of 3.1 out of 6 and a storm surge impact of 4.7 out of 6. Like Dr. Masters said earlier today, if the right front quadrant of Earl stays out to sea, the storm surge may not be as significant as this rating indicates.

Track Forecast
NHC has not really altered their track forecast for this update. Thanks to the subtropical high, Earl will continue turning toward the north as it moves around the subtropical high. When the trough in the jet stream comes out on Thursday, Earl will accelerate quickly to the northeast. The timing of the trough's arrival will determine Earl's impact on the East Coast. If the trough comes out quickly, Earl will stay at sea. If the trough is late in arriving, it could move Earl across the East Coast.

That said, the current forecast still holds that Earl's center will stay out to sea, but with Earl's center passing near the Outer Banks late Thursday night, then passing the Delmarva peninsula Friday morning before flying past Cape Cod Friday night and crossing over Canada's Nova Scotia Saturday. There is also a small possibility (less than 10%) that Earl could pass directly over the Outer Banks and/or the Delmarva peninsula. However, with a storm of Earl's size, the center does not have to pass overhead to cause damage. Please keep this in mind when considering your hurricane preparations.

Winds Forecast
Earl's size and track will produce tropical-storm force winds somewhere along the East Coast this weekend, and there is a 28% chance of hurricane-force winds along the Outer Banks. NHC puts out a very useful wind probability forecast. The highlights are that Cape Hatteras, NC has a 28% chance of hurricane-force winds and a 91% chance of tropical-storm (TS) force winds. A wide swath of 30+% probabilities covers the East Coast from Virginia to New England. Cities with a greater than 40% chance of TS winds include Norfolk, Ocean City, Providence, Boston, and Nantucket. Halifax, Nova Scotia in Canada has a 62% chance of TS force winds.

Earl is expected to maintain its current intensity until it meets the trough and starts moving northeastwards. The shear from the trough will start weakening it. It will likely go by Cape Cod as a fast-moving category 2 hurricane. When it goes over Nova Scotia, it will likely still be a tropical storm.
Current Watches and Warnings

Hurricane warnings are valid for the coast from Bogue Inlet, NC to the NC/VA border. Hurricane watches in effect from the NC/VA border to Cape Henlopen, DE and from Woods Hole, MA to Sagamore Beach, MA. Tropical storm warnings and watches cover much of the coast in between the NC/VA border and Woods Hole, MA. For the latest information on watches and warnings for Earl, visit our Tropical Alerts page.

Impacts
The primary threats from Earl are going to be storm surge, surf, and wind. Since Earl is forecast to gain speed after meeting the trough, flooding from rain should not be a large problem. From a broad perspective, storm surges are expected to be 3-5 feet above the tidal level, with large breaking waves at the coast. Beach erosion along the Delmarva peninsula and Outer Banks (8-10 foot breaking waves) could be significant. For more localized info, check out NWS's Hurricane Local Statements or our severe weather page.

What to do
People living in areas covered by the watches and warnings should be working through their hurricane preparation plans now. You have less than 24 hours to complete your preparations if you are in the Outer Banks and less than 48 hours in New England. Be sure to listen to local media for statements from emergency management agencies and the local NWS.

Fiona
All watches and warnings for Fiona were discontinued by the 5:00 PM EDT forecast. Fiona is forecast to curve northward without affecting land and dissipate in 4 days.

Gaston
Once Earl moves past Nova Scotia, this is the storm to watch in the tropical Atlantic. While it is far out at sea (more than 6 days to affect land), some computer models suggest Gaston could affect the Bahamas or the Caribbean. Statistical intensity forecast models (LGEM and SHIPS) rapidly intensify Gaston, but the dynamical models (HWRF, GFDL) do not. This storm will be worth watching over the next week or so.

Aerial Reconnaissance
The skies around Earl are going to be very busy Thursday according to the Tropical Cyclone Plan of the Day. There will be 3 flights from the Hurricane Hunters. NCAR and NOAA's Gulfstream's will be flying around Earl. HRD's WP-3D's will be flying research missions every 12 hours. NASA is sending several aircchraft as part of their Genesis and Rapid Intensification Processes (GRIP) mission. Their Global Hawk UAV will be flying for at least 24 hours. NASA's DC-8 has a six-hour mission scheduled. Finally, a WB-57 (one of the planes I supported during 2001's CRYSTAL-FACE) will also be flying high above Earl with microwave remote sensing gear. NASA has a nice list of the airborne instruments.


Fig. 2 Photo of Earl's eyewall taken from NASA's DC-8 Image Credit: NASA/Jane Peterson. (Full size image)

Next update
Dr. Jeff Masters will have an update Thursday morning. Dr. Masters, myself, Shaun Tanner, and myself will be participating in a special Hurricane Haven Thursday afternoon to discuss Earl's imminent approach. Dr. Masters will have the finalized details in his blog update.

Hurricane

Earl a Category 4 storm again

By: JeffMasters, 9:23 PM GMT on September 01, 2010

Hurricane Earl has regained Category 4 strength this afternoon, and continues on a steady northwest path towards the North Carolina coast. Recent satellite imagery shows that Earl has become more symmetrical, with improved upper-level outflow and no signs of dry air wrapping into the core. The improved appearance is probably due to lower wind shear. Latest wind shear tendency imagery from the University of Wisconsin CIMSS group shows that shear on the southwest side of Earl has fallen by about 10 knots over the past 24 hours.


Figure 1. Afternoon satellite image of Earl.

Forecast for Earl
The latest set of model runs from 8am EDT (12Z) this morning shows little change to Earl's track. Thus, my write-up of the possible impacts to North Carolina, New England, and Canada in this morning's post remain unchanged. The latest SHIPS model forecast shows wind shear will remain moderate, about 15 knots, through Friday afternoon. This should allow Earl to maintain major hurricane status as it passes North Carolina early Friday morning. By Friday night, as Earl gets caught in the jet stream and accelerates to the northeast, wind shear will rise to 20 - 30 knots and ocean temperatures will plunge to 20°C, resulting in considerable weakening. Earl will still probably be a Category 1 or 2 hurricane early Saturday morning, when it will make its closest approach to New England. Earl is more likely to be a strong tropical storm or weak Category 1 hurricane early Saturday afternoon, when it is expected to make landfall in Nova Scotia, Canada.

Earl is a large hurricane, which gives it a higher potential for storm surge damage than a smaller hurricane with the same top winds. One measure of a storm's power, useful for gauging storm surge threat, is to measure the speed of the winds and multiply by the area over which those winds blow. This total is called the Integrated Kinetic Energy (IKE). Based on the storm's IKE, one can come up with a scale from 0 - 6 rating the storm's destructive power from its storm surge. A separate rating can be given to the destructive potential of the storm's winds. The IKE value of 112 Terrajoules for Earl, at 3:30pm EDT today, gives its storm surge a destructive power of 5.0 on a scale of 0 - 6. Earl's winds have a lower destructive power, 3.4 on a scale of 0 - 6. Let's hope the right front quadrant of Earl, where the main storm surge would occur, stays offshore! For comparison, the small Category 5 Hurricane Camille of 1969 had an IKE of 80 Terrajoules, and the very large Category 2 Hurricane Ike of 2008 had an IKE of 116 Terrajoules--similar to Category 3 Earl's.

Fiona
Tropical Storm Fiona is struggling due to high wind shear, courtesy of strong upper-level northerly winds from Hurricane Earl's outflow. The latest Hurricane Hunter center fix at 1:29pm EDT found Fiona had weakened some, with a central pressure of 999 mb. This is a rise of 1 mb from this morning. The wind shear analysis from the University of Wisconsin CIMSS group shows that shear has increased to a moderately high 15 - 20 knots this afternoon. Satellite loops show the classic signature of a tropical storm experiencing high wind shear--an exposed center of circulation, and all the heavy thunderstorms pushed to one side (the south side in this case). Martinique radar shows that the outer bands from Fiona are bringing heavy rain squalls to the same islands of the northern Lesser Antilles that were affected by Earl. Our wundermap for the northern Lesser Antilles shows no stations recorded winds over 20 mph this afternoon, though there was no reporting station on Barbuda, the island closest to Fiona.

Forecast for Fiona
Moderate wind shear and dry air should keep Fiona from attaining hurricane status over the next two days, as big brother Earl continues to bring high wind shear. The shear may be strong enough to destroy Fiona, as predicted by the NHC. However, by this weekend, Earl may pull far enough away for shear to drop and Fiona to survive. The 4 - 5 day track forecast is highly uncertain, as there is a large spread in the model solutions. It is possible Fiona may pose a threat to Bermuda on Saturday or Sunday, and the storm could wander for a week or more in the waters between Bermuda and the U.S. East Coast.


Figure 2. Afternoon satellite image of Fiona.

Tropical Storm Gaston forms
Tropical Storm Gaston developed enough heavy thunderstorms near its center this afternoon to get a name, and appears destined to become Hurricane Gaston by early next week. Water vapor satellite images show a large area of dry air to the north and west of Gaston, and this dry air will be the dominant inhibiting factor for development. The latest SHIPS model forecast predicts shear will remain moderate, 10 - 15 knots, for the next four days, and perhaps fall to the low range 4 - 5 days from now. Gaston is over warm 28°C waters, and should be able to steadily intensify into a hurricane by Saturday or Sunday, as predicted by the many of the intensity models. Gaston may threaten the northern Lesser Antilles Islands as early as Tuesday.

Next post
I'll have an update in the morning, and Dr. Rob Carver will have a late night update tonight.

Jeff Masters

Hurricane

Hurricane warnings for North Carolina for Category 3 Earl

By: JeffMasters, 3:21 PM GMT on September 01, 2010

Hurricane warnings are flying for the coast of North Carolina, as Hurricane Earl chugs to the northwest at 17 mph. Earl has weakened some over the past day, thanks to an eyewall replacement cycle and some dry air that got wrapped into the core of the storm. Earl's eye made a direct hit on NOAA buoy 41046 at 4am EDT this morning. The buoy recorded a surface pressure of 943 mb, exactly what the Hurricane Hunters were estimating. The buoy measured winds in the eyewall of 76 mph, gusting to 96 mph. The peak winds of Earl were stronger than this, though, since the buoy only reported measurements once per hour, which is not a fine enough resolution to see the peak winds. The buoy is also located at a height of 5 meters, which is less than the standard ten meter height used to do wind measurements, so an additional upward adjustment needs to be made. Peak waves at the buoy were a remarkable 49 feet.

A recent microwave "radar in space" image (Figure 2) shows that dry air has spiraled into the core of Earl, knocking a gap into the southern eyewall. The latest 9am EDT report from the Hurricane Hunters confirmed that the southwest portion of the eyewall was missing. Top winds seen by the Hurricane Hunters were only Category 2 strength, and Earl may be weaker than the stated 125 mph winds in the 11am NHC advisory.


Figure 1. Image of Hurricane Earl taken by astronaut Douglas Wheelock aboard the International Space Station on Tuesday, Aug. 31, 2010.

>
Figure 2. Microwave "radar in space" image of Hurricane Earl taken at 6:45am EDT Wednesday, September 1, 2010. The southern portion of Earl's eyewall was missing, thanks to a slug of dry air (blue colors) that had spiraled into Earl's core.

Intensity forecast for Earl
Recent satellite loops show that upper level outflow is good to the north and east of Earl, but is poor on the southwest side. The latest SHIPS model forecast shows that this is because upper level winds out of the southwest are creating 15 - 20 knots of wind shear on Earl's southwest side. The winds are from a trough of low pressure to Earl's west. This trough is forecast to weaken and move to the west away from Earl, which should reduce the shear to 10 - 15 knots by Thursday morning. If true, the relaxation in shear may give Earl enough time to mix out the dry air it ingested and regain its previous 135 mph Category 4 intensity. Water vapor satellite loops, though, show there is still plenty of dry air on Earl's west side that could potentially wrap into the storm if there is enough wind shear to drive it into Earl's circulation. Ocean temperatures are still very high, a near-record 29.5 - 30°C, and very warm waters extend to great depth, resulting in a total ocean heat content favorable for intensification. It is likely Earl will be a Category 2 or 3 hurricane at its closest approach to North Carolina Thursday night and Friday morning, with a small chance it will be at Category 4 strength. By Friday night, when Earl will be making its closest approach to New England, wind shear will rise to a high 20 - 30 knots and ocean temperatures will plunge to 20°C, resulting in considerable weakening. Earl will still probably be a Category 1 or 2 hurricane on Friday night, when it could potentially make landfall in Massachusetts. Earl is more likely to be a strong tropical storm or weak Category 1 hurricane on Saturday morning, when it could potentially make landfall in Maine or Nova Scotia, Canada.

Impact of Earl on North Carolina
The latest set of computer models runs from 2am EDT (6Z) this morning are very similar to the previous set of runs. The NOGAPS model brings Earl closest to the coast, predicting the west eyewall of the the hurricane will hit the Outer Banks of North Carolina near 2am Friday. If this track verifies, a period of 40+ mph winds will affect coastal North Carolina for a period of 12 - 18 hours beginning at about 6pm EDT Thursday night. Earl's expected radius of hurricane-force winds of 60 miles to the west will bring hurricane conditions as far west as Morehead City and Elizabeth City in North Carolina. Earl's radius of tropical storm-force winds to the west, over land, will probably be about 150 miles, so locations from Wilmington to Norfolk could see sustained winds of 40 mph in this worst-case model scenario. Storm surge would not be significant along the North Carolina coast facing the open ocean, since winds would be offshore. However, a significant storm surge of 3 - 6 feet could occur in Pamlico Sound, due to strong west to north winds. Coastal Highway 12 out of the Outer Banks would likely be blocked by sand and debris or washed out, resulting in a multi-day period where everyone on the Outer Banks would be stranded. Is is possible that the NOGAPS scenario is not the worst case, and that Earl will strike farther west, resulting in the Outer Banks getting the fearsome maximum winds of the storm's right front quadrant. However, it is more likely that Earl will pass just offshore, resulting in North Carolina receiving the weaker west side winds. Since Earl's forward speed will be about 20 mph at that time, the winds on the hurricane's west side will be about 40 mph less than the right front quadrant on the east side. The NHC wind probability forecast is calling for a 23% chance of hurricane-force winds on Cape Hatteras, 7% for Morehead City, and 3% for Norfolk, Virginia.

Impact of Earl on New England
The NOGAPS model brings Earl closest to the coast of New England, predicting the west eyewall of the the hurricane will pass over Nantucket at about 2am Saturday morning, and the tip of Cape Cod a few hours later. If this track verifies, 40+ mph winds would affect southeastern Massachusetts for a period of 6 - 12 hours beginning at about 8pm EDT Friday night. Earl should be a weaker Category 1 or 2 hurricane then, with hurricane-force winds extending 30 miles to the left of its track. Hurricane conditions would then affect the eastern tip of Long Island, coastal Rhode Island, and Southeast Massachusetts. Earl's radius of tropical storm-force winds to the north, over land, will probably be about 150 miles, so locations from Central Long Island to southern Boston would experience sustained winds of 40 mph in this worst-case model scenario. A storm surge of 3 - 5 feet might occur in Long Island Sound, and 2 - 3 feet along the south coast of Long Island. A deviation to the left, with a direct hit on eastern Long Island and Providence, Rhode Island, would probably be a $10 billion disaster, as the hurricane would hit a heavily populated area and drive a drive a 5 - 10 foot storm surge up Buzzards Bay and Narragansett Bay. The odds of this occurring are around 5%, according to the latest NHC wind probability forecast. The forecast is calling for a 25% chance of hurricane-force winds on Nantucket, 8% in Providence, 6% in Boston, and 18% in Hyannis. Keep in mind that the average error in position for a 3-day NHC forecast is 185 miles, which is about how far offshore Earl is predicted to be from New England early Saturday morning.

Impact of Earl on Canada/Maine
Late morning Saturday, Earl is expected to make landfall somewhere between the Maine/New Brunswick border and central Nova Scotia. At that time, Earl should be a strong tropical storm or weak Category 1 hurricane. This won't be another Hurricane Juan, the 2003 Category 2 hurricane which made a direct hit on Halifax, Nova Scotia, causing over $200 million in damage. Earl's impact is likely to be closer to 2008's Hurricane Kyle, which hit near Yarmouth, Nova Scotia, as a Category 1 hurricane with 75 mph winds. Kyle produced a storm surge of 2.6 feet, and did $9 million in damage to Canada. The NHC wind probability forecast is calling for a 29% chance of hurricane-force winds in Yarmouth, 24% in Halifax, and 17% in Eastport, Maine.

Beach erosion
Regardless of Earl's exact track, the U.S. East Coast can expect a long period of high waves beginning on Thursday. Significant beach erosion and dangerous rip currents will be the rule, due to waves that will reach 10 - 15 feet in offshore waters. Beach erosion damage in the mid-Atlantic states will likely run into the millions, but will probably not be as bad as that suffered during Nor'easter Ida in November of 2009. That storm (the remains of Hurricane Ida that developed into a Nor'easter) remained off the coast for several days, resulting in a long-duration pounding of the shore that caused $300 million in damage--$180 million in New Jersey alone.

Record ocean temperatures off the U.S. Mid-Atlantic Coast
The period May - July was the hottest such 3-month period in history for the Northeast and Southeast U.S., according to NOAA's National Climatic Data Center. Most of the hurricane-prone states along the coast, including New Hampshire, Massachusetts, Rhode Island, New Jersey, Delaware, Maryland, Virginia, North Carolina, and South Carolina had their hottest May - July in the 116-year record. These record air temperatures led to record ocean temperatures, according to an analysis I did of monthly average 5x5 degree SST data available from the UK Met Office Hadley Centre.. The region of ocean bounded by 35N - 40N, 75W - 70W, which goes from Cape Hatteras, North Carolina to Central New Jersey, had the warmest July ocean temperatures since records began in 1875--a remarkable 2.12°C (3.8°F) above average. The year 2008 was a distant second place, with temperatures 1.5°C (2.7°F) above average. The ocean region off the Southeast U.S. coast, bounded by 30N - 35N, 80W - 75W, from the Georgia-Florida border to Cape Hatteras, North Carolina, had its 4th warmest July ocean temperatures on record. Temperatures were 0.8°C (1.4°F) above average, which fell short of the record 1.1°C anomaly of 1944. The August numbers are not available yet, but will probably show a similar story.

All this warm water off the East Coast means it is much easier for a major hurricane to make landfall in the mid-Atlantic or Northeast U.S. Usually, ocean temperatures fall below the 26.5°C threshold needed to support a hurricane as soon as a storm pushes north of Cape Hatteras, North Carolina. This year, those temperatures extend all the way to the New Jersey coast (Figure 3.) Such warm ocean temperatures increase the odds of a major hurricane making it to the mid-Atlantic or New England coasts. Since record keeping began in 1851, there have been only 15 major hurricane in U.S. coastal waters north of the North Carolina/Virgina border--about one per decade. The last such storm was Hurricane Alex of August 6, 2004.


Figure 3. Water surface temperatures from AVHRR satellite data for the 6-day period ending August 31, 2010. Ocean temperatures of 26.5°C, capable of supporting a hurricane, stretched almost to Long Island, New York. Image credit: Ocean Remote Sensing Group, Johns Hopkins University Applied Physics Laboratory.

Fiona
Tropical Storm Fiona last night showed us why hurricane forecasting is such a difficult job. The storm made an unexpected slow-down in forward speed. This slow-down resulted in less wind shear affecting Fiona than expected, since the storm is farther from the upper-level outflow of Hurricane Earl. The wind shear analysis from the University of Wisconsin CIMSS group shows just a moderate 10 - 20 knots of shear affecting Fiona, which is low enough that the storm has been able to organize into a respectable 60 mph tropical storm. Martinique radar shows that the outer bands from Fiona are bringing heavy rain squalls to the same islands of the northern Lesser Antilles that were affected by Earl. Our wundermap shows that winds in the islands are all below 20 mph, but winds will increase to 30 - 40 mph later today as Fiona draws closer. Satellite loops show that heavy thunderstorm activity has decreased some in recent hours. This may be due to the fact that Fiona is currently crossing the cold water wake of Earl.

Forecast for Fiona
In the short term, moderate wind shear and dry air should keep Fiona from attaining hurricane status, though we do have several models that predict it could become a Category 1 hurricane. Fiona is likely to come close enough to Bermuda on Saturday or Sunday to pose a threat to that island, though it is possible high wind shear from Earl could kill the storm by then. The long term fate of Fiona remains unclear, with some models calling for dissipation this weekend, and other models calling for Fiona to be left behind by Earl to wander over the ocean near Bermuda early next week.


Figure 4. Morning radar image of Fiona from the Martinique radar. Image credit: Meteo France.

TD 9
Invest 98L gained enough heavy thunderstorm activity to be classified as Tropical Depression Nine this morning. This wil probably be Tropical Storm Gaston by tomorrow morning. The latest SHIPS model forecast predicts shear will remain moderate, 10 - 15 knots, for the next five days, and TD 9 could be a Category 1 hurricane five days from now, as predicted by the GFDL model. The storm will likely pose a threat to the northern Lesser Antilles Islands by Tuesday.

Next post
I'll have an update this afternoon.

Jeff Masters

Hurricane

Category 3 Earl Continues Moving Towards the East Coast

By: JeffMasters, 4:13 AM GMT on September 01, 2010

Hi, Dr. Rob Carver with your evening blog update. It's a busy night in the tropics with Hurricane Earl and Tropical Storm Fiona in the Atlantic, and 3 named storms in the western Pacific. Tonight, though, we'll focus on Earl.

As of 11PM EDT, Earl is still a Category 4 storm with sustained winds of 130 mph and gusts of 160 mph. From the advisory, Earl is located at 23.0 N, 69.9 W, 910 miles south-southeast of Cape Hatteras, NC. On average, Earl is currently moving towards the northwest at 14 mph. Remember, large storms are known for having wobbly tracks. Aircraft observations and microwave imagery (Fig. 1) indicate that the eyewall is reforming.


Fig. 1 Estimated rain-rate of Earl taken at 2332Z 31 Aug 2010. Image courtesy of the Naval Research Lab

Earl is passing near buoy 41046 and is generating some large waves as shown by Figure 1.


Fig. 2Plot of wave heights observed at buoy 41046. Data courtesy of the National Data Buoy Center

Earl is a large storm. Hurricane force winds extend 90 miles from the storm center and tropical storm force winds can be found 200 miles away. This means Earl will have an impact on areas well away from the center's track

Track Forecast
NHC has not really altered their track forecast for this update. Thanks to the subtropical high, Earl will continue a slight turn to the right as it moves around the subtropical high. Then when a trough in the jet stream comes out on Thursday, Earl will accelerate quickly to the northeast. The timing of the trough's arrival will determine Earl's impact on the East Coast. The current forecast still holds that Earl's center will stay out to sea, and I don't see any reason to disagree. Most of the computer model guidance supports this forecast (except for NOGAPS and NGFDL, and they have Earl only crossing the Outer Banks). It is worth noting that the ECMWF global model (the best global model) does bring Earl close to the Outer Banks. Earl will make his closest approach to the Outer Banks sometime early Friday morning.

Winds Forecast
Earl's size and track will likely produce tropical-storm force winds somewhere along the East Coast this weekend. From the wind probability product issued by NHC, Cape Hatteras has a 63% chance of tropical-storm force winds sometime this weekend. There is a wide swath of 30% chance of TS winds from Virginia north towards Maine. New York City has a 20% chance of TS winds, and Nantucket, MA has a 50% chance.

When Earl hooks on to the trough and starts accelerating to the northeast, it will start transitioning from a tropical system to an extratropical low. This means it will start weakening.

Current Watches
As of 1045PM EDT, a hurricane watch is in effect for the coastal US from Surf City, NC to the NC/VA border. Remember, this means tropical-storm force winds are expected within 48 hours. A tropical storm warning has been issued for the Turks and Caicos islands. A tropical storm watch is also in effect from Cape Fear to Surf City and for the southeastern Bahama islands. For the latest information on watches and warnings for Earl, visit our Tropical Alerts page.

Impacts
It's too early to be specific. That said, the local NWS office in Morehead City, NC thinks that with the combination of tides and winds, a storm surge of 4 feet is possible along the Outer Banks with moderate coastal flooding possible. They also think rip currents are a likely threat at the beaches.

What to do
People living in areas covered by the hurricane watch should start following their hurricane preparation plans now. You have less than 48 hours to complete your preparations. Be sure to listen to local media for statements from emergency management agencies and the local NWS. If you live in areas prone to flooding, evacuate to a hurricane shelter or a place outside evacuation zones. If an evacuation order is given, please follow it.

People living from Virginia to New England should monitor the progress of Earl and think about their hurricane preparations.

Fiona
Fiona stayed too close to big brother Earl and is paying the price. Outflow from Earl is expected to create shear, transforming Fiona into an open trough. It's forecast to dissipate in 2-3 days.

600AM EDT UPDATE
Earl has weakened to a category 3 storm with maximum winds of 125 mph. NHC has extended the hurricane watch from the NC/VA border to Parramore island. The track forecast has shifted a bit to the west, so the chance of tropical-storm force winds in the New England area has gone up. For example, Eastport ME has a greater than 50% chance of tropical storm force winds now. For more cities, take a look at the wind probabilities product. Intensity forecast is relatively unchanged.

Fiona is starting to build a little more space between herself and Earl. If this keeps up, Fiona might have a shot at survival. This is worth keeping an eye on.

Next update
Dr. Jeff Masters will have an update Wednesday morning.

Hurricane


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Category 6™

About

Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather