Dr. Jeff Masters' WunderBlog

Texas drought could last 9 years; Ophelia a Cat 3; Cat 4 Nalgae nears Philippines

By: JeffMasters, 2:52 PM GMT on September 30, 2011

The devastating Texas drought that has already cost over $5 billion could continue for nine more years, predicted Texas State Climatologist John Nielson-Gammon in an interview with Reuters yesterday. "It is possible that we could be looking at another of these multi-year droughts like we saw in the 1950s, and like the tree rings have shown that the state has experienced over the last several centuries," Nielson-Gammon said. Drought statistics released yesterday by the U.S. Drought Monitor showed that over 96% of Texas is experiencing the two worst categories of drought, extreme and exceptional. The past 12 months have been the driest one-year period on record in Texas. The main blame for this year's drought can be put on La Niña, the cooling of equatorial Pacific waters that deflects the jet stream and takes rain-bearing low pressure system away from Texas. Other large-scale atmospheric/oceanic patterns called the Pacfic Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) have also favored dry conditions for Texas this year. When the AMO brings warm ocean temperatures to the North Atlantic, as it has since 1995, Texas is typically dry. Texas also tends to be dry when the PDO brings cool ocean temperatures to the coastal North Pacific next to North America. This has been the case since 2007 (except for late 2009 and early 2010.) In a post earlier this month in his excellent blog, Climate Abyss, Nielson-Gammon has this to say about the influence of global warming on the 2011 drought:

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

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


Figure 1. This week's Drought Monitor showed that over 96% of Texas was experiencing the two worst categories of drought, extreme and exceptional. Image credit: U.S. Drought Monitor.

High fire danger for Texas today
Strong winds, temperatures in the 90s, and relative humidities in the 15 - 25% range will bring critical fire conditions today to Texas in the Austin-San Antonio region today, according to the Storm Prediction Center. Austin set a record high for the date yesterday, when the mercury climbed to 99°. Dry weather will dominate Texas for the coming week, but an increasing flow of moist air off the Gulf of Mexico next weekend may allow for a little drought relief 7 - 10 days from now. Texas' hurricane season is pretty much over; it is rare for tropical storms to affect Texas this late in the season. There is the potential the state could get moisture from an Eastern Pacific tropical storm, but there are probably only going to be 1 - 3 more storms in the Eastern Pacific this year, since activity in the basin is sharply lower during La Niña events.

Ophelia strengthens into the season's fourth hurricane
Hurricane Ophelia has strengthened into an respectable Category 3 hurricane with 115 mph winds, making it the season's fourth hurricane and third major hurricane. The arrival of the season's fourth hurricane on September 29 is a week later than the average date for the season's fourth hurricane, which is September 21. This is a remarkably late date for a season boasting the 2nd greatest number of named storms ever recorded before October (sixteen). Typically, over 60% of all named storms intensify into hurricanes; this year, the percentage has been only 25%. This bizarre combination of a near-record number of named storms but only four hurricanes has led to a near-average year for total destructive potential, as measured by the Accumulated Cyclone Energy (ACE). We are about 7% above average for ACE for this point in the season, according to stats compiled by Dr. Ryan Maue. The combination of near-record warm sea surface temperatures but exceptionally dry, stable air over the tropical Atlantic responsible for this year's odd hurricane season shows no signs of changing over the next few weeks. However, it's worth pointing out that the ocean regions north of 20°N latitude where Ophelia and Philippe are positioned have near-normal levels of atmospheric stability and dry air.


Figure 2. Morning satellite image of Ophelia.

Recent satellite loops show that Ophelia continues to intensify. The hurricane has a prominent eye, good upper-level outflow, and solid lower-level spiral banding. Moderate wind shear due to upper-level west-southwesterly winds is slowing intensification, and shear is expected to remain moderate through Sunday. The models agree that Ophelia will track far enough to the east of Bermuda that the island should see sustained winds below 45 mph, since it will be on the weak (left) side of the storm. The 11 am wind probability forecast from NHC gave Bermuda a 30% chance of receiving tropical storm force winds, and just a 1% chance of receiving hurricane force winds. Ophelia's closest approach to the island will be late Saturday night and early Sunday morning. Ophelia is likely to bring high winds and heavy rains to Southeast Newfoundland Monday, though the models have been trending towards keeping Ophelia farther offshore from Newfoundland in their recent runs. The 11 am wind probability forecast for Cape Race, Newfoundland gave it a 36% chance of receiving tropical storm force winds, and a 1% chance of hurricane force winds.

Tropical Storm Philippe
In the middle Atlantic, Tropical Storm Philippe continues to struggle against dry air and wind shear. Satellite loops show Philippe is a small system with little heavy thunderstorm activity, with the surface circulation exposed to view by wind shear. Wind shear is expected to increase to a very high 30 - 40 knots Saturday through Monday, thanks to the upper-level outflow from Ophelia. This shear may be high enough to destroy Philippe by Monday, though most of the models predict Philippe will survive the shear for the next five days. In the event Philippe does survive the shear, the storm could penetrate far enough west that Bermuda might need to be concerned with it, since Philippe will be forced almost due west by a strong ridge of high pressure early next week. There is even a small chance (perhaps 5%) that Philippe could make a comeback from Ophelia's high shear and affect the U.S. East Coast or Bahama Islands late next week.

Elsewhere in the Atlantic, none of the computer models is calling for a new tropical storm to form in the coming seven days. The large-scale environment over the Atlantic currently favors sinking air, due to the current phase of the Madden-Julian Oscillation (MJO). This situation will likely last well into next week, and will discourage formation of new tropical storms. The MJO is a 30 - 60 day cycle of thunderstorm activity that affects the tropics.


Figure 3. Satellite-predicted rainfall amounts for the 24-hour period ending at 2 am EDT Saturday October 1, 2011, for Typhoon Nalgae. The typhoon is expected to dump 4 - 8 inches of rain over Northern Luzon in the Philippines. This is probably an underestimate, given Nalgae's recent rapid intensification from Cat 2 to Cat 4. Image credit: NOAA/NESDIS.

Typhoon Nesat drenching Vietnam; Category 4 Typhoon Nalgae drenching the Philippines
Typhoon Nesat hit Vietnam today near Hanoi as a strong tropical storm with 70 mph winds. Nesat roared across Luzon Island in the Philippines Monday as a powerful Category 3 typhoon with 120 mph winds, leaving 43 people dead and 30 missing. The Philippines has a very bad case of deja-vu today, with Typhoon Nalgae already beginning to dump heavy rains on the main island of Luzon. Nalgae is expected to follow a track almost exactly the same as Nesat's, passing over Luzon just to the north of the capital of Manila. Nalgae is expected to maintain its Category 4 strength until landfall, and will likely bring at least 4 - 8 inches of rain to Northern Luzon. While this may not be as wet a storm as Nesat, Nalgae's rains will be falling on soils already saturated from Nesat's heavy rains, and the potential exists for high loss of life due to extreme flooding and mudslides. Wind damage is also a huge concern; Nagae's 135 mph winds are capable of causing widespread destruction on Luzon.

Jeff Masters

Drought Hurricane

Updated: 3:00 PM GMT on September 30, 2011

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Ophelia strengthening; Typhoon Nalgae a new threat to the Philippines

By: JeffMasters, 1:51 PM GMT on September 29, 2011

Tropical Storm Ophelia is strengthening as it pulls away from the Lesser Antilles Islands and heads north-northwest. Recent satellite loops show that Ophelia has developed a Central Dense Overcast (CDO) of high cirrus clouds over its core, which is characteristic of strengthening tropical storms that are nearing hurricane intensity. Dry air and moderate wind shear of 15 - 20 knots are slowing down Ophelia's intensification, but by Friday morning, wind shear is expected to fall to 10 - 15 knots, and remain below 15 knots through Sunday morning. This should allow Ophelia to intensify into a hurricane on Friday. Most of the models agree that Ophelia will track far enough to the east of Bermuda that the island should see sustained winds below 45 mph, since it will be on the weak (left) side of the storm. We can't rule out the possibility that Bermuda will receive hurricane force winds yet, but the odds are low--the 5 am wind probability forecast from NHC gave Bermuda just a 3% chance of receiving hurricane force winds. Ophelia's closest approach to the island will be late Saturday night and early Sunday morning. Ophelia is likely to bring high winds and heavy rains to Southeast Newfoundland Sunday night, as a weakening tropical storm.

In the middle Atlantic, Tropical Storm Philippe is headed west-northwest, and is not expected to trouble and land areas. Satellite loops show Philippe is a small system with little heavy thunderstorm activity. Wind shear is expected to diminish some today over the storm, which should allow the storm to intensify. However, by Saturday, Philippe will be encountering very high wind shear of 30 - 40 knots associated with the upper-level outflow from Ophelia. This shear will probably be high enough to destroy Philippe by Monday. In the event Philippe does survive the shear, the storm could penetrate far enough west that Bermuda might need to be concerned with it.

Elsewhere in the Atlantic, none of the computer models is calling for a new tropical storm to form in the coming seven days. The large-scale environment over the Atlantic currently favors sinking air, due to the current phase of the Madden-Julian Oscillation (MJO). This situation will likely last well into next week, and will discourage formation of new tropical storms. The MJO is a 30-60 day cycle of thunderstorm activity that affects the tropics.


Figure 1. Morning satellite image of Ophelia, showing the large Central Dense Overcast (CDO) that has formed.

Typhoon Nesat battering China
Typhoon Nesat hit China's Hainan Island today as a Category 1 typhoon with 75 mph winds. While Nesat's winds and storm surge will not cause major damage, it is a very wet storm, capable of dropping up to 8 inches of rain in 24 hours, according to latest satellite rainfall forecasts. Haikou on Hainan Island recorded a wind gust of 78 mph and 3.23" of rain as the eyewall passed just to the north. Nesat will hit Vietnam near Hanoi as a tropical storm on Saturday.

Nesat roared across Luzon Island in the Philippines Monday as a powerful Category 3 typhoon with 120 mph winds, leaving 35 people dead and 45 missing. The Philippines has a new worry today: Typhoon Nalgae has formed 700 miles to the east of Luzon Island, and is expected to follow a course just to the north of Nesat's. Nalgae is expected to intensify into a major Category 3 typhoon and hit the northern portion of Luzon on Saturday afternoon, local time. With soils on the island already saturated from the heavy rains Nesat brought, the new typhoon promises to bring heavy flooding to Luzon this weekend.


Figure 2. True-color MODIS image of Typhoon Nesat over the South China Sea taken at 1:35 pm local time September 28, 2011. At the time, Nesat was a Category 1 typhoon with 75 mph winds. Image credit: NASA.

Jeff Masters

Hurricane

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Ophelia regenerates; Typhoon Nesat heads towards China

By: JeffMasters, 11:39 AM GMT on September 28, 2011

Ophelia is back as a tropical depression, thanks to a reduction in wind shear that allowed the storm to re-organize yesterday afternoon just east of the Lesser Antilles Islands. Martinique radar shows a large area of concentrated thunderstorms lies about 200 miles to the east of the northern Lesser Antilles, with good spiral banding and rotation. Recent satellite loops show that Ophelia's heavy thunderstorms are not increasing, and are limited in areal extent. The low-level center is partially exposed to view, thanks to strong wind shear. No hurricane hunter flights are scheduled for today.


Figure 1. Morning radar image from the Martinique radar shows the heavy rain showers from Ophelia, just east of the northern Lesser Antilles. Image credit: Meteo-France.

Dry air and moderate wind shear of 15 - 20 knots are slowing down Ophelia's intensification, and will continue to do so through Thursday. By Friday, wind shear is expected to fall to 10 - 15 knots, and most of the models give strong support to Ophelia intensifying into a hurricane by Saturday. With the models all agreeing on at track for Ophelia just east of Bermuda, Tropical Storm Warnings will probably be required for the island this weekend. Bermuda will be on the left (weak) side of Ophelia, so will miss the storm's strongest winds and heaviest rains. Ophelia may be a threat to Southeast Newfoundland early next week.

In the far eastern Atlantic, Tropical Storm Philippe is headed northwest into the middle of the North Atlantic, and is not expected to trouble and land areas. Wind shear is high enough over Philippe that the storm may dissipate by 4 - 5 days from now.

Typhoon Nesat headed towards China
Typhoon Nesat is headed west towards a landfall on China's Hainan Island on Thursday, and in northern Vietnam just south of Hanoi on Friday. Nesat is a large but disorganized Category 1 storm, and will not have time to strengthen significantly before landfall. However, Nesat is a very wet storm, capable of dropping over a foot of rain in 24 hours, according to latest satellite rainfall forecasts. Nesat roared across Luzon Island in the Philippines Monday as a powerful Category 3 typhoon with 120 mph winds, leaving 20 people dead and severe flooding problems.


Figure 2. Predicted rainfall amounts for the 24 hours ending at 06 UTC on Thursday September 29 show the Nesat is expected to dump over a foot of rain (red colors) along where its southern eyewall tracks. Image credit: NOAA/NESDIS.

Eastern Pacific's Hurricane Hilary steadily weakening
In the Eastern Pacific, Hurricane Hilary has weakened to a Category 1 hurricane with 90 mph winds. Continued weakening will occur over the next few days, and all of the models show Hilary dissipating before reaching the coast. Moisture from Hilary will not reach the U.S.

Jeff Masters

Hurricane

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Typhoon Nesat kills 12 in the Philippines; Ophelia regenerating

By: JeffMasters, 1:28 PM GMT on September 27, 2011

Typhoon Nesat roared across Luzon Island in the Philippines last night as a dangerous Category 3 typhoon with 120 mph winds. The typhoon likely dumped 12 - 15 inches of rain along portions of it path, according to satellite rainfall amount forecasts. Flooding and drownings been blamed for at least 12 deaths in the Philippines. We don't have any weather stations on the east coast of Luzon near where the eye came ashore that survived to send us data, but winds at Iba on the west coast of Luzon reached a sustained speed of 67 mph at 5 pm local time today as the eyewall of Nesat moved through. Cabanatuan in Central Luzon received 5.55" inches of rain. The center of Nesat passed well north of the capital of Manila, which received sustained winds of 37 mph, gusting to 55, and 2.74" of rain. Heavy flooding is reported in Manila, where the soils were saturated by heavy seasonal monsoon rains before the arrival of Nesat. Nesat's winds drove a storm surge that smashed through the seawall protecting Manila, and significant storm surge flooding occurred along the shore. Nesat is now a disorganized Category 1 typhoon with 95 mph winds over the South China Sea, and is expected to re-intensify into a Category 2 typhoon before making landfall near China's Hainan Island on Thursday and northern Vietnam on Friday.


Figure 1. Microwave image from NOAA's F-16 satellite showing the estimated rain rate of Typhoon Nesat as it was making landfall on Luzon Island in the Philippines at 6:31 pm EDT Monday, September 26, 2011. Rainfall rates over 1"/hour (orange colors) were occurring in much of the eyewall. Image credit: Navy Research Lab, Monterey.

Atlantic update: Ophelia rising again, Philippe no threat
The remains of Tropical Storm Ophelia continue to fester in the Atlantic a few hundred miles east of the northern Lesser Antilles Islands, and now appear ready to re-organize into a tropical depression. Martinique radar shows a large area of concentrated thunderstorms lies about 200 miles to the east of the northern Lesser Antilles, though with only a little rotation and very limited spiral banding. Recent satellite loops show that Ophelia may now have a closed surface circulation, and heavy thunderstorms are increasing, though are limited in areal extent. A hurricane hunter aircraft will investigate Ophelia this afternoon at 2 pm to see if a tropical depression has formed.


Figure 2. Morning radar image from the Martinique radar shows the heavy rain showers from Ophelia, just east of the northern Lesser Antilles. Image credit: Meteo-France.

Dry air and moderate wind shear of 10 - 20 knots are slowing down the regeneration process, and will continue to limit Ophelia's intensification over the next few days. NHC gave Ophelia an 80% chance of regenerating by Thursday in their 8 am Tropical Weather Outlook, and most of the models give strong support to Ophelia regenerating. I expect Ophelia will be a tropical storm again by Wednesday. A trough of low pressure should steer Ophelia to the northwest and then north over the next five days, with the storm making its closest pass by Bermuda on Saturday. Tropical Storm Warnings may be required for Bermuda this weekend. Ophelia is not a threat to any other land areas, though the storm will bring some heavy rain squalls and wind gusts of 25 - 35 mph to the northern Lesser Antilles Islands today and Wednesday.

In the far eastern Atlantic, Tropical Storm Philippe is headed northwest into the middle of the North Atlantic, and is not expected to trouble and land areas. Wind shear is high enough over Philippe that the storm is unlikely to become a hurricane over the next five days.

Eastern Pacific's Hurricane Hilary slowly weakening
In the Eastern Pacific, Hurricane Hilary has slowly weakened to a Category 3 hurricane with 115 mph winds. A trough of low pressure is expected to turn Hilary to sharply to the north on Wednesday. Since Hilary will be crossing cool water and encountering increased wind shear, the storm will weaken rapidly beginning Wednesday, and all of the models show Hilary dissipating before reaching the coast.


Figure 3. MODIS satellite image of Hurricane Hilary at 4:35 pm EDT September 26, 2011. At the time, Hilary was a Category 3 storm with 130 mph winds. Image credit: NASA.

Jeff Masters

Hurricane

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Ophelia dies; Philippe, Hilary no threat; Nesat drenching the Philippines

By: JeffMasters, 12:07 PM GMT on September 26, 2011

High wind shear and dry air finally managed to kill off Tropical Storm Ophelia yesterday. The storm's remnants continue to fester a few hundred miles east of the Northern Lesser Antilles Islands, but dry air and moderate wind shear of 10 - 20 knots should make any regeneration of Ophelia slow. NHC gave Ophelia a 20% chance of regenerating by Wednesday in their 8 am Tropical Weather Outlook. In the far eastern Atlantic, Tropical Storm Philippe is headed west-northwest into the middle of the North Atlantic, and is not expected to trouble any land areas. Philippe is the 16th named storm this year, tying 2011 with 2008, 2003, and 1936 for 7th place for the most number of named storms in a year. Philippe's formation date of September 24 puts 2011 in 2nd place for earliest date of arrival of the season's 16th storm. Only 2005 had an earlier 16th storm. With only three of this year's sixteen storms reaching hurricane strength so far, though, this year has been near average for destructive potential. Atlantic hurricane records go back to 1851. Philippe has a modest chance to become the season's fourth hurricane; the 5 am EDT NHC wind probability forecast gave Philippe a 23% chance of intensifying into a hurricane by Tuesday afternoon. Wind shear is expected to steadily increase today to 15 - 20 knots, limiting Philippe's chances to become a hurricane.


Figure 1. MODIS satellite image of Hurricane Hilary at 2:25 pm EDT September 25, 2011. At the time, Hilary was a Category 3 storm with 125 mph winds. Image credit: NASA.

Eastern Pacific's Hurricane Hilary slowly weakening
In the Eastern Pacific, Hurricane Hilary has slowly weakened to a Category 3 hurricane with 120 mph winds. A trough of low pressure is expected to turn Hilary to sharply to the north on Wednesday, but most of the models do not bring Hilary ashore over Mexico's Baja Peninsula during the next five days. Since Hilary will be crossing cool water and encountering increased wind shear on its journey north, the storm is likely to be no stronger than a tropical depression if it does manage to reach the coast.


Figure 2. Microwave image from NASA's TRMM satellite showing the estimated rain rate of Typhoon Nesat at 4:56 am EDT Monday September 26, 2007. Rainfall rates of up to 0.8"/hour (yellow colors) were occurring along the southeast quadrant of the eyewall. Image credit: Navy Research Lab, Monterey.

Typhoon Nesat nears landfall in the Philippines
Typhoon Nesat, a Category 1 typhoon with 90 mph winds, is just a few hours from landfall near Casiguran on Luzon Island in the Philippines. Nesat was expected to intensify to a major Category 3 storm before landfall, but the typhoon ingested a large pulse of dry air that got wrapped into the core of the storm, slowing down intensification. The typhoon still has time to intensify into a Category 2 storm, but Nesat's wind and storm surge will not cause major devastation. Heavy rains from Nesat are a major concern, though. Recent microwave satellite images (Figure 2) show rains up to 0.8" per hour falling along the southeast quadrant of Nesat's center, and heavy rains of 5 - 10 inches will cause significant flooding in the Philippines. Nesat will lose strength during its crossing of the Philippines, but is expected to regain strength as it crosses the South China Sea before making another landfall near China's Hainan Island on Thursday.

Jeff Masters

Hurricane

Updated: 1:52 PM GMT on September 26, 2011

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Ophelia barely alive; Philippe forms; dangerous Typhoon Nesat aims at Philippines

By: JeffMasters, 4:16 PM GMT on September 25, 2011

Tropical Storm Ophelia is barely alive today, as high wind shear and dry air continue to take their toll on the storm. Satellite imagery shows that Ophelia has an oval, highly-stretched center of circulation, with almost no heavy thunderstorm activity near the center. Most of the storm's heavy thunderstorms are to the east of the center, with just a few puffs of thunderstorms occasionally popping up near the center. An analysis from the University of Wisconsin CIMMS group shows a high 25 - 30 knots of wind shear due to strong upper-level southwesterly winds. Water vapor satellite images show Ophelia is at the eastern edge of large area of very dry air.


Figure 1. Noon satellite image of Ophelia. It's tough to pick out a low-level center, and all of the storm's heavy thunderstorms lie several hundred miles to the east of the center. Ophelia is barely alive.

Forecast for Ophelia
The latest SHIPS model forecast predicts wind shear will drop to the moderate range, 15 - 20 knots, tonight through Tuesday morning. If Ophelia survives until tonight, the lower shear should allow the storm to make a bit of a comeback. Bermuda is the only land area that might be threatened by Ophelia, but it remains questionable whether or not Ophelia will still be a tropical storm when it makes its closest pass by Bermuda late in the week.

Philippe forms in the far eastern Atlantic
Tropical Storm Philippe formed in the far eastern Atlantic off the coast of Africa yesterday. Philippe is the 16th named storm this year, tying 2011 with 2008, 2003, and 1936 for 7th place for the most number of named storms in a year. Philippe's formation date of September 24 puts 2011 in 2nd place for earliest date of arrival of the season's 16th storm. Only 2005 had an earlier 16th storm. With only three of this year's sixteen storms reaching hurricane strength so far, though, this year has been near average for destructive potential. Atlantic hurricane records go back to 1851. Philippe has a chance to become the season's fourth hurricane; the 11 am EDT NHC wind probability forecast gives Philippe a 45% chance of intensifying into a hurricane by Tuesday morning. Philippe is headed northwest and then north towards cooler waters, and is not a threat to any land areas.


Figure 2. MODIS satellite image of Hurricane Hilary at 1:40 pm EDT September 24, 2011. At the time, Hilary was a Category 4 storm with 140 mph winds. Image credit: NASA.

Eastern Pacific's Hurricane Hilary weakens to Category 3 strength
In the Eastern Pacific, Hurricane Hilary weakened slightly to a Category 3 hurricane with 125 mph winds. Hilary is headed west, away from Mexico, and the storm is small enough that its outer bands are not causing flooding problems for Mexico. A trough of low pressure expected to move over the Western U.S. by the middle of the week should be strong enough to turn Hilary to the north, eventually bringing Hilary to Mexico's Baja Peninsula. The timing of when Hilary might hit Baja is highly uncertain, though. The ECMWF model keeps Hilary offshore for the next 7 days, while the latest 06Z runs of the GFS and NOGAPS models predict Hilary could hit Central Baja on Friday.

Dangerous Typhoon Nesat headed for the Philippines
What may be the season's most dangerous storm in the Western Pacific, Typhoon Nesat, is headed west at 10 mph towards Luzon Island in the Philippines. Nesat is just a Category 1 typhoon with 80 mph winds, but has favorable conditions for intensification. Shear is a moderate 10 - 15 knots, Nesat is embedded in a very moist environment, has very warm sea surface temperatures of 30°C under it, and a very favorable upper-level outflow pattern above it. Nesat has plenty of time to intensify into a major Category 3 or 4 typhoon before its expected landfall on Luzon Island in the Philippines near 9 am local time Tuesday morning.

Jeff Masters

Hurricane

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Ophelia remains weak; TD 17 forms; dangerous Nesat headed for the Philippines

By: JeffMasters, 4:54 PM GMT on September 24, 2011

There's not much change to Tropical Storm Ophelia today, which continues to battle dry air and high wind shear. Satellite imagery shows that Ophelia has little heavy thunderstorm activity near its low level circulation center, which is mostly exposed to view. Most of the storm's heavy thunderstorms are to the east of the center, with just a few puffs of thunderstorms occasionally popping up near the center. An analysis from the University of Wisconsin CIMMS group shows a high 20 - 25 knots of wind shear due to strong upper-level southwesterly winds. Water vapor satellite images show Ophelia is at the eastern edge of large area of very dry air.


Figure 1. Afternoon satellite image of Ophelia showing the low-level center exposed to view, with all the storm's heavy thunderstorms in a band several hundred miles to the east and south. This is not a healthy-looking tropical storm.

Forecast for Ophelia
The latest SHIPS model forecast predicts that Ophelia will experience high wind shear of 20 - 40 knots over the next five days, and will move into a region with slightly drier air. This combination of shear and dry air may be enough to dissipate Ophelia, as predicted by several of the models. However, Ophelia has maintained itself better than the models have predicted, so the storm will probably survive until at least Sunday. Even it Ophelia does dissipate, it will have the chance to regenerate by Tuesday or Wednesday, when it may encounter a region of lower wind shear. At this time, it appears that Ophelia will only be a threat to Bermuda.

TD 17 forms
Tropical Depression 17 formed in the far eastern Atlantic off the coast of Africa last night, and is likely to intensify into Tropical Storm Philippe later today. TD 17 has some impressive low-level spiral bands and upper-level outflow, and is very close to tropical storm strength. The predicted west-northwest to northwest track of TD 17 will put it in a position where historically, very few storms have ever gone on to hit land.


Figure 2. MODIS satellite image of Hurricane Hilary at 4:05 pm EDT September 23, 2011. At the time, Hilary was a Category 4 storm with 145 mph winds. Image credit: NASA.

Powerful Hurricane Hilary remains at Category 4 strength
In the Eastern Pacific, Hurricane Hilary remains an impressive Category 4 hurricane with 140 mph winds. Hilary is headed west, away from Mexico, and the storm is small enough that its outer bands are not causing flooding problems for Mexico. A trough of low pressure expected to move over the Western U.S. by the middle of the week may be strong enough to turn Hilary to the north, eventually bringing Hilary to Mexico's Baja Peninsula. The timing of this event is highly uncertain, though. Hilary is small enough that it is unlikely to bring significant drought relief to Arizona, New Mexico, and Texas if the storm's remnants move north into those states. Hilary is the fourth Category 4 hurricane in the Eastern Pacific this year, and the second strongest, behind Hurricane Dora, which had 155 mph winds.

Invest 91L set to soak North Carolina
A moderate amount of heavy thunderstorm activity has developed over the Northwestern Bahamas in association with the tail end of an old stalled front. This disturbance, Invest 91L, is under a low 5 - 10 knots of wind shear, but water vapor loops show a considerable amount of dry air to the east and west of the disturbance that will likely interfere with development. In their 8 am Tropical Weather Outlook, NHC gave 91L a 20% chance of developing into a tropical depression by Monday. The disturbance has only a short window to develop, as it is headed northwards and is expected to make landfall in North Carolina by Sunday afternoon. The 8 am EDT SHIPS model forecast predicts 91L will hit 35 knots of wind shear by Sunday morning, when the storm will be approaching the coast of North Carolina. Heavy rains from 91L may cause localized flooding in Morehead City, NC and surrounding regions. A moist flow of tropical air over the region has already brought rainfall amounts of 1 - 3 inches to much of Eastern North Carolina today.

Dangerous Tropical Storm Nesat headed for the Philippines
What may be the season's most dangerous storm in the Western Pacific, Tropical Storm Nesat, has formed about 700 miles east of the Philippine Islands. Nesat is under a moderate 10 knots of wind shear, is embedded in a very moist environment, has very warm sea surface temperatures of 30°C under it, and a very favorable upper-level outflow pattern above it. Nesat has plenty of time to intensify into a major typhoon before its expected landfall on Luzon Island in the Philippines on Tuesday morning.

I'll have an update before 2 pm Sunday afternoon.

Jeff Masters

Hurricane

Updated: 5:39 PM GMT on September 24, 2011

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Ophelia weakening; Hilary an impressive Cat 4

By: JeffMasters, 2:09 PM GMT on September 23, 2011

Tropical Storm Ophelia is weaker today, thanks to dry air and high wind shear. Satellite imagery shows that Ophelia has almost no heavy thunderstorms near its low level circulation center, which is entirely exposed to view. Most of the storm's heavy thunderstorms are in a band several hundred miles to the east and south, with just a few puffs of thunderstorms occasionally popping up near the center. An analysis from the University of Wisconsin CIMMS group shows a high 20 - 25 knots of wind shear due to strong upper-level southwesterly winds. Water vapor satellite images show the center of Ophelia is entirely within a large area of very dry air. We don't have any current buoy, ship, or hurricane hunter observations of Ophelia; the Hurricane Hunters will be making their first flight into Ophelia this afternoon near 2 pm EDT.


Figure 1. Morning satellite image of Ophelia showing the low-level center exposed to view, with all the storm's heavy thunderstorms in a band several hundred miles to the east and south. This is not a healthy-looking tropical storm.

Forecast for Ophelia
The latest SHIPS model forecast predicts that Ophelia will experience high wind shear of 20 - 30 knots over the next five days, and will move into a region with drier air. I believe that the combination of shear and dry air will probably dissipate Ophelia on Saturday or Sunday, as predicted by the ECMWF, GFS, and NOGAPS models. Ophelia will bring a few heavy rain squalls to the Lesser Antilles on Saturday and Sunday. At longer ranges, even if Ophelia dissipates this weekend, it could encounter a lower-shear environment south of Bermuda early next week and regenerate. Ophelia (or its remnants) may may pass close to Bermuda as early as Wednesday. Ophelia may eventually be a threat to Canada, but it is too early to know.


Figure 2. Morning satellite image of Hurricane Hilary at Category 4 strength, with 145 mph winds. Quite a contrast from Ophelia!

Hurricane Hilary hits Category 4 strength
In the Eastern Pacific, Hurricane Hilary has intensified into an impressive Category 4 hurricane with 145 mph winds, and has brought 2 - 3 inches of rain to portions of the Mexican coast west of Acapulco. Hilary is headed west, away from Mexico, and the storm's rains should not cause major flooding problems for Mexico. However, a trough of low pressure expected to move over the Western U.S. early next week may be strong enough to turn Hilary to the north, and both the GFS and ECMWF models predict Hillary could hit Mexico's Baja Peninsula on Thursday. If this scenario does occur, Hilary would likely be much weaker, due to the colder waters it would have to traverse to get to Baja. It is possible that moisture from Hilary could work its way northwards into Arizona, New Mexico, and Texas late next week, bringing some drought relief. Hilary is the fourth Category 4 hurricane in the Eastern Pacific this year, and the second strongest, behind Hurricane Dora, which had 155 mph winds. The GOES-West satellite is in super rapid scan mode today for Hilary, and you can view satellite loops with images taken every minute from the NOAA/CIRA website.

Elsewhere in the tropics
In the far eastern Atlantic, a tropical wave that emerged from the coast of Africa Thursday is predicted by the GFS model to develop into a tropical depression early next week. The disturbance is currently moving west, but steering currents favor a west-northwest to northwest track early next week. NHC gave the disturbance a 10% chance of developing into a tropical depression by Sunday in their 8 am Tropical Weather Outlook.

Japan is cleaning up from Typhoon Roke, which made landfall near Japan’s Hamamatsu City in Shizuoka Prefecture at 2:00 pm local time (05:00 UTC) on September 21. Maximum sustained winds at landfall were 180 km/h [112.5 mph], making Roke a strong Category 2 storm. AIR-Worldwide is estimating that insured damages from Roke were $150 - $600 million, mostly from wind damage. The typhoon killed 12 and left 5 people missing in Japan.

Jeff Masters

Hurricane

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Ophelia temporarily strengthens

By: JeffMasters, 1:42 PM GMT on September 22, 2011

Tropical Storm Ophelia passed just south of buoy 41041 early this morning, and the sustained winds of 60 mph measured at the buoy were a bit of a surprise, given the storm's sheared appearance on satellite imagery. Ophelia is showing the classic appearance of a tropical storm experiencing high wind shear. The low level center of circulation is exposed to view, and the storm's heavy thunderstorms have been pushed to the northeast side of the center of circulation. An analysis from the University of Wisconsin CIMMS group shows a high 20 - 25 knots of wind shear due to strong upper level southwesterly winds. Water vapor satellite images show a large area of dry air to the the west of Ophelia, and the strong upper level west-southwesterly winds bringing high wind shear to the storm are also injecting dry air into the storm's core, interfering with development. Ophelia will be passing north of buoy 41040 Friday morning, and the Hurricane Hunters will be making their first flight into Ophelia on Friday morning.


Figure 1. Morning satellite image of Ophelia showing the low-level center exposed to view, with all the storm's heavy thunderstorms pushed to the northeast side.

Forecast for Ophelia
The latest SHIPS model forecast predicts that Ophelia will experience moderate to high wind shear of 10 - 25 knots over the next five days, and will move into a region with drier air. The combination of shear and dry air should keep Ophelia from strengthening, and is likely to weaken the storm. However, the models have backed off on calling for outright dissipation of Ophelia this weekend, as some were calling for in their runs yesterday. Ophelia is having some trouble disentangling itself from a band of heavy thunderstorms to its south, associated with the Intertropical Convergence Zone (ITCZ). This has likely kept the storm a little to the south of the expected track. Ophelia should begin moving more to the northwest by Friday, when the ridge of high pressure steering it westwards weakens. This should make the core of the storm miss the Northern Lesser Antilles. These islands could see some wind gusts of 30 - 40 mph and a few heavy rain squalls from Ophelia on Sunday, but the islands will be on Ophelia's weaker (dry) side, limiting the potential for adverse weather. At longer ranges, Ophelia may pass close to Bermuda as early as Wednesday, since a large cut-off low pressure system over the Eastern U.S. should turn Ophelia to the northwest and then north early next week. Ophelia may eventually be a threat to Canada, but it is too early to assess the odds of this happening.

Elsewhere in the tropics
In the Eastern Pacific, Tropical Storm Hilary is expected to intensify into a hurricane and bring heavy rains of 3 - 5 inches to coastal Mexico as the storm moves parallel to the coast, about 150 miles offshore. Hilary may turn north and affect Baja 7 - 10 days now, but it is too early to lay odds on this. In the far eastern Atlantic, a tropical wave that emerged from the coast of Africa this morning is predicted by the GFS and NOGAPS models to develop into a tropical depression early next week. Steering currents favor a west-northwest to northwest track early next week for this disturbance.


Figure 2. NASA posted a spectacular movie yesterday of the Aurora Australis taken by the International Space Station. The rippling green curtains of the aurora as the space station zooms overhead are amazing!

Jeff Masters

Hurricane

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Typhoon Roke batters Japan; Ophelia forms in the Central Atlantic

By: JeffMasters, 1:28 PM GMT on September 21, 2011

Typhoon Roke hit Japan near Hamamatsu at 14:00 JST Wednesday as a Category 1 typhoon with 80 mph winds. Roke brought sustained winds of 62 mph, gusting to 83 mph to the Tokyo airport at 5:25 pm local time, and a wind gust of 89 mph was reported at Shizuhama Airbase. Roke has dumped heavy rains of 155 mm (6.20") at Hamamatsu and 125 mm (4.86") at Tokyo. Damage due to flooding from Roke's heavy rains will likely be the main problem from Roke, as the soils over much of Japan are saturated from the passage of Tropical Storm Talas during the first week of September. Talas was a very slow moving storm, and brought extreme rainfall amounts of over six feet to some portions of Japan. Roke brought winds less than 25 mph to the damaged Fukishima-Dai-Iche nuclear plant northeast of Tokyo, and heavy rains of 189 mm (7.50") to Hirono, located 8 miles south of the plant.


Figure 1. Radar image of Typhoon Roke as it made landfall at 14:00 JST on September 21, 2011. The typhoon brought a large area of rainfall of 50 mm/hr (2"/hr) to Japan. Image credit: Japan Meteorological Agency.


Figure 2. MODIS image of Typhoon Roke taken at 3:55 UTC on Wednesday, September 21, 2011. At the time, Roke was a Category 1 storm with 80 mph winds. Image credit: NASA.

Tropical Storm Ophelia forms in the Atlantic
Tropical Storm Ophelia formed last night in the Central Atlantic from the tropical wave (Invest 98L) we've been tracking this week. Satellite imagery shows that Ophelia is suffering the classic symptoms of high wind shear, with the low level center of circulation exposed to view, and the storm's heavy thunderstorms pushed to the northeast side of the center of circulation. An analysis of wind shear from the University of Wisconsin CIMMS group shows a high 20 - 30 knots of wind shear due to strong upper level west-southwesterly winds affecting Ophelia. We don't have any ship, buoy, or hurricane hunter observations of Ophelia's winds, but an ASCAT pass from 7:27 pm EDT last night found top winds of 45 mph in the northeast quadrant of the storm. Ophelia will be passing south of buoy 41041 late tonight. Water vapor satellite images show dry air to the the west of Ophelia, and the strong upper level west-southwesterly winds bringing high wind shear to the storm are also injecting dry air into the storm's core, interfering with development.


Figure 3. Morning satellite image of Ophelia showing the low-level center exposed to view, with all the storm's heavy thunderstorms pushed to the northeast side.

Forecast for Ophelia
The latest SHIPS model forecast predicts that Ophelia will experience moderate to high wind shear of 10 - 25 knots over the next five days, and will move into a region with drier air. The combination of shear and dry air should keep Ophelia from strengthening, and could dissipate the storm, as predicted by the ECMWF and HWRF models. The Northern Lesser Antilles could see some wind gusts of 30 - 40 mph and heavy rain squalls from Ophelia on Saturday and Sunday, but right now it looks unlikely that the islands would see sustained tropical storm force winds of 39+ mph, since they are likely to be on Ophelia's weaker (dry) side. At longer ranges, Bermuda will have to keep an eye on Ophelia, since a large cut-off low pressure system over the Eastern U.S. should turn Ophelia to the northwest and then north early next week. Ophelia may eventually be a threat to Canada, but it is too early to assess the odds of this happening.

Ophelia is the 15th named storm this year, putting 2011 in 10th place for the most number of named storms in a year. Ophelia's formation date of September 21 puts 2011 in 4th place for earliest date of arrival of the season's 15th storm. Only 2005, 1936, and 1933 had an earlier 15th storm. With only three of this year's fifteen storms reaching hurricane strength, though, this year has been near average for destructive potential. Atlantic hurricane records go back to 1851.

Jeff Masters

Hurricane

Permalink

Typhoon Roke bears down on Japan; 98L continues to grow more organized

By: JeffMasters, 6:48 PM GMT on September 20, 2011

Powerful Category 3 Typhoon Roke is bearing down on Japan, and is expected to hit the main island of Honshu on Wednesday morning, local time. Roke is on a dangerous track for Japan, one that would take the storm over some of the most heavily populated areas of the country. Heavy rains from Roke have already reached the coast of Japan, as seen on Japanese radar. However, Roke is starting to weaken, as seen in latest satellite imagery. The eye is no longer apparent, the cloud tops have warmed, and a slot of dry air has gotten wrapped into the storm's northwest side. Wind shear should continue to weaken Roke as it approaches landfall; shear is currently a high 20 knots, and will increase to 30 knots by Wednesday morning. Given the current weakening trend, I expect Roke is most likely to be a Category 2 typhoon at landfall.

Typhoon's Roke's storm surge, winds, and heavy rains will all be a concern. A damaging storm surge is likely to the right of where the center makes landfall, since Roke is a large storm whose winds are spread out over a wide area. If Roke tracks farther to the east than expected, a large storm surge may affect Tokyo Bay. Perhaps the biggest concern from the storm is heavy rain. The soils over much of Japan are saturated from the passage of Tropical Storm Talas during the first week of September. Talas was a very slow moving storm, and brought extreme rainfall amounts of over six feet to some portions of Japan. Roke is expected to bring up to 20 more inches of rain along its path. Roke could bring winds of 30 - 40 mph and heavy rains of 3 - 5 inches to the damaged Fukishima-Dai-Iche nuclear plant northeast of Tokyo.


Figure 1. MODIS image of Typhoon Roke taken at 1:45 pm local time (4:45 UTC) on Tuesday, September 20, 2011. At the time, Roke was a Category 2 storm with 110 mph winds. Image credit: NASA Earth Observatory.

Invest 98L continues to grow more organized
A tropical wave midway between Africa and the Lesser Antilles (Invest 98L) has increased in organization this afternoon, but still lacks a well-defined surface circulation. Satellite imagery shows a number of curved spiral bands have formed this afternoon, and the area covered by heavy thunderstorms has steadily increased. An ASCAT pass from 8:21 am EDT this morning did not capture the full circulation of the storm, but did show winds of 30 mph on the east side of the center. Wind shear as diagnosed by the SHIPS model has increased to a moderate 10 - 15 knots, and is predicted to stay moderate through Friday. Ocean temperatures are 28 - 28.5°C, well above the threshold typically needed for a tropical storm to spin up. Water vapor satellite images show 98L is embedded in a moist environment, but there is dry air to the system's northwest. Given that the shear has now increased to the moderate level, this dry air may begin to hinder development on Wednesday. An analysis of upper level winds from the University of Wisconsin CIMMS group shows a pattern favorable for development, with an outflow channel open to both the north and south available to ventilate the storm and allow 98L to efficiently lift plenty of moisture to high levels.


Figure 2. Afternoon satellite image of 98L.

The latest 8 am EDT (12Z) runs of the computer models show either no development of 98L, or development of 98L into a tropical depression or weak tropical storm by Saturday. 98L's westward motion of 5 - 10 mph should bring the storm into the Lesser Antilles Islands by Saturday, though the models are not in strong agreement about the forward speed of the storm. The GFDL model brings 98L into the islands on Friday, while the HWRF model keeps the storm east of the islands through Sunday. If 98L takes a more west-northwesterly path through northern Lesser Antilles, which has been the preferred track for tropical systems this year, the disturbance should encounter high wind shear in excess of 20 knots due to strong upper-level winds out of the west. This shear should make it difficult for 98L to intensify as it moves though the islands. However, if 98L takes a more southerly path across Barbados, as predicted by the GFDL model, the storm will miss seeing the high shear area that lies over the northern islands, and the storm would have more opportunity to strengthen. The most likely scenario I see at this point is for 98L to be a weak tropical storm on Saturday as it moves through the Lesser Antilles--but there is more than the usual amount of uncertainty in both the track and intensity forecast. NHC gave the disturbance a 70% chance of developing into a tropical depression by Thursday in their 2 pm Tropical Weather Outlook.

September temperatures return to normal over the U.S.
The summer of 2011 was the second hottest in U.S. history, but September of 2011 is so far shaping up to be an average one for temperature. A series of cold fronts and cold-cored low pressure systems have moved southwards out of Canada this month, bringing typical amounts of cool air to the country. If you want to select dates for the start and end of the U.S. heat wave of 2011, the dates to pick would be May 20 - September 4. During the period May 20 - September 4, 2011, the number of daily record high temperatures at the 515 major airports in the U.S. exceeded the number of daily low temperature records every day but one. That's an astonishing 107 out of 108 days! Only July 15 had more record daily lows than highs during that 108-day period. I doubt one could find a similar stretch of days anytime in U.S. weather history where such a lopsided ratio of high temperature to low temperature records existed. For the 3-month summer period of June, July, and August, 2703 daily high temperature records were set, compared to 300 daily low temperature records--a ratio of 9-to-1. Not surprisingly, the summer of 2011 wound up as the hottest summer in 75 years in the U.S., and was only 0.1°F cooler than the all-time record hottest summer, during the Dust Bowl year of 1936. But so far this September, the ratio of high temperature records to low temperature records has been close to 1-to-1. There were 283 daily high temperature records set during the first sixteen days of September, and 246 low temperature records. Eight of the first sixteen days of September have seen the lows outnumber the highs, and eight have seen the highs outnumber the lows. The latest 2-week forecast from the GFS model shows a continuation of pretty normal weather over the U.S. for the rest of the month, and September temperatures will end up close to average.

Jeff Masters

Hurricane

Updated: 6:50 PM GMT on September 20, 2011

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98L organizing; September temperatures in the U.S. return to normal

By: JeffMasters, 1:29 PM GMT on September 20, 2011

A tropical wave midway between Africa and the Lesser Antilles (Invest 98L) continues to look well-organized on satellite imagery, with a modest amount of heavy thunderstorm activity and excellent spin. An ASCAT pass from 7:47 pm EDT last night showed that 98L had a moderately well-defined surface circulation. Wind shear as diagnosed by the SHIPS model is light, less than 10 knots, and is predicted to stay light to moderate through Friday. Ocean temperatures are 28 - 28.5°C, well above the threshold typically needed for a tropical storm to spin up. Water vapor satellite images show 98L is embedded in a moist environment, but there is dry air to the system's northwest. However, given the light wind shear, this dry air may not pose a hindrance to development at this time. An analysis of upper level winds from the University of Wisconsin CIMMS group shows a pattern favorable for development, with an outflow channel open to both the north and south available to ventilate the storm and allow 98L to efficiently lift plenty of moisture to high levels.


Figure 1. Morning satellite image of 98L.

The models are not very aggressive about developing 98L into a tropical storm, but most of them do show some development. NHC gave the disturbance a 70% chance of developing into a tropical depression by Thursday in their 8 am Tropical Weather Outlook. 98L's westward motion of 5 - 10 mph should bring the storm into the Lesser Antilles Islands by Saturday, though the models are not in strong agreement about the forward speed of the storm. The GFDL model brings 98L into the islands on Friday, while the NOGAPS model keeps the storm east of the islands through Tuesday. If 98L takes a more west-northwesterly path through northern Lesser Antilles, which has been the preferred track for tropical systems this year, the disturbance should encounter high wind shear in excess of 20 knots due to strong upper-level winds out of the west. This shear should make it difficult for 98L to intensify as it moves though the islands. However, if 98L takes a more southerly path across Barbados, as predicted by the GFDL model, the storm will miss seeing the high shear area that lies over the northern islands, and the storm would have more opportunity to strengthen. The most likely scenario I see at this point is for 98L to be a weak tropical storm on Saturday as it moves through the Lesser Antilles--but there is more than the usual amount of uncertainty in both the track and intensity forecast.

September temperatures return to normal over the U.S.
The summer of 2011 was the second hottest in U.S. history, but September of 2011 is so far shaping up to be an average one for temperature. A series of cold fronts and cold-cored low pressure systems have moved southwards out of Canada this month, bringing typical amounts of cool air to the country. If you want to select dates for the start and end of the U.S. heat wave of 2011, the dates to pick would be May 20 - September 4. During the period May 20 - September 4, 2011, the number of daily record high temperatures at the 515 major airports in the U.S. exceeded the number of daily low temperature records every day but one. That's an astonishing 107 out of 108 days! Only July 15 had more record daily lows than highs during that 108-day period. I doubt one could find a similar stretch of days anytime in U.S. weather history where such a lopsided ratio of high temperature to low temperature records existed. For the 3-month summer period of June, July, and August, 2703 daily high temperature records were set, compared to 300 daily low temperature records--a ratio of 9-to-1. Not surprisingly, the summer of 2011 wound up as the hottest summer in 75 years in the U.S., and was only 0.1°F cooler than the all-time record hottest summer, during the Dust Bowl year of 1936. But so far this September, the ratio of high temperature records to low temperature records has been close to 1-to-1. There were 283 daily high temperature records set during the first sixteen days of September, and 246 low temperature records. Eight of the first sixteen days of September have seen the lows outnumber the highs, and eight have seen the highs outnumber the lows. The latest 2-week forecast from the GFS model shows a continuation of pretty normal weather over the U.S. for the rest of the month, and September temperatures will end up close to average.

Jeff Masters

Hurricane

Updated: 1:39 PM GMT on September 20, 2011

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Invest 98L spinning up; outlook for remainder of hurricane season

By: JeffMasters, 2:09 PM GMT on September 19, 2011

A tropical wave midway between Africa and the Lesser Antilles (Invest 98L) continues to look well-organized on satellite imagery, with a modest amount of heavy thunderstorm activity and spin. An ASCAT pass from 8:08 pm EDT last night showed 98L was close to closing off a well-defined surface circulation. Wind shear as diagnosed by the SHIPS model is light, less than 10 knots, and is predicted to stay light to moderate through Friday. Ocean temperatures are 28 - 28.5°C, well above the threshold typically needed for a tropical storm to spin up. Water vapor satellite images show 98L is embedded in a moist environment, but there is dry air to the system's northwest. However, given the light wind shear, this dry air may not pose a hindrance to development at this time. An analysis of upper level winds from the University of Wisconsin CIMMS group shows a pattern favorable for development, with an outflow channel open to both the north and south available to ventilate the storm and allow 98L to efficiently lift plenty of moisture to high levels.


Figure 1. Morning satellite image of 98L.

The models are not very aggressive about developing 98L into a tropical depression, but most of them do show some weak development. NHC gave the disturbance a 60% chance of developing into a tropical depression by Wednesday in their 8 am Tropical Weather Outlook. Given the recent increase in spin on visible satellite images and favorable environment for development, I'd bump these odds up to 70%. 98L is currently moving little, but is expected to begin a westward motion at 10 mph today. This motion would take 98L into the Lesser Antilles Islands by Friday or Saturday. The northern Lesser Antilles would be most likely to see the core of the storm, as has been the case for all of this year's disturbances. However, a more southerly path across Barbados, as predicted by the GFS model, cannot be ruled out. Once 98L does reach the Lesser Antilles, all of the models indicate the storm will see a sharp increase in vertical wind shear due to strong upper-level winds out of the west. This shear should make it difficult for 98L to intensify as it moves though the islands.

Atlantic hurricane outlook for the rest of September
Ocean temperatures are starting to decline in the North Atlantic, though remain much above average in the Main Development Region (MDR) for hurricanes, from the coast of Africa to the coast of Central America, between 10°N and 20°N latitude. The latest departure of sea surface temperature (SST) from average plot (Figure 2) shows a large area of ocean temperatures near 1°C above average. The water temperatures were 0.8°C above average in this region during August, which is the 4th highest such reading on record. These warm waters will allow for an above-average chance of African tropical waves developing through early October. By early October, the African Monsoon typically begins to wane, spawning fewer tropical waves that tend to be weaker, and we should stop seeing development of newly-emerged tropical waves off the coast of Africa.


Figure 2. Departure of sea surface temperature (SST) from average for September 19, 2011. Ocean temperatures were about 1°C above average over much of the Main Development Region (MDR) for hurricanes, from the coast of Africa to the coast of Central America, between 10°N and 20°N latitude. In the Pacific off the coast of South America, we can see the tell-tale signature of a La Niña event, with cooler than average waters along the Equator. Also note the cooler than average waters between Bermuda and Puerto Rico, due to the passage of Hurricane Maria and Hurricane Katia. Image credit: NOAA/NESDIS.

Wind shear has been near average over the tropical Atlantic this hurricane season, and is currently at its climatological low point, which occurs in mid-September. The latest 2-week run of the GFS model shows wind shear will remain at the sort of typical low levels we usually see this time of year. With ocean temperatures at near-record warm levels, this combination would tend to favor formation of at least two tropical storms between now and the beginning of October. One inhibiting factor, though, may be the continued presence of dry, stable air over the tropical Atlantic. Hurricanes like to have an unstable atmosphere, with moist, warm air near the surface, and cold, dryer air aloft. This situation helps the updrafts in the storm grow stronger. This year, we've had unusually stable air (Figure 3.) This has really put the brakes on intensification of most of the tropical storms that have formed. The current ratio of 14 named storms but only 3 hurricanes is unprecedented in the historical record, going back to 1851. Usually, just over half of all Atlantic tropical storms intensify into hurricanes. One other factor to consider, the 30-60 day pattern of increased thunderstorm activity known as the Madden-Jullian Oscillation (MJO), looks like it will have little influence over the coming week. The MJO has been weak all month, and is predicted to stay weak for the remainder of this week.


Figure 3. Vertical instability, as measured by the difference in temperature near the surface to the bottom of the stratosphere. The atmosphere in the Caribbean (left) and tropical Atlantic between Africa and the Lesser Antilles Islands (right) has been much more stable than average this year (average is the thick black line). Image credit: NOAA/CIRA.

Forecast of the rest of hurricane season
We are past the half-way point of the Atlantic hurricane season, which typically peaks on September 10. On average, about 60% of the activity has occurred by this point in the season. Since we've already had 14 named storms and 3 hurricanes, at the current rate, we would expect to see another 8 or 9 named storms, with 1 or 2 of them reaching hurricane strength. It's pretty tough to maintain the sort of activity levels we've seen so far this year, so I am forecasting we'll see 7 more named storms during the remainder of this season, taking us all the way to "W" in the alphabet. With the unusually stable air over the Atlantic showing no signs of abating, I predict that we'll see just 2 of these storms reach hurricane strength. As far as steering currents go, the latest 2-week forecast from the GFS model doesn't show any significant changes to the jet stream pattern we've seen all summer. There will continue to be a parade of troughs of low pressure moving off the U.S. East Coast that will tend to curve any storms northwards and then northeastwards out to sea, once they penetrate north of the Lesser Antilles Islands. This pattern favors strikes on North Carolina and New England, and discourages strikes on Texas. I doubt Texas will see a tropical storm this year given this steering pattern, and considering that Texas' tropical cyclone season tends to peak in late August and early September. It is quite unusual for Texas to have a tropical storm or hurricane this late in the season, so they will probably have to look elsewhere for drought-busting rains.

Jeff Masters

Hurricane

Updated: 2:14 PM GMT on September 19, 2011

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Arctic sea ice bottoms out near all-time low; August was Earth's 4th - 8th warmest

By: JeffMasters, 6:11 PM GMT on September 17, 2011

Arctic sea ice extent hit its minimum on September 9 this year, falling to its second lowest value since satellite measurements began in 1979, according to the National Snow and Ice Data Center . More than one third (35%) of the Arctic sea ice was missing this summer, compared to the 1979 - 2000 average. This is an area about the size of the Mediterranean Sea. The 2011 sea ice minimum was very close to the all-time record low set in 2007; in fact, the University of Bremen rated the 2011 loss the greatest on record. For the fourth consecutive year, and fourth time in recorded history, ice-free navigation was possible in the Arctic along the coast of Canada (the Northwest Passage), and along the coast of Russia (the Northeast Passage.) Mariners have been attempting to sail these waters since 1497.

While the record low sea ice year of 2007 was marked by a very unusual 1-in-20 year combination of weather conditions that favored ice loss (including clearer skies, favorable wind patterns, and warm temperatures), 2011's weather patterns were much closer to average. The fact we pretty much tied the record for most sea ice loss this year despite this rather ordinary weather is a result of the fact that large amounts of thicker, multi-year ice has melted or been flushed out of the Arctic since 2007. As a result of the loss of this old, thick ice, both 2010 and now 2011 set new records for the lowest volume of sea ice in the Arctic, according the University of Washington PIOMAS model. Given the very thin ice now covering most of the Arctic, we can expect truly dramatic sea ice loss the next time 1-in-10 year or 1-in-20 year warmth and sunshine invades the Arctic. We are definitely on pace to see the Arctic virtually sea ice-free in summer by 2030, as predicted by several leading Arctic sea ice scientists. I expect we'll see more than half of the Arctic ice gone and the North Pole liquid instead of solid by the summer of 2020, and probably sooner.


Figure 1. Arctic sea ice extent in 2011 (blue line) compared to the record low year of 2007 (dashed green line) and average (thick grey line.) Image credit: National Snow and Ice Data Center .

When was the last time the Arctic was this ice-free?
We can be sure the Northwest Passage was never open for ice-free navigation--particularly ice-free navigation for multiple years in a row--between 1900 and 2000, as we have detailed ice edge records from ships (Walsh and Chapman, 2001). It is very unlikely the Passage was open between 1497 and 1900, since this spanned a cold period in the northern latitudes known as "The Little Ice Age". Ships periodically attempted the Passage and were foiled during this period, and the native Inuit people have no historical tales of the Passage being navigable at any time in the past.

The Northwest passage may have been open multiple years in a row for ice-free navigation at some period during the Medieval Warm Period, between 1000 and 1300 AD. A better candidate was the period 6,000 - 8,500 years ago, when the Earth's orbital variations brought more sunlight to the Arctic in summer than at present. Funder and Kjaer (2007) found extensive systems of wave generated beach ridges along the North Greenland coast that suggested the Arctic Ocean was ice-free in the summer for over 1,000 years during that period. Prior to that, the next likely time was during the last inter-glacial period, 120,000 years ago. Arctic temperatures then were 2 - 3°C higher than present-day temperatures, and sea levels were 4-6 meters higher.

However, it is possible that the recent summer low-ice conditions in the Arctic are unprecedented for the past 800,000 years, according to a 2011 press release by Project CLAMER, a European group dedicated to climate change and European marine ecosystem research. They found that a tiny species of plankton called Neodenticula seminae that went extinct in the North Atlantic 800,000 years ago has become a resident of the Atlantic again, having drifted from the Pacific through the Arctic Ocean thanks to dramatically reduced polar ice. The 1999 discovery represents "the first evidence of a trans-Arctic migration in modern times" related to plankton, according to the UK-based Sir Alister Hardy Foundation for Ocean Science, whose researchers warn that "such a geographical shift could transform the biodiversity and functioning of the Arctic and North Atlantic marine ecosystems."

It is possible we'll have a better idea of historical ice-free conditions in the Arctic in the next few years. A new technique that examines organic compounds left behind in Arctic sediments by diatoms that live in sea ice give hope that a detailed record of sea ice extent extending back to the end of the Ice Age 12,000 years ago may be possible (Belt et al., 2007). The researchers are studying sediments along the Northwest Passage in hopes of being able to determine when the Passage was open during the past 12,000 years.

References
Belt, S.T., G. Masse, S.J. Rowland, M. Poulin, C. Michel, and B. LeBlanc, "A novel chemical fossil of palaeo sea ice: IP25", Organic Geochemistry, Volume 38, Issue 1, January 2007, Pages 16-27.

Funder, S. and K.H. Kjaer, 2007, "A sea-ice free Arctic Ocean?", Geophys. Res. Abstr. 9 (2007), p. 07815.

Walsh, J.E and W.L.Chapman, 2001, "Twentieth-century sea ice variations from observational data", Annals of Glaciology, 33, Number 1, January 2001 , pp. 444-448.

August 2011: Earth's 4th - 8th warmest on record
August 2011 was the globe's 8th warmest August on record, according to the National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center (NCDC). NASA's Goddard Institute for Space Studies rated August the 4th warmest on record. Land temperatures during August were the 2nd warmest on record, and ocean temperatures were the 12th warmest on record. Ocean temperatures in the Atlantic Ocean's Main Development Region (MDR) for hurricanes, from the coast of Africa to the coast of Central America between 10°N and 20°N latitude, were 0.8°C above average, the 4rd warmest August on record. Global satellite-measured temperatures for the lowest 8 km of the atmosphere were the 6th or 3rd warmest in the 34-year record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH). For more details on global extremes during August, see the details from weather historian Christopher C. Burt.


Figure 2. Departure of temperature from average for August 2011. Image credit: National Climatic Data Center (NCDC).

Maria hits Newfoundland
Hurricane Maria hit Newfoundland, Canada yesterday afternoon near 3:30 pm local time as a Category 1 hurricane with 75 mph winds. However, the hurricane's strongest winds were over water, and the storm brought very little in the way of strong winds or heavy rain to the island. Cape Race at the southeast tip of Newfoundland saw sustained winds of 41 mph, gusting to 54 mph at 3:30 pm Friday as the center of the storm passed. Winds in the capital of St. John's peaked at 37 mph, gusting to 46 mph, at 10:30 am local time. Maria's strike makes this Newfoundland's second consecutive year with a hurricane strike, something that has never occurred since hurricane record keeping began in 1851. Last year, Hurricane Igor killed one person on Newfoundland, and damage exceeded $100 million, making Igor the most damaging tropical cyclone in Newfoundland history.


Figure 3. Satellite image of Hurricane Maria taken at 12:15 pm EDT September 16, 2011. At the time, Maria was a Category 1 hurricane with 75 mph winds. Image credit: NOAA Environmental Visualization Lab.

Invest 97L
For the first day since August 18, we don't have a named storm in the Atlantic. However, we have a new area to watch. A tropical wave that moved off the coast of Africa Friday and is now 300 miles south of the Cape Verde Islands is moving west at 10 - 15 mph. The wave has developed a modest amount of heavy thunderstorm activity and spin, and has been designated Invest 97L by NHC. Wind shear as diagnosed by the SHIPS model is light, 5 - 10 knots, and is predicted to stay light to moderate through Tuesday morning. Ocean temperatures are 27.5°C, one degree above the threshold typically needed for a tropical storm to spin up. Water vapor satellite images show 97L is embedded in a moist environment.

Most of the models develop 97L into a tropical depression by Tuesday; NHC gave the disturbance a 20% chance of developing into a tropical depression by Monday in their 2 pm Tropical Weather Outlook. 97L should head west or west-northwest towards the Lesser Antilles over the next six days, and could arrive in the islands as early as Friday--though most of the models predict a later arrival. It is likely 97L will encounter the usual troubles storms this year have had with wind shear and dry air on the long trek across the Atlantic.

I'll have a new post on Monday, when I'll discuss the long-range hurricane outlook for the rest of September.

Jeff Masters

Climate Change Climate Summaries Sea Ice Hurricane

Updated: 11:26 AM GMT on September 19, 2011

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Hurricane Maria rushes towards Newfoundland

By: JeffMasters, 1:41 PM GMT on September 16, 2011

Hurricane Maria is bearing down on Newfoundland, Canada, as a Category 1 hurricane with 80 mph winds. The wind shear over Maria turned out to be much lower than was predicted yesterday, allowing the storm to organize into the season's third hurricane. Latest satellite imagery shows that Maria is steadily degrading, with a hole in the storm's southwest eyewall, and the cloud pattern distorted by 30 - 50 knots of wind shear. The eyewall has collapsed, as seen on recent microwave satellite imagery. Maria's very fast forward speed of 45 mph means that only locations on the right (strong) side will experience hurricane force winds. With the center of Maria expected to pass over the extreme southeast tip of Newfoundland, only a small region of the island near Cape Race will see the powerful right-front quadrant of the storm. Winds at Sagona Island on the south shore of Newfoundland were sustained at 50 mph at 7:30 am local time, but have dropped to 37 mph at 9:10 am. Winds in the capital of St. John's have been rising steadily this morning, and were sustained at 37 mph, gusting to 46 mph, at 10:30 am local time. Winds will probably reach sustained speeds of 55 - 65 mph between 1 pm and 5 pm today in St. Johns, causing considerable tree damage and power failures. Radar out of Newfoundland shows the hurricane has been dumping heavy rains over the southeastern portion of the island this morning; rainfall has been under a half inch thus far at most locations, though. Along with wind damage, heavy rains leading to flash flooding are the main threat from Maria; last year, heavy rains of up to 8 inches from Hurricane Igor caused major damage in Newfoundland. Fortunately, Maria's rains are not expected to be as heavy as Igor's. According to the Canadian Hurricane Center, rivers in eastern Newfoundland are currently at average to below average levels, which will limit the amount of flooding. Maria's storm surge will arrive when the normal astronomical tide will be going out, limiting the damage the expected 3-foot storm surge will do.

Yesterday, Maria brought a brief 8-minute period of sustained winds of tropical storm force, 39 mph, to the Bermuda airport. Bermuda picked up 0.20" of rain from Maria.


Figure 1. Radar image of Tropical Storm Maria taken at 10:13 am EDT September 15, 2011. Image credit: Bermuda Weather Service.

Newfoundland's second consecutive year with a hurricane
If Maria strikes Newfoundland as a hurricane, this will be the province's second consecutive year with a hurricane strike, something that has never occurred since hurricane record keeping began in 1851. Last year, Hurricane Igor killed one person on Newfoundland, and damage exceeded $100 million, making Igor the most damaging tropical cyclone in Newfoundland history. A summary of the impact of Igor prepared by Environment Canada put 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 2. 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.

Elsewhere in the tropics
All of the models have been sporadically predicting development of a tropical wave 5 - 7 days from now between Africa and the Lesser Antilles. The location and timing of the hypothetical storm have been inconsistent, and there is at present no signs of anything brewing. The NOGAPS model continues to predict a strong tropical disturbance or tropical depression could form in the Caribbean 6 - 7 days from now, near Jamaica. None of the other models is supporting this idea, so the NOGAPS model is probably wrong on this scenario. I'll have an update Saturday afternoon.

Jeff Masters

Hurricane

Updated: 1:46 PM GMT on September 16, 2011

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Maria brushes Bermuda; 24-hour blitz by Climate Reality Project underway

By: JeffMasters, 2:27 PM GMT on September 15, 2011

Tropical Storm Maria is roaring past Bermuda, bringing winds near tropical storm force. At 11 am local time, winds at the Bermuda airport were sustained at 36 mph, just below the 39 mph threshold of tropical storm strength. Outer spiral bands of Maria have brought a few brief heavy rain squalls to the island, as seen on Bermuda radar. The core of Maria is now at its closest point of approach to the island, about 150 miles (240 km) to the west, and the island may yet see an hour of two of sustained winds of 40 - 45 mph. Maria is headed north-northeast, and will brush Newfoundland, Canada on Friday afternoon. Since Newfoundland will be on the weak (left) side of a rapidly weakening Maria, I'm not expecting much in the way of wind damage from the storm in Canada, though heavy rains may cause isolated minor to moderate flooding. Top sustained winds in St. Johns will probably be in the 25 - 35 mph range Friday afternoon, though a few hours of tropical storm force winds of 40 - 45 mph are possible if Maria ends up tracking farther west than expected.


Figure 1. Radar image of Tropical Storm Maria taken at 10:13 am EDT September 15, 2011. Image credit: Bermuda Weather Service.

Elsewhere in the tropics
Even the busiest of hurricane seasons have lulls, and we're hitting one this week during what is traditionally the busiest week of hurricane season. A westward-moving tropical wave a few hundred miles south of the Cape Verde Islands, off the coast of Africa, has a modest amount of poorly organized heavy thunderstorm activity. This wave is under a moderate 10 - 20 knots of wind shear, is in a moist environment, and is over warm waters, so has the potential for some development, though NHC is currently not mentioning it in their Tropical Weather Outlook. The UKMET and NOGAPS models predict this wave could develop into a tropical depression 5 - 6 days from now. The NOGAPS model continues to predict the Western Caribbean off the coast of Nicaragua could see the development of a tropical depression 6 - 7 days from now, but the other models are showing little support for this scenario.


Figure 2. Heidi Cullen of Climate Central introduces Boulder, Colorado teacher John Zavalney, one of the presenters of the Climate Reality Project's 24-hour live streaming special.

The Climate Reality Project
The Climate Reality Project (climaterealityproject.org) is a little more than halfway through their live, 24-hour streaming video effort that features 24 different presenters for 24 hours, representing every time zone around the globe. The presentations began last night at 7 pm EDT, and will end tonight at 7 pm EDT. It's worth checking out; there have been some interesting presentations and some dull ones. Interspersed with the presentations are panel discussions with some slick Google Earth graphics; last night's discussions were led by Heidi Cullen of Climate Central, who is a rarity--a very personable and well-spoken scientist, and someone you'll be seeing on TV much more in coming years. The Climate Reality Project showed one excellent video tracking the history of industry-funded denial of science that began with the tobacco industry, something I've discussed as well in post called The Manufactured Doubt Industry and the hacked email controversy. Also shown were two cute 15 - 30 second comedy videos. But while the Climate Reality Project's 24-hour blitz has already gotten 3 million people to tune in, its documentary-style tone and Powerpoint lectures will not be engaging enough to keep most visitors around for more than a few minutes. Ph.D. oceanographer Randy Olson, who left a tenure-track professorship to become a Hollywood film maker, has written an excellent book called Don't be Such a Scientist, about the failure of scientists to communicate in way that will engage people (I thought so highly of the book that I bought 20 copies of the book to give away to students at the University of Michigan's Department of Atmospheric Science this year.) In the latest post in his blog, The Benshi, Olson outlines how the climate community has failed in the main way needed to engage an audience: create a likable voice through the effective telling of stories, which is a less literal means of communication and is less cerebral and thus reaches a mass audience. Future efforts at communication by the climate science community really need to work on using the telling of stories by likable voices in order to get their message across, and I highly recommend that all climate scientists who do public outreach read Olson's book "Don't be Such a Scientist."

Jeff Masters

Climate Change Hurricane

Updated: 8:47 PM GMT on September 15, 2011

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New floods in Pakistan kill 226; Maria heads towards brush with Bermuda

By: JeffMasters, 1:53 PM GMT on September 14, 2011

A year after enduring the most devastating flooding in its history, Pakistan is again experiencing historic floods. An unusually heavy and late-lasting monsoon has brought torrential rains to Pakistan's southeast Sindh Province, which borders India to the east and the Arabian Sea to the south, and includes Pakistan's largest city, Karachi. The heavy rains began in the 2nd week of August, and have continued into the 2nd week of September, accumulating to 2 1/2 times more than average. According to Dr. Qamar-uz-Zaman Chaudhry, Pakistan's Federal Advisor on Climate Affairs, this is the highest 4-week monsoon rainfall total ever recorded in Sindh province, amounting to more than 37 million acre feet of water, "which is unimaginable." The "unimaginable" rains occurred after a 12-month period where the province received no rain and was under severe drought conditions. At least 226 people have been killed in the new flooding, 1.2 million houses have been damaged or destroyed, and 280,000 people made homeless. There were already 1 million people needing food aid and 800,000 families without permanent shelter due to last year's floods, making this year's renewed flooding particularly disruptive. According to the India Meteorological Department, by September 1, the monsoon usually begins to retreat from northwest India and southeastern Pakistan. That hasn't happened this year, and the monsoon rains are forecast to continue at least for the remainder of this week--well into the 3rd week of September. This very unusual monsoon season also started a week earlier than normal.


Figure 1. Rainfall during the 2011 monsoon season has accumulated to 8 to 12 inches above average over portions of Pakistan's Sindh Province. Image credit: Pakistan Meteorological Department. Before and after satellite images of the flood are available at NASA Earth Observatory.

Is there a climate change connection?
Last year, heavy monsoon rains were enhanced by a very unusual jet stream configuration that brought cool air and rain-bearing low pressure systems to northern Pakistan. The great floods of 2011--rightfully called Pakistan's Katrina--submerged one fifth of the country, killing 1985 people, leaving 11 million homeless, and doing a record $9.5 billion in damage. This year, the monsoon weather patterns were much different, but also highly unusual, resulting in yet another great flood in Pakistan. In an interview with dawn.com, Dr. Qamar-uz-Zaman Chaudhry, Pakistan's Federal Advisor on Climate Affairs, stated: "...climate change has become a reality for Pakistan. Clearly, Pakistan is heading for an increased frequency and intensity of extreme weather events which included frequent floods and droughts, and the need of the hour is to plan for the future changes." These events are in line with international climate change projections, he said.


Figure 2. Evacuations in Pakistan's Sindh Province during the summer 2011 floods. Image credit: Pakistan Meteorological Department.

A skeptic of Dr. Qamar's arguments might point to the fact that monsoon rainfall in neighboring India was not all that unusual in either 2010 or 2011, and that major monsoon flooding disasters in back-to-back years in Pakistan were probably just bad luck. However, the monsoon in India and Pakistan has undeniably changed in recent decades. In a study published in Science in 2006, Goswami et al. found that the level of heavy rainfall activity in the monsoon over India had more than doubled in the 50 years since the 1950s, leading to an increased disaster potential from heavy flooding. Moderate and weak rain events decreased over the past 50 years, leaving the total amount of rain deposited by the monsoon roughly constant. The authors commented, "These findings are in tune with model projections and some observations that indicate an increase in heavy rain events and a decrease in weak events under global warming scenarios." A warming climate loads the dice in favor of heavier extreme precipitation events. This occurs because more water vapor can evaporate into a warmer atmosphere, increasing the chances of record heavy downpours. In addition, heavy downpours preferentially occur during thunderstorms, and a warmer climate produces a longer period of time during the year when thunderstorms can occur, giving more opportunities for heavy rainfall events. During August 2011, ocean temperatures in the Arabian Sea off the coast of Pakistan, in the region between 15°N - 25°N, 60°E - 70°E, were 0.8°C (1.4°F) above average, according to an analysis I did of the HADSST2 dataset. This was the 5th highest such value in over 100 years of record keeping. During the July 2010 monsoon, this region of ocean was 1.1°C (2.0°F) above average, the warmest July ocean temperatures on record. The extra heat in the ocean the past two summers have undoubtedly contributed to the high rainfall totals in Pakistan by allowing more water vapor to evaporate into the air. Thus, we should expect to see an increased number of disastrous monsoon floods in coming decades as the climate continues to warm and the oceans off the coasts of India and Pakistan heat up. Since the population continues to increase at a rapid rate in the region, death tolls from monsoon flooding disasters are likely to climb dramatically in coming decades. Another concern is that climate change might lead to more failures of the monsoon--years when the rains are far below normal, leading to widespread drought and crop failures. This is a more dangerous scenario, since historically, droughts have been much more deadly than floods in Asia. Failure of the monsoon rains typically occur during El Niño years, so if climate change increases the frequency of El Niño, we might see an increase in the failure of the monsoon rains. So far, climate models are unclear on how climate change might affect El Niño, so we don't know how great a concern future failures of the monsoon might be.

References
Goswami, et al., 2006, " Increasing Trend of Extreme Rain Events Over India in a Warming Environment", Science, 1 December 2006:Vol. 314. no. 5804, pp. 1442 - 1445 DOI: 10.1126/science.1132027

Tropical Storm Maria headed towards a brush with Bermuda
Tropical Storm Maria is finally pulling away from Puerto Rico, and is headed north-northwest towards a brush with Bermuda, which will occur Thursday morning. Wind shear has fallen about 5 knots since yesterday, and is now a moderate 10 - 15 knots. This reduction in shear has allowed Maria a strengthen some, and satellite loops show the storm has more heavy thunderstorms that are better organized. The storm's surface circulation is still exposed on the storm's west side, though, and Maria does not have anything close to a complete eyewall built. Maria passed near NOAA buoy 41046 this morning, which reported a 1-hour period of sustained winds of 38 mph, gusting to 45 mph. An outer spiral band of Maria is just beginning to appear on Bermuda radar.


Figure 3. Morning satellite image of Tropical Storm Maria.

Forecast for Maria
A trough of low pressure moving off the U.S. East Coast a predicted to turn Maria to the north-northeast by early Thursday, and accelerate the storm past Bermuda. The trough will also bring high wind shear of 20 - 30 knots beginning late tonight, which gives Maria just a short window of opportunity to intensify today. NHC gave Maria a 32% chance of reaching hurricane strength by Thursday in their 5 am EDT wind probability forecast. Intensification will be hampered by the fact that Maria will be passing over the cold water wake left by Hurricane Katia today. On Thursday morning, Maria will be making its closest approach to Bermuda. Bermuda will see an 8-hour period of sustained winds in the 25 - 35 mph range, accompanied by heavy rain squalls, beginning near 4 am local time on Thursday. Bermuda may experience a few hours where the wind rises above tropical storm force, 39 mph, near 8 am local time Thursday. Occasional rain squalls are expected to bring 1 - 3 inches of rain to the islands. Most of the models show that Maria will brush or strike Newfoundland, Canada on Friday afternoon. Most of the storm's high winds will be on the right side, and Maria will be weakening rapidly then, so I'm not expecting the storm will do much wind damage. Heavy rains could bring minor to moderate flooding to the eastern portion of the island.

Elsewhere in the tropics
Even the busiest of hurricane seasons have lulls, and we're hitting one this week during what is traditionally the busiest week of hurricane season. The models are backing off this morning on the development of a tropical depression or strong tropical disturbance late this week off the coast of Africa. The NOGAPS model continues to predict the Western Caribbean could see the development of a tropical depression 6 -7 days from now, but the other models are showing little support for this idea.

The Climate Reality Project
Those of you who like Al Gore's efforts to promote climate change awareness and solutions may be interested in checking out his latest effort tonight at 7 pm local time, in all 24 of the world's time zones, via climaterealityproject.org. It's a live streaming multimedia presentation created by Al Gore and delivered once per hour by 24 different presenters for 24 hours, representing every time zone around the globe.

Jeff Masters

Climate Change Flood Hurricane

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Little change to Maria; Extratropical Storm Katia batters the U.K.

By: JeffMasters, 12:31 PM GMT on September 13, 2011

There's not much new to report this morning regarding Tropical Storm Maria. Maria continues to creep slowly to the northwest, and continues to struggle with moderate wind shear of 15 - 20 knots that is preventing the storm from organizing. Satellite loops reveal a shapeless mass of heavy thunderstorms that don't much resemble a tropical cyclone. Long-range radar out of Puerto Rico does show a few respectable low-level spiral bands, and these bands have brought heavy flooding rains to the island this morning. Radar-estimated rainfall amounts over eight inches have occurred over portions of southern Puerto Rico, and flash flood warnings are posted for the La Plata River.


Figure 1. Morning radar image of Tropical Storm Maria from the Puerto Rico radar.

The trough of low pressure that is bringing hostile wind shear to Maria is predicted to weaken slightly on Wednesday, which may allow the storm to grow to Category 1 hurricane strength. Intensification will be hampered by the fact that Maria will be passing over the cold water wake left by Hurricane Katia, though. NHC is giving Maria a 24% chance of reaching hurricane strength in their 5 am EDT wind probability forecast. On Thursday, Maria will be making its closest approach to Bermuda. Bermuda will see an 8-hour period of sustained winds in the 25 - 35 mph range, accompanied by heavy rain squalls, beginning near 2 am local time on Thursday. Most of the models show that Maria will brush or strike Newfoundland, Canada on Friday afternoon. Heavy rains will be a flooding threat to the west of where Maria passes, and tree damage and power failures from high winds of 45 - 55 mph will be a concern to the east of where the center goes.


Video 1. Video of what Extratropical Storm Katia's winds were like at Malin Head, Ireland, at 1:45 pm September 12, 2011. Wind gusts reached 75 mph on Malin Head during the storm.

Extratropical Storm Katia batters the U.K.
The extratropical version of Hurricane Katia roared over northern Scotland in the U.K. yesterday, bringing hurricane-force winds gusts and heavy rains to much of the British Isles. Glen Ogle, Scotland, at an elevation of 1500 feet (546 meters), received sustained winds of 60 mph, gusting to 86 mph, at 1900 local time. Cairngorm, in the Scottish Highlands at an elevation of 4085 feet, reported sustained winds of 67 mph at 6:50 pm local time. With the trees in full leaf, tree damage was much higher than a winter or springtime storm of similar ferocity would have caused. One person was killed by a falling tree, and heavy tree damage and numerous power failures were reported throughout Britain. Other gusts experienced in Britain included 76 mph at Edinburgh Blackford Hill, 75 mph at Capel Curig in Wales, 72 mph at Glasgow Bishopton, and 71 mph at Loftus, North Yorkshire.

Wunderground's weather historian, Christopher C. Burt, says that Cairngorm summit holds the U.K. record for highest wind gust, with 172 mph measured on March 20, 1986. The record wind gust at a low-level site is 141 mph at Kinnaird's Head Lighthouse, Scotland, on February 13, 1989. Damage on the Isle of Skye during this storm was such that wind speeds in excess of 150 mph were estimated.

Elsewhere in the tropics
Several of the models predict the development of a tropical depression or strong tropical disturbance 4 - 5 days from now off the coast of Africa. The NOGAPS and GFS models are predicting the Western Caribbean could see the development of a tropical depression 7 - 8 days from now, as moisture from the Eastern Pacific flows northeast into the Caribbean.

Jeff Masters

Hurricane

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Maria pulling away from the Antillies; Ex-Katia pounding the U.K.

By: JeffMasters, 2:04 PM GMT on September 12, 2011

Tropical Storm Maria continues to struggle with moderate wind shear of 15 - 20 knots that is preventing the storm from organizing. The center of circulation lies fully exposed to view this morning, with satellite loops showing that all of Maria's heavy thunderstorms lie to the east of Maria's center. Spiral bands from Maria are bringing heavy rains to the Virgin Islands and northern Lesser Antilles, as seen on long-range radar out of Puerto Rico and Martinique radar. Radar-estimated rainfall amounts of three inches have occurred in the Virgin Islands; 0.94" has fallen in St. Thomas, which experienced a wind gust of 39 mph at 9:14 am local time.

Maria's center has been tracking more to the west than the forecast has been calling for, but since the center is so far from the heaviest thunderstorms, I wouldn't be surprised to see the center reform more to the east or east-northeast later today. The models are in unanimous agreement that Maria should resume a more northwesterly motion later today, and turn to the north by Tuesday. The trough of low pressure that is bringing hostile wind shear to Maria is predicted to slowly weaken over the next few days, which may allow the storm to grow to Category 1 hurricane strength by Wednesday. Intensification will be hampered by the fact that Maria will be passing over the cold water wake left by Hurricane Katia, though. On Wednesday, Maria will be making its closest approach to Bermuda. If Maria does manage to organize into a hurricane, Bermuda could see an 8-hour period of sustained winds of 35 - 40 mph beginning near 2 pm local time on Wednesday. Most of the models show that Maria will brush or strike Newfoundland, Canada on Friday morning. Heavy rains will be a flooding threat to the west of where Maria passes, and wind damage from high winds of 50 - 60 mph will be a concern to the east of where the center goes.


Figure 1. Morning satellite image of Tropical Storm Maria.

Extratropical Storm Katia pounding Britain
Hurricane Katia brushed by Newfoundland, Canada on Saturday, and made the transition from a tropical system to a powerful extratropical storm. Extratropical Storm Katia maintained strong winds of 50 - 65 mph as it crossed the Atlantic, and is now lashing the northern British Isles with high winds and heavy rain. At 1 pm local time, the center of ex-Katia was over northern Scotland, and Malin Head, Ireland on the north coast of Ireland, was experiencing sustained winds of 49 mph. Winds in western Scotland were also high, with Aonach Mor recording sustained winds of 51 mph at 12:50 pm local time. The UK Met Office is warning that wind gusts up to 80 mph can be expected in Scotland today, as well as flooding rains of 2 - 4 inches. Ex-Katia's strong winds will likely cause significant tree damage and power failures across Northern Ireland and Scotland today.


Figure 2. Surface wind estimate from the Windsat satellite at 4:04 am EDT on Monday, September 12, 2011. The center of Extratropical Storm Katia is marked by an "L", and winds in excess of 50 knots (58 mph, purple triangles) were occurring to the southwest of the center, near the west coast of Ireland. Image credit: NOAA.

Britain's hurricane history
Hurricanes that transition to powerful extratropical storms hit the British Isles several times per decade, on average. In September 2006, two major hurricanes named Gordon and Helene transitioned to strong extratropical storms that hit the British Isles. Only once since accurate records began in 1851 has an actual hurricane with full tropical characteristics hit Europe. This happened on September 16, 1961, when Category 1 Hurricane Debbie hit northwestern Ireland. Wind gusts reached 106 mph at Ballykelly and 104 mph at Tiree and Snaefill, and coastal radio stations reported the airwaves were jammed with calls for help from small ships and fishing craft. Eleven people were killed and 50 injured in the storm. The only other tropical cyclone recorded to have hit Europe since 1851 was Hurricane Vince of 2005, which hit southern Spain as a tropical depression on October 11, 2005. Historical documents also suggest a hurricane hit Spain on October 29, 1842.

As reported by UK Met Office forecaster John Hammond in a post on the BBC 23 degrees blog, Britain has been affected at least eight times in the past twenty years by extratropical storms that were once tropical storms or hurricanes. The most recent one was Hurricane Bill of 2009, which hit Ireland on August 25 with sustained winds of 45 mph. Bill was a Category 4 hurricane northeast of the Lesser Antilles five days prior. In 2006, a record three extratropical storms that had once been tropical cyclones hit Britain:

Extratropical Storm Alberto, which had been a strong tropical storm that hit the Florida Panhandle, hit northern Ireland and Scotland as an extratropical storm with 35 mph winds.

Extratropical Storm Gordon hit Ireland on September 21, 2006, with sustained winds of 65 mph. Gordon brought record warm temperatures as tropical air pushed north across the UK, and also strong winds that brought down power lines in Northern Ireland. Wind gusts to 60 mph (97 km/h) occurred in the Isles of Scilly off the southwest coast, and 81 mph (130 km/h) on the mainland.

Extratropical Storm Helene hit Northwestern Ireland on September 27, 2006, with sustained winds of 45 mph.


Figure 3. Path of Hurricane Lili of 1996, which caused $420 million in damage to the U.K. as an extratropical storm.

Other post-tropical cyclones that have the U.K. in the past twenty years include Hurricanes Isaac and Leslie of 2000, Hurricane Karl of 1998, and Hurricane Lili of 1996. The most severe of these storms was Extratropical Storm Lili, which hit Ireland on October 28, 1996, with sustained winds of 65 mph. Lili caused $420 million in damage (2011 dollars) in the U.K. According to Wikipedia, Lili produced a 92 mph (148 km/h) gust at Swansea, South Wales, while bringing a four ft (1.20 m) storm surge that inundated the River Thames. In Somerset, 500 holiday cottages were severely damaged. A United States oil drilling platform, under tow in the North Sea, broke loose during the storm and nearly ran aground at Peterhead. On the Isle of Wight, a sailing boat was beached at Chale Bay; luckily all five occupants were rescued. It was the most damaging storm to have struck the United Kingdom since the Great Storm of 1987, which killed 22 and did $660 million in damage (1996 dollars.) However, Lili also broke a four-month drought over southwest England.

Elsewhere in the tropics
Several of the models predict the development of a tropical depression or strong tropical disturbance 4 - 5 days from now off the coast of Africa. The NOGAPS model is predicting the Western Caribbean could see the development of a strong tropical disturbance 6 - 7 days from now.

I'll have an update Tuesday morning.

Jeff Masters

Hurricane

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Nate makes landfall; Maria organizing, but pulling away from the islands

By: JeffMasters, 4:15 PM GMT on September 11, 2011

Tropical Storm Nate made landfall at 11 am EDT this morning just north of Barra de Nautla in the Mexican state of Veracruz, as a tropical storm with 45 mph winds. Satellite loops show that there is very little heavy thunderstorm activity associated with Nate, and the storm should not cause significant flooding or damage as it pushes inland and dissipates later today.


Figure 1. Visible satellite image of Nate as it made landfall in the Veracruz state of Mexico near 11 am EDT Sunday, September 11, 2011.

Tropical Storm Maria
Tropical Storm Maria has managed to organize in the face of the persistent moderate wind shear that has affected it, and now looks a little more like a tropical storm should. Though the center of circulation lies partially exposed to view, satellite imagery shows a large area of heavy thunderstorms lies to the northeast of Maria's center. These rains and the storm's strongest winds lie well away from the Lesser Antilles Islands, though one spiral band is bringing heavy rains to the islands, as seen on Martinique radar. A wind gust of 40 mph was reported on St. Martin at 11 am EDT, and one of 36 mph affected St. Kitts and Nevis at 9 am EDT during a rain squall. The trough of low pressure that is bringing hostile wind shear to Maria is predicted to slowly weaken over the next few days, which should allow the storm to grow to hurricane strength by Tuesday. On Wednesday, Maria will be making its closest approach to Bermuda, and the island could see sustained winds in the 20 - 40 mph range. Most of the models show that Maria will brush or strike Newfoundland, Canada on Friday or Saturday, and residents there should anticipate the possibility of tropical storm conditions late this week.


Figure 2. Morning satellite image of Tropical Storm Maria.

Extratropical Storm Katia
Hurricane Katia brushed by Newfoundland, Canada yesterday morning, and is now racing east-northeast at 50 - 60 mph across the open Atlantic. On Monday, the storm will pass very close to the northern British Isles, bringing winds of 50 - 60 mph to the offshore waters of Northern Ireland and Western Scotland. Ex-Katia will bring 2 - 4 inches of rain to the coast, and its strong winds will likely cause significant tree damage and power failures.


Figure 3. The center of Extratropical Storm Katia is predicted to pass just north of the British Isles on Monday, bringing a large area 45 - 50 knots (52 - 58 mph, red colors) to the coast. This wind forecast is from the 00Z (8 pm EDT) run of the GFS model made last night. To convert from knots to mph, multiply by 1.15.

Elsewhere in the tropics
Most of the models predict the development of a tropical depression or strong tropical disturbance 5 - 6 days from now off the coast of Africa.

I'll have an update Monday morning. Peace to all this September 11!

Jeff Masters

Hurricane

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No change to Nate; Maria fizzles; Katia headed to Britain

By: JeffMasters, 3:47 PM GMT on September 10, 2011

Tropical Storm Nate in Mexico's Bay of Campeche continues to have trouble intensifying. Latest visible satellite loops show that Nate has a large, cloud-filled center, and the storm is probably pulling in dry air to its north into its center. Nate is also likely having trouble with all the cool waters it has stirred to the surface. Assuming Nate is able to close off its center from the dry air, it would take the storm at least a day to tighten up its rather large center, form a solid eyewall, and reach hurricane intensity. Nate doesn't have enough time before landfall for that to happen, and it is unlikely Nate will ever become a hurricane. The latest wind probability forecast form NHC gives Nate a 13% chance of reaching hurricane strength on Sunday. Latest radar imagery from Alvarado, Mexico shows heavy rains from Nate are affecting the coast near Veracruz, and heavy rains of 4 - 6 inches will be the main threat from Nate.


Figure 1. True-color MODIS image of Tropical Storm Nate taken at 12:45 pm EDT Friday, September 9, 2011. At the time, Nate was a tropical storm with 50 mph winds. Image credit: NASA.

Nate is a small storm, and is not likely to bring significant rains to Texas; only extreme South Texas near Brownsville could see an inch or so of rain on Sunday from an outer spiral band of Nate. Our latest wundermap wind forecast map from the European Center model, with the fire layer turned on, shows that Nate's wind field on Saturday and Sunday will not be large enough to fan the fires burning in Texas.

Tropical Storm Maria
Tropical Storm Maria doesn't look much like a tropical storm--on the latest satellite imagery it looks like a squashed question mark instead of a spiral. The surface circulation center is very poorly defined, and moderate wind shear of 15 - 20 knots has really done the Lesser Antilles Islands a big favor by ripping up Maria. It is doubtful this storm will generate any sustained winds of tropical storm force in the islands, and it is a 50/50 proposition that Maria will degenerate into a tropical disturbance and become ex-Tropical Storm Maria later today. Martinique radar shows heavy rains from Maria are mostly east of the islands, and the thunderstorms are not well-organized into spiral bands. The wind shear affecting Maria will probably last through Sunday. By Monday, wind shear is predicted to fall enough so that Maria could potentially organize again. However, the storm is expected to be far from land when that occurs. Bermuda could see a few rain showers from Maria on Wednesday, and Maria may be a threat to southeast Newfoundland late next week.


Figure 2. Morning satellite image of Tropical Storm Maria shows the the storm looks like a squashed question mark?

Hurricane Katia
Hurricane Katia brushed by Newfoundland, Canada this morning, and is now racing east-northeast at 52 mph into the open Atlantic. With water temperatures 19°C (66°F) underneath it, Katia has lost its tropical characteristics, and has transitioned to a powerful extratropical storm. Extratropical Storm Katia will continue east-northeastward towards Europe, and on Monday, the storm will pass very close to northern British Isles. The offshore waters of Northern Ireland and Western Scotland can expect storm-force winds of 50 - 60 mph on Monday as Katia roars past to the north. The storm will bring 2 - 4 inches of rain to the coast, and likely cause significant tree damage and power failures.


Figure 3. Image of Hurricane Katia taken from the International Space Station at 15 GMT September 9, 2011, by astronaut Ron Garan. At the time, Katia was a Category 1 hurricane with 85 mph winds. Long Island, New York is visible at the lower left.

Elsewhere in the tropics
The NOGAPS and UKMET models predict the possible development of a tropical wave 6 - 7 days from now off the coast of Africa.

I'll have an update by early Sunday afternoon.

Jeff Masters

Hurricane

Permalink

Little change in strength for Nate and Maria

By: JeffMasters, 8:49 PM GMT on September 09, 2011

This afternoon's observations from an Air Force Reserve hurricane hunter aircraft show that Tropical Storm Nate in Mexico's Bay of Campeche has changed little this afternoon. The 4:10 pm EDT center fix found Nate's central pressure remaining near-steady at 998 mb, and winds were near 50 mph at the surface. Latest visible satellite loops show that Nate is having trouble with the dry air to its north, which is getting wrapped into the circulation and interfering with intensification, and the intensity of Nate's thunderstorms has decreased since early this morning. Since the storm is nearly stationary, it is upwelling cooler waters from the depths that are also slowing intensification.

Wind shear remains low, near 5 knots, so once Nate manages to wall off the dry air to its north, steady intensification should occur. The 5 pm EDT NHC wind probability forecast gives Nate a 42% chance of being a Category 1 hurricane on Sunday, and 6% chance of being Category 2 or stronger. Nate probably has time to intensify to a strong Category 1 hurricane before making landfall Sunday. The main hazard to Mexico will be very heavy rains that will cause flash flooding and mudslides. The computer models continue to agree that a ridge of high pressure will build in to the north of Nate over the next few days, forcing the storm westward or southwestward to a landfall in Mexico between Tuxpam de Rodriguez Cano and Veracruz. Nate is too far south to be turned northwards towards Louisiana, as some model runs were suggesting yesterday.


Figure 1. True-color MODIS image of Tropical Storm Nate taken at 12:45 pm EDT Friday, September 9, 2011. At the time, Nate was a tropical storm with 50 mph winds. Image credit: NASA.

Nate is a small storm, and is not likely to bring significant rains to Texas; only extreme South Texas near Brownsville could see an inch or so of rain over the weekend from an outer spiral band of Nate. Our latest wundermap wind forecast map from the European Center model, with the fire layer turned on, shows that Nate's wind field on Saturday and Sunday will not be large enough to fan the fires burning in Texas.


Figure 2. Water temperatures at buoy 42055 in the Bay of Campeche, about 150 miles northwest of the center of Nate, have declined steadily over the past few days due to the mixing action from Nate's winds. Image credit: National Data Buoy Center.

Tropical Storm Maria
Tropical Storm Maria is not changing much in intensity it bears down on the Lesser Antilles Islands. We haven't had a hurricane hunter aircraft in the storm since this morning, but satellite intensity estimates are unchanged from this morning, and support classifying Maria as a tropical storm with 45 - 50 mph winds. Satellite loops show that Maria's heavy thunderstorms decreased in areal coverage and intensity since this morning, but the cloud pattern is more organized now. Maria is slowly developing spiral bands in all quadrants, and the storm has an obvious spin to it that was not apparent earlier in its life. Wind shear has fallen to the low range, 5 - 10 knots, and Maria is taking advantage of the lower shear and getting more organized. Martinique radar shows heavy rains from Maria are now affecting the islands, and the pattern has more rotation to it than it did this morning. The thunderstorms are not yet well-organized into spiral bands, though.

The intensity forecast models predict steady strengthening for Maria, and I think likely that Maria will be a tropical storm with 45 - 55 mph winds in the Northern Lesser Antilles, Virgin Islands, and Puerto Rico, and develop into a Category 1 hurricane shortly after pulling away from Puerto Rico on Sunday morning. Assuming that the Virgin Islands and Puerto Rico stay on the weaker left side of the storm, winds in those islands should be at least 15 mph less than the peak winds of the storm--so, in the 30 - 40 mph range. Islands on the right side of the storm, such as Anguilla and Barbuda, will see the full force of the storm, with winds of 45 - 55 mph. The northeastern portion of the Dominican Republic should get heavy rains from Maria, but not tropical storm-force winds. It now appears likely that the Turks and Caicos Islands and the Bahamas will miss seeing the core of Maria, but they are still in the cone of uncertainty, and cannot count on this yet. The reliable ECMWF model has now joined the other models in predicting that Maria will get caught up by a trough of low pressure early next week and turned northwards between Bermuda and U.S. East Coast. This has been the usual pattern this hurricane season, and we can now have moderate confidence that Maria will miss hitting the U.S., given the high degree of model agreement on this. A threat to southeast Newfoundland in Canada is possible for late next week, though.

I'll have an update late Saturday morning.

Jeff Masters

Hurricane

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Hottest U.S. summer in 75 years; La Niña is back; Nate and Maria update

By: JeffMasters, 2:32 PM GMT on September 09, 2011

The U.S. had its hottest summer in 75 years, and Texas smashed the record for hottest summer ever experienced by a U.S. state since record keeping began in 1895, NOAA's National Climatic Data Center said yesterday. The June - August average temperatures in Texas and Oklahoma were a remarkable 1.6°F and 1.3°F warmer than the previous hottest summer for a U.S. state, the summer of 1934 in Oklahoma. Texas' summer was 2.5°F hotter than their previous hottest summer, in 1998. Louisiana had its hottest summer on record in 2011, and the 4th hottest summer for any U.S. state since record keeping began in 1895. For the U.S. as a whole, the summer of 2011 was the 2nd warmest summer on record, just 0.1°F behind the notorious Dust Bowl summer of 1936. Fifteen states had a summer average temperature ranking among their ten warmest. Washington and Oregon were the only states across the lower 48 to have below-average summer temperatures. Texas also had its driest summer on record, with rainfall 5.29 inches (134.4 mm) below the long-term average, and 1.04 inches (26.4 mm) less than the previous driest summer in 1956. New Mexico had its second driest summer, Oklahoma its third driest summer, and New Jersey and California had their wettest summers on record. The U.S. Climate Extremes Index (CEI), which is sensitive to climate extremes in temperature, rainfall, dry streaks, and drought, indicated that an area nearly four times the average value was affected by extreme climate conditions during summer 2011. This is the third largest summer value of record, and came on the heels a spring season that was the most extreme on record. The CEI goes back to 1910.


Figure 1. Average temperatures for the summer in Texas and Oklahoma, at 86.8 degrees F (30.4 degrees C) and 86.5 degrees F (30.3 degrees C), respectively, exceeded the previous seasonal statewide average temperature record for any state during any season. The previous warmest summer statewide average temperature was in Oklahoma, during 1934, at 85.2 degrees F (29.6 degrees C). Image credit: National Climatic Data Center.

More bad news for Texas: La Niña is back
La Niña, which contributed to extreme weather around the globe during the first half of 2011, has re-emerged in the tropical Pacific Ocean and is forecast to gradually strengthen and continue into winter, NOAA announced yesterday. Over the past two weeks, ocean temperatures have cooled significantly in the Equatorial Pacific off the coast of South America. Ocean temperatures in the region 120°W - 170°W and 5°S - 5°N, called the Niño 3.4 region, were 0.6°C cooler than average over the first week of September. The threshold for a weak La Niña is temperatures 0.5° cooler than average, so we are now experiencing weak La Niña conditions. Drought conditions are common over the southern tier of states during a La Niña event, since the cooling of the equatorial Pacific waters usually pushes the jet stream such that rain-bearing low pressure systems pass through the Midwest and avoid the South. It is likely that the drought gripping Texas, Oklahoma, and New Mexico will continue well into 2012, due to the emergence of La Niña. La Niña events also typically cause wetter than normal winters in the Pacific Northwest and Ohio Valley, colder winters in the Pacific Northwest and northern Plains, and warmer temperatures in the southern states.


Figure 2. Departure of Sea Surface Temperature (SST) from average on September 8, 2011. Cooler than average waters in the equatorial East Pacific signify the emergence of La Niña. In the Atlantic, SSTs remain very warm in the Main Development Region between the coast of Africa and Central America, including the Caribbean. The Gulf of Mexico is cool where Tropical Storm Lee stirred up the water, and the waters off the Mid-Atlantic and New England coasts are cool due to the passage of Hurricane Irene. Image credit: NOAA/NESDIS.

Tropical Storm Nate
Tropical Storm Nate continues to remain nearly stationary in Mexico's Bay of Campeche. Latest visible satellite loops show that Nate is having trouble with the dry air to its north, which is getting wrapped into the circulation and interfering with intensification. Since the storm is stationary, it is upwelling cooler waters from the depths that are also slowing intensification. Wind shear has fallen to the low range, near 5 knots, so once Nate manages to wall off the dry air to its north and begin moving away from the pool of cool water beneath it, steady intensification should occur. Nate probably has time to intensify to a strong Category 1 hurricane, and perhaps a Category 2 hurricane, before making landfall Sunday in Mexico. The main hazard to Mexico will probably be very heavy rains that will cause flash flooding and mudslides. Thanks to last night's dropsonde mission by the NOAA jet, the computer models have now come into much better agreement on the future path of Nate. A ridge of high pressure is expected to build in to the north of the storm, forcing it westward or southwestward to a landfall in Mexico. Nate is too far south to be turned northwards towards Louisiana, as some model runs were suggesting yesterday.

Nate is a small storm, and is not likely to bring significant rains to Texas; only extreme South Texas near Brownsville could see an inch or so of rain over the weekend from an outer spiral band of Nate. Our latest wundermap wind forecast map from the European Center model, with the fire layer turned on, shows that Nate's wind field on Saturday and Sunday will not be large enough to fan the fires burning in Texas.


Figure 3. True-color MODIS image of Tropical Storm Nate taken at 1:40 pm EDT Thursday September 8, 2011. At the time, Nate was a tropical storm with 60 mph winds. Image credit: NASA.

Tropical Storm Maria
Tropical Storm Maria is not changing much in intensity it bears down on the Lesser Antilles Islands, data from an An Air Force Reserve hurricane hunter aircraft currently investigating the storm reveal. Top winds found by the aircraft at their flight level of 5,000 feet were just 48 mph as of 10am EDT, though some stronger surface winds were observed by their SFMR surface wind instrument. Satellite loops show that Maria's heavy thunderstorms have steadily increased in areal coverage and intensity this morning. Maria has grown into a very large tropical storm, and will bring heavy rains and strong gusty winds to nearly all of the islands in the Lesser Antilles. There is still a moderate 10 - 15 knots of wind shear affecting Maria, and this is slowing down intensification. Maria passed just south of buoy 41101 this morning. Sustained winds at the buoy ranged from 22 - 37 mph this morning, and the pressure dropped to 1003 mb. Martinique radar shows heavy rains from Maria are now affecting the islands, but the thunderstorms are not well-organized into spiral bands.

The intensity forecast models predicts steady strengthening for Maria, and I think likely that Maria will be a tropical storm with 50 - 60 mph winds in the Virgin Islands and Puerto Rico on Saturday, and develop into a Category 1 hurricane shortly after pulling away from Puerto Rico on Saturday night or Sunday morning. The northeastern portion of the Dominican Republic with get heavy rains from Maria, but not tropical storm-force winds. The computer models are unified on taking Maria across the Northern Lesser Antilles, Virgin Islands, and close to eastern Puerto Rico, but then diverge on how strong the steering influence a trough of low pressure forecast to move off the U.S. East Coast early next week will have. The majority of the models predict that the Turks and Caicos Islands and the Bahamas will miss seeing the core of Maria, and the storm will curve to the northwest and then north between the U.S. East Coast and Bermuda on a track that would likely take Maria near Newfoundland, Canada. However, two models--the very reliable ECMWF, and the less reliable NOGAPS--predict that Maria will not get picked up by the trough, and instead will plow straight through the Turks and Caicos Islands and Bahamas towards Florida. Given that the ECMWF model predicts an unrealistically weak storm and the NOGAPS model was our poorest-performing major model last year, I believe a more northerly path missing the Turks and Caicos Islands and Bahamas is more likely. We need a dropsonde mission by the NOAA jet to help reduce some of the track uncertainty, but unfortunately we have only one such airplane, and it is tied up flying missions for Tropical Storm Nate in the Gulf of Mexico.

Lee's rains trigger historic flooding in New York and Pennsylvania
Rivers in New York and Pennsylvania swollen by record rains from the remains of Tropical Storm Lee have mostly crested and are on their way down this morning, but it will likely be another day before many of the 120,000 people evacuated from the historic floods can return to their homes. Flooding in many areas of Pennsylvania and New York exceeded that of Hurricane Agnes of 1972, which did $11.8 billion in damage (2010 dollars), and was the costliest hurricane in Pennsylvania's history. Binghamton, New York received 8.48" of rain in the 24 hours ending at 8 am EDT yesterday. This is nearly double the previous all-time record set just last year, when 4.68" fell on Sep 30 - Oct. 1, 2010. Binghamton has also already broken its record for rainiest year in its history; records go back to 1890. The Susquehanna River at Binghamton crested at 25.71', its highest level since records began in 1847, and spilled over the flood walls protecting the city. Rainfall amounts in Pennsylvania were even greater, with Harrisburg receiving 13.30", and a storm-maximum 15.37" falling in Elizabethtown, Pennsylvania. In Wilkes-Barre, PA, the Susquehanna River crested at 38.83' at 1:45 am this morning, just below the 41' flood wall protecting the city. The flood walls were 37' back in 1972 when Hurricane Agnes' rains pushed the Susquehanna River to 41', flooding the downtown area with 9' of water, damaging or destroying 25,000 buildings and causing $1 billion in damage. It's a good thing the flood walls were raised to 41 feet, or else a repeat disaster would have occurred. The extreme rains were due to the slow-moving remains of Tropical Storm Lee as it interacted with a stationary front draped along the Eastern U.S. Adding to the potent moisture mix was a stream of tropical moisture associated with Hurricane Katia that collided with the stationary front.


Figure 4. The Susquehanna River at Binghamton has crested this afternoon at its highest flood height on record, 25.71'. Records at this gauge go back to 1847. Image credit: NOAA/AHPS.

I'll have an update this afternoon.

Jeff Masters

Climate Summaries Flood Hurricane

Updated: 2:39 PM GMT on September 09, 2011

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Nate almost a hurricane; Maria remains disorganized

By: JeffMasters, 9:05 PM GMT on September 08, 2011

An Air Force Reserve hurricane hunter aircraft is in Tropical Storm Nate, and has found winds much stronger than the storm's satellite appearance would suggest. At 2:17 pm EDT, the aircraft measured winds at their flight level of 1500 feet of 93 mph, which would ordinarily support upgrading Nate to a Category 1 hurricane. Surface winds measured by the SFMR instrument were about 70 mph, suggesting that Nate is indeed very close to hurricane strength. However, latest visible satellite loops show that if Nate is a hurricane, it's only half of a hurricane. Nate's low-level center is exposed to view, due to northeasterly upper-level winds that are creating a moderate 10 knots of wind shear. This shear is keeping all of Nate's heavy thunderstorms pushed to the south side of the center, and the northern half of the storm almost cloud-free. Sustained winds at Buoy 42055, about 140 miles to the northwest of the center of Nate, were just 28 mph at 3:50 pm EDT this afternoon. Water vapor satellite loops show that there is a large area of very dry air from Texas to the north of Nate, and this dry air is keeping the northern half of the storm dry.

Nate will meander in the Bay of Campeche for several days, and the computer models are sharply divided on what happens early next week to the storm. A ridge of high pressure is expected to build in to the north of the storm, potentially forcing it westwards to a landfall in Mexico. However, our two best-performing models last year, the GFS and ECMWF, predict that a weak trough of low pressure expected to move across the U.S. early next week will be strong enough to turn Nate northwards towards an eventual landfall along the northern Gulf Coast. We will have to wait until the NOAA jet makes its first mission to sample the steering currents in the Gulf of Mexico to get a better idea on how probable this northern path might be; their first flight will be tonight, and the data will make it into the 8 pm models runs that will be available first thing Friday morning. As far as intensity goes, the very dry air to Nate's north should begin being less of a problem for it by Friday, when the upper level winds shift more to blow from the southeast, and the shear drops to the low range, 5 - 10 knots. Since the storm is moving very slowly, it will upwell cooler waters from the depths that will slow intensification, though.


Figure 1. Afternoon satellite image of Nate.

Tropical Storm Maria
Tropical Storm Maria barely survived as a tropical storm today, but is now making a bit of a comeback. Satellite loops show that Maria has been badly ripped up by the 10 - 20 knots of wind shear affecting it. The low-level center has been exposed to view most of the day, and surface arc-shaped clouds have been racing away from the storm to the west this afternoon, indicating that dry air has been getting into Maria's thunderstorms and disrupting the storm. However, the areal coverage and intensity of Maria's thunderstorms have increased a little in the past two hours. Maria is passing close to buoy 41040, which measured sustained winds of 36 mph, gusting to 45 mph, at 2:50 pm EDT.

Wind shear is predicted to fall to the low range on Friday as Maria approaches the Lesser Antilles. In addition, as I noted in this morning's post, Maria will be encountering an atmospheric disturbance known as a Convectively-Coupled Kelvin Wave (CCKW) that is currently passing through the Lesser Antilles Islands. There is a great deal of upward-moving air in the vicinity of a CCKW, and will help strengthen the updrafts in Maria's thunderstorms, potentially intensifying the storm. None of our models are detailed enough to "see" CCKWs", so we may see more intensification of the storm than the models are calling for. I believe Maria will continue to organize and arrive in the Lesser Antilles Islands as a tropical storm with 50 - 60 mph winds. The latest run of the GFDL model predicts that Maria will be a Category 1 hurricane on Saturday afternoon when it moves through the Virgin Islands, and a Category 2 hurricane Sunday night when it moves through the Turks and Caicos Islands. This is on the high end of what is possible, and I think it more likely that Maria will be a tropical storm with 50 - 60 mph winds in the northern Lesser Antilles, 60 - 70 mph winds in the Virgin Islands and Puerto Rico, and a Category 1 hurricane in the Turks and Caicos Islands--assuming passage over Puerto Rico and the eastern tip of the Dominican Republic does not significantly disrupt the storm. A lower intensity, as forecast by NHC, is certainly quite possible, as Maria may continue to struggle with the dry air and wind shear besetting it.

The latest computer model runs have been trending more southwards, and the Northern Lesser Antilles, Virgin Islands, Puerto Rico, the Turks and Caicos Islands, and the Bahama Islands are all at high risk of a direct hit by Maria. The models are split on how strong the steering influence a trough of low pressure along the U.S. East Coast will have once Maria approaches the U.S. East Coast. Most of the models foresee that Maria will turn north before arriving at Florida, and potentially threaten North Carolina, Bermuda, or Canada. The latest run of the GFDL model, though, brings Maria through the Bahamas to a point just 100 miles southeast of Miami as a hurricane on Tuesday afternoon. While this forecast is an outlier, and it is more likely that Maria will turn north before reaching Florida, it will be another two days before we will have a fair degree of confidence on when Maria will curve to the north.

Lee's rains trigger historic flooding in New York and Pennsylvania
An extreme rainfall event unprecedented in recorded history has hit the Binghamton, New York area, where 7.49" of rain fell yesterday. This is the second year in a row Binghamton has recorded a greater than 1-in-100 year rain event; their previous all-time record was set last September, when 4.68" fell on Sep 30 - Oct. 1, 2010. Binghamton has also already broken its record for rainiest year in its history. Records go back to 1890 in the city. The rain has ended in Binghamton, with this morning's rain bringing the city's total rainfall for the 40-hour event to 9.02". The Susquehanna River at Binghamton has risen to 25.69', its highest level since records began in 1847, and is now spilling over the flood walls protecting the city, according to media reports. In Hershey, Pennsylvania, Swatara Creek is 19' over flood stage, and more than 9' above its record flood crest. Widespread flash flooding is occurring across the entire area, and over 120,000 people have been evacuated from their homes.


Figure 2. Seven-day precipitation amounts from Tropical Storm Lee and its remnants. Image credit: NOAA/AHPS.


Figure 3. The Susquehanna River at Binghamton has crested this afternoon at its highest flood height on record, 25.69'. Records at this gauge go back to 1847. Image credit: NOAA/AHPS.


Figure 4. In Hershey, Pennsylvania, Swatara Creek is 19' over flood stage, and more than 9' above its previous record flood crest. The river is forecast to crest at 27.2' (green lines are the predictions.) Records at this gage go back to 1930. Image credit: NOAA/AHPS.

The extreme rains are due the the remains of Tropical Storm Lee interacting with a stationary front draped along the Eastern U.S. Adding to the potent moisture mix last night was a stream of tropical moisture associated with Hurricane Katia that collided with the stationary front. You don't often see a major city break its all-time 24-hour precipitation record by a 60% margin, according to wunderground's weather historian, Christopher C. Burt, and he can't recall ever seeing it happen before. It's worth noting that the Susquehanna River Binghamton stream gage, which has been in operation since 1847, is due to be shut off in 3 weeks due to budget cuts. Here's the note at the USGS web site:

NOTICE (03/23/2011)--Data collection at this streamgage may be discontinued after October 1, 2011 due to funding reductions from partner agencies. Although historic data will remain accessible, no new data will be collected unless one or more new funding partners are found. Users who are willing to contribute funding to continue operation of this streamgage should contact Rob Breault or Ward Freeman of the USGS New York Water Science Center at 518-285-5658 or dc_ny@usgs.gov.

I'll have an update in the morning.

Jeff Masters

Flood Hurricane

Updated: 9:23 PM GMT on September 08, 2011

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1-in-100 year rains cause extreme flooding in NY, PA; Nate, Maria, and Katia

By: JeffMasters, 2:37 PM GMT on September 08, 2011

An extreme rainfall event unprecedented in recorded history has hit the Binghamton, New York area, where 7.49" fell yesterday. This is the second year in a row Binghamton has recorded a 1-in-100 year rain event; their previous all-time record was set last September, when 4.68" fell on Sep 30 - Oct. 1, 2010. Records go back to 1890 in the city. The skies have now cleared in Binghamton, with this morning's rain bringing the city's total rainfall for the 40-hour event to 9.02". However, another large region of rain lies just to the south in Pennsylvania, and all of the rivers in the surrounding region are in major or record flood. The Susquehanna River at Binghamton is at 25.18', its highest level since records began in 1847, and is expected to overtop the flood walls protecting the city this afternoon. In Hershey, Pennsylvania, Swatara Creek is 18' over flood stage, and more than 8' above its record flood crest. Widespread flash flooding is occurring across the entire area, and over 125,000 people have been evacuated from their homes.


Figure 1. Radar-observed rainfall from the Binghamton, NY radar.


Figure 2. The Susquehanna River at Binghamton is at its highest flood height on record this morning (25 feet.) Records at this gauge go back to 1847. Image credit: NOAA/AHPS.


Figure 3. In Hershey, Pennsylvania, Swatara Creek is 18' over flood stage, and more than 8' above its record flood crest. Records at this gage go back to 1930. Image credit: NOAA/AHPS.

The extreme rains are due the the remains of Tropical Storm Lee interacting with a stationary front draped along the Eastern U.S. Adding to the potent moisture mix last night was a stream of tropical moisture associated with Hurricane Katia that collided with the stationary front. You don't often see a major city break its all-time 24-hour precipitation record by a 60% margin, according to wunderground's weather historian, Christopher C. Burt, and he can't recall ever seeing it happen before. It's worth noting that the Susquehanna River Binghamton stream gage, which has been in operation since 1847, is due to be shut off in 3 weeks due to budget cuts. Here's the note at the USGS web site:

NOTICE (03/23/2011)--Data collection at this streamgage may be discontinued after October 1, 2011 due to funding reductions from partner agencies. Although historic data will remain accessible, no new data will be collected unless one or more new funding partners are found. Users who are willing to contribute funding to continue operation of this streamgage should contact Rob Breault or Ward Freeman of the USGS New York Water Science Center at 518-285-5658 or dc_ny@usgs.gov.

Tropical Storm Nate
Tropical Storm Nate formed in the southern Gulf of Mexico yesterday afternoon after the Hurricane Hunters found a well-defined surface circulation and 45 mph surface winds. Nate is the 14th named storm this year, and comes three days before the climatological half-way point of the Atlantic hurricane season, September 10. A typical hurricane season has just 10 - 11 named storms, so we've already had 35% more than a whole season's worth of storms before reaching the season's half-way point. At this rate, 2011 will see 28 named storms, equaling the all-time record set in 2005. Nate's formation date of September 7 puts 2011 in 2nd place for earliest date of arrival of the season's 14th storm. Only 2005 had an earlier formation date of the season's 14th named storm (September 6, when Hurricane Nate got named.) Third place is now held jointly by 1936 and 1933, which got their 14th storm of the season on September 10.

Latest visible satellite loops show that Nate's low-level center is exposed to view, due to northeasterly upper-level winds that are creating a moderate 10 knots of wind shear. This shear is keeping all of Nate's heavy thunderstorms pushed to the south side of the center. Sustained winds at Buoy 42055, about 100 miles to the northwest of the suspected center of Nate, were north at 31 mph at 6:50 am CDT this morning. We haven't had a hurricane hunter aircraft in the storm since yesterday afternoon, and the next plane is due to arrive near 2 pm this afternoon. Water vapor satellite loops show that here is a large area of very dry air from Texas to the north of Nate, and this dry air is probably interfering with the storm's development.

Up until last night's 8 pm EDT runs of the computer models, the models were in general agreement that Nate would meander in the Bay of Campeche for several days, until a ridge of high pressure built in to the north of the storm, forcing it westwards to a landfall in Mexico. However, the latest 2 am EDT run by the GFS model predicts that Nate may gain enough latitude to escape being forced westwards by the ridge, and instead move northwards to make a landfall along the U.S. Gulf Coast. The GFDL, which uses the GFS for its initial conditions, is also on board with this idea, as is the HWRF model, to a lesser degree. The 2 am EDT run of the NOGAPS model did not go along with this idea, though. We will have to wait until the NOAA jet makes its first mission to sample the steering currents in the Gulf of Mexico to get a better idea on how probable this northern path might be; their first flight will be tonight, and the data will make it into the 8 pm models runs that will be available first thing Friday morning. As far as intensity goes, the very dry air to Nate's north should begin being less of a problem for it by Friday, when the upper level winds shift more to blow from the southeast, and the shear drops to the low range, 5 - 10 knots. Since the storm is moving very slowly, it will upwell cooler waters from the depths that will slow intensification, though. The earliest Nate would become a hurricane is probably on Saturday.


Figure 2. GOES-13 image of Hurricane Katia, Tropical Storm Maria, and Tropical Storm Nate taken at 8 am EDT September 8, 2011. Image credit: NASA/GSFC.

Tropical Storm Maria
Tropical Storm Maria is midway between the Northern Lesser Antilles Islands the coast of Africa, and due to arrive in the Northern Lesser Antilles late Friday night or Saturday morning. Satellite loops show that Maria has been ripped up pretty badly by the 10 - 20 knots of wind shear affecting it, with the low-level center exposed to view, and a few disorganized clumps of heavy thunderstorms lying to the west and northeast of the center. Water vapor satellite images show that Maria is embedded in a very moist environment. Ocean temperatures are near 28.5°C, which is 2°C above the 26.5°C threshold usually needed to sustain a tropical storm. Maria passed just south of Buoy 41041 this morning, and top sustained winds during passage were 42 mph, gusting to 56 mph. Maria will pass close to buoy 41040 near 8pm EDT tonight.

With wind shear predicted to continue in the moderate range for the next five days, and the storm struggling to maintain its circulation, strengthening of Maria to a hurricane before it reaches the Lesser Antilles seems unlikely at this time. None of the intensity models are calling for Maria to reach hurricane strength until well after the storm passes Puerto Rico. However, Mike Ventrice, a meteorology Ph.D. student at the University of Albany, pointed out to me yesterday that a atmospheric disturbance known as a Convectively-Coupled Kelvin Wave (CCKW) is passing through the Lesser Antilles Islands today, and is headed eastwards towards Maria at 25 mph. Maria will encounter this CCKW Thursday night or Friday morning. There is a great deal of upward-moving air in the vicinity of a CCKW, and will help strengthen the updrafts in Maria's thunderstorms, potentially intensifying the storm. None of our models are detailed enough to "see" CCKWs", so we may see more intensification of the storm than the models are calling for. Given the disorganized state Maria is currently in, though, the extra boost in upward motion provided by the CCKW may not make of a difference to the storm.

The track forecasts for Maria from the various models agree that the storm will affect the Northern Lesser Antilles Islands, Virgin Islands, and Puerto Rico. After it passes the Lesser Antilles, Maria has the usual amount of high uncertainty in its 5 - 7 day track forecast. The models are split on how strong the steering influence a trough of low pressure along the U.S. East Coast will have. The UKMET model prefers a more southerly track for Maria through the Turk and Caicos Islands and the Bahamas towards the U.S. East Coast, while the other models predict a more northwesterly track, with a potential threat to Bermuda. Climatology favors a track that would miss the U.S., with Dr. Bob Hart's track history pages suggesting that Maria has a 14% chance of hitting Canada, 5% chance of hitting Bermuda, and an 18% chance of hitting North Carolina.

Hurricane Katia
Hurricane Katia has brought a few rain showers and some gusty winds of 20 - 30 mph to Bermuda last night and this morning, but is not going to bring hazardous weather to the island as the storm makes it swing around Bermuda today and tomorrow. Latest satellite loops show that Katia is a shadow of its former Category 4 self, as dry air has eaten into the southwest side of the storm into the eye. Katia's outer rainbands should remain just offshore from North Carolina, New England, and the Canadian Maritime provinces at the point of closest approach. The main impact of Katia will be a multi-day period of high surf leading to beach erosion and dangerous rip currents.

I'll have an update this afternoon.

Jeff Masters

Flood Hurricane

Updated: 3:06 PM GMT on September 08, 2011

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Tropical Storms Nate, Maria have formed; 2011 season on the heels of 2005's numbers

By: JeffMasters, 11:25 PM GMT on September 07, 2011

Tropical Storm Nate formed in the southern Gulf of Mexico this afternoon after Hurricane Hunters found a well-defined surface circulation in Invest 96L. Nate is the 14th named storm this year, and comes three days before the climatological half-way point of the Atlantic hurricane season, September 10. A typical hurricane season has just 10 - 11 named storms, so we've already had 35% more than a whole season's worth of storms before reaching the season's half-way point. At this rate, 2011 will see 28 named storms, equalling the all-time record set in 2005. Nate's formation date of September 7 puts 2011 in 2nd place for earliest date of arrival of the season's 14th storm. Only 2005 had an earlier formation date of the season's 14th named storm (September 6, when Hurricane Nate got named.) Third place is now held jointly by 1936 and 1933, which got their 14th storm of the season on September 10.

This afternoon's Hurricane Hunter mission into Invest 96L/Nate found maximum sustained winds of at least 45 mph, and minimum central pressure of 1003 mb. Wind shear in the region is low and is expected to remain low for the next 48 hours. Sea surface temperature is toasty in the Gulf at around 30°C (86°F) and more than ample to support intensification. Nate will bring heavy rains and potential flooding and mudslides to Mexico, and according to some weather models, also has the potential to be a U.S. landfall threat. Nate's surface circulation is apparent on satellite loops, although the thunderstorm activity in the storm is displaced from the center. It appears the strongest storms are to the southwest and northeast of the center. East of the storm, thunderstorms are churning associated with the stationary front that's draped across Florida, the Gulf of Mexico, and over the Yucatan Peninsula. This stationary front is left over from the cold front that pushed south through the central and eastern U.S. earlier this week, and created a focal point in the Gulf of Mexico for Tropical Storm Nate to form. It's notoriously difficult for weather models and forecasters to predict tropical cyclones that spin up in the Gulf of Mexico, but lead-time for both Nate and our previous Gulf cyclone, Lee, was generous.


Figure 1. Infrared satellite image of Tropical Storm Nate at 6:15pm EDT.

Forecast for Tropical Storm Nate
Given the favorable environment, in addition to a very warm pocket of sea surface waters in the central Gulf of Mexico, we expect that Nate will intensify modestly over the next few days. The National Hurricane Center forecasts that Nate will become the third hurricane of the season by Friday. The HWRF and ECMWF agree with this forecast—both of these models bring Nate to a category 2 hurricane by Saturday. The IVCN/ICON consensus models that the Hurricane Center relies on are more conservative, peaking at category 1 intensity. Nate's maximum potential intensity is heavily dependent on its track, which, according to the weather models, has been up in the air for the past few of days. Until this afternoon's run, the ECMWF has held true to its forecast that Nate will track north and make landfall anywhere from Louisiana to Florida. This afternoon, it backed off of that solution and is now forecasting a northern Mexico landfall. The GFS has consistently forecasted a track that lingers in the Bay of Campeche for a few days before ultimately making dive to the west into Mexico. Over the past few days the Canadian CMC model has been reluctant to develop Nate at all, but today is forecasting the system to track north into the Southeast U.S. states. Now that there is Hurricane Hunter data to ingest (as well as confirmed 45 mph surface wind speeds), we expect the models will come into better agreement on both track and intensity for Tropical Storm Nate.

Tropical Storm Maria

Tropical Depression 14 was named Tropical Storm Maria late this morning, as well. The storm is still pretty far east in the Atlantic, 1,200 miles east of the Leeward Islands, but is moving quickly to the west at 23 mph. According to the National Hurricane Center, Maria looks well-organized on satellite, "but not really." If you look closely at satellite loops (especially the loops that you can catch before the sun sets in that area), you'll see the surface circulation is located to the west of the strongest thunderstorm activity. Well-organized tropical cyclones will be vertically stacked in the atmosphere, with the strongest thunderstorms directly on top of the surface circulation. Maria's disjointed-ness is likely due to a pretty strong clip of wind shear (30 knots worth) in the area. This would usually be deadly for a tropical cyclone of Maria's strength, but since the storm is moving so quickly to the west, the Hurricane Center is forecasting the storm to remain somewhat intact for the next 5 days, although the forecast is for no intensification. Models are coming into better agreement on the track of this system. Prior to today, the ECMWF was forecasting a track south of Puerto Rico, but has since changed its mind and is now in agreement with many of the other models on a track skirting the northern Leeward Islands and missing the Greater Antilles to the north. Beyond this, there is quite a bit of uncertainty depending on steering winds in the Atlantic. It's still too early to guess which track the models will eventually converge on. Climatology favors a track that would miss land, with Dr. Bob Hart's track history pages suggesting Maria has a 22% chance of hitting Canada, 19% chance of hitting Bermuda, and an 11% chance of hitting North Carolina.

Angela

Hurricane

Updated: 1:13 AM GMT on September 08, 2011

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TD 14 likely to become Maria; new Gulf of Mexico system brewing

By: JeffMasters, 1:32 PM GMT on September 07, 2011

Tropical Depression Fourteen formed yesterday from a strong tropical wave that moved off the coast of Africa early this week, and is headed west-northwest towards an encounter with the Northern Lesser Antilles Islands. Satellite loops show a large a steadily organizing system with plenty of heavy thunderstorm activity, good upper-level outflow to the north and west, and some respectable low-level spiral bands beginning to form. TD 14 is probably a tropical storm now, and is very likely to be named Tropical Storm Maria later today. Water vapor satellite images show that 95L is embedded in a very moist environment. Ocean temperatures are near 28.5°C, which is 2°C above the 26.5°C threshold usually needed to sustain a tropical storm. With wind shear predicted to remain low to moderate the next five days, the atmosphere expected to stay moist, and ocean temperatures predicted to gradually warm, TD 14 should generally show a strengthening trend. Curiously, most of the intensity forecast models show little strengthening of TD 14, so NHC is keeping their intensity forecast lower than is typical for a storm in these conditions at this time of year.

The track forecasts for TD 14 from the various models agree that the storm will affect the Northern Lesser Antilles Islands, though there are some differences in forward speed, resulting in some uncertainty whether the storm will arrive at the islands as early as Friday night, or as late as Saturday afternoon. After it passes the Lesser Antilles, TD 14 has the usual amount of high uncertainty in its 5 - 7 day track forecast. The models are split on how strong the steering influence a trough of low pressure along the U.S. East Coast will have. The ECMWF and UKMET models prefer a more southerly track for TD 14 through the Bahamas towards the U.S. East Coast, while the GFS, NOGAPS, and HWRF models predict a more northwesterly track, with a potential threat to Bermuda. It's too early to guess which track the models will eventually converge on. Climatology favors a track that would miss land, with Dr. Bob Hart's track history pages suggesting TD 14 has a 22% chance of hitting Canada, 19% chance of hitting Bermuda, and an 11% chance of hitting North Carolina.


Figure 1. Morning satellite image of TD 14.

Gulf of Mexico disturbance 96L
A cold front swept into the Gulf of Mexico off the coast of Texas behind Tropical Storm Lee on Monday, and has stalled out along a line from Tampa, Florida to Mexico's Bay of Campeche in the southern Gulf of Mexico. Heavy thunderstorms have begun to build along the tail end of this front in the Bay of Campeche, and this disturbance has been designated Invest 96L by NHC. Latest visible satellite loops do not show that 96L has a closed surface circulation yet, but buoy and surface observations along the coast of Mexico suggest that there may be a large-scale counter-clockwise circulation present over the Bay of Campeche. Sustained winds at Buoy 42055, about 100 miles to the northwest of the suspected center of 96L, were northeast at 27 mph at 6:50 am CDT this morning. Water vapor satellite loops show that here is a large area of very dry air from Texas to the north of 96L, and this dry air may interfere with 96L's development. A hurricane hunter mission is scheduled for this afternoon into 96L.

Most of the computer models develop 96L into a tropical depression in the next 1 - 2 days, and these same models did very well at anticipating the formation of Tropical Storm Lee in the Gulf of Mexico last week. Given the moderate wind shear, warm waters, and presence of an old cold front to serve as a nucleus for development, I give 96L an 80% chance of becoming a tropical depression over the next tow days, a bit higher than the 60% probability NHC is going with. Steering currents are weak in the Bay of Campeche, making for a lot of uncertainty in where 96L might go. The only model predicting a U.S. landfall is the ECMWF, which predicts 96L might hit between Louisiana and the Florida Panhandle on Monday. A more popular solution is for the storm to meander in the Bay of Campeche for many days, and eventually make landfall on the coast of Mexico between Veracruz and Tampico. None of the models is hinting at a track towards Texas, and the intense dome of high pressure associated with their record drought and heat wave will tend to discourage any tropical cyclones from making a Texas landfall over the coming seven days.

Hurricane Katia
Hurricane Katia continues to the northwest as a Category 1 hurricane with 90 mph winds. Latest satellite loops show that dry air has eaten into the southwest side of the storm. The computer models continue to agree that a low pressure system over the Eastern U.S. associated with the remnants of Tropical Storm Lee will turn Katia to the north. As the storm moves northwards past North Carolina, Katia will get caught up in west-to-east moving winds associated with the jet stream, and taken northeastwards out to sea. No land areas are in Katia's cone of uncertainty, and Katia's outer rainbands should remain just offshore from North Carolina, New England, and the Canadian Maritime provinces at the point of closest approach. Bermuda may see a few rain showers from Katia, but the storm will not cause hazardous weather there. The main impact of Katia will be a multi-day period of high surf leading to beach erosion and dangerous rip currents. The East Coast is lucky that Tropical Storm Lee came along, since Lee helped to create the steering pattern that will keep Katia from hitting the U.S.


Figure 2. GOES-13 image of Hurricane Katia and the remains of Tropical Storm Lee, taken at 11:45 am EDT Tuesday September 6, 2011. At the time, Katia was a Category 3 hurricane with 120 mph winds. Image credit: NOAA Visualization Laboratory.

Heavy rains from Lee create significant flooding, tornadoes
Tropical Storm Lee is no more, but its remnants are marching slowly northeastwards along a stalled cold front, bringing torrential rains. Fortunately, the dry soils that were present before the event started have helped keep river flooding in the minor to moderate range. No river is currently at major flood stage as a result of rains from Tropical Storm Lee. Soils are at near-average moisture levels in Central Pennsylvania, where Lee's remnants are expected to drop 3 - 5 inches of rain over the next two days. These rains should cause moderate but not major flooding in Pennsylvania. Also of concern is the potential for tornadoes today. NOAA's Storm Prediction Center (SPC) has logged 40 tornado reports over the past four days from Lee, including two in North Carolina yesterday. Most of these tornadoes have been weak EF-0 and EF-1 twisters. A tornado that hit Cana, Virginia at Sunday night ripped the roof off of a gas station and injured two people. More tornadoes are likely today over coastal Virginia, Maryland, Delaware, and Southern New Jersey, where SPC is predicting a "Slight Risk" of severe weather.

Lee's heaviest rain amounts, by state, as of 4 am CDT today:

Holden, LA: 15.43"
Waveland, MS: 14.11"
Fyffe, AL: 12.94"
Cleveland, TN: 12.22"
Rome, GA: 11.01"
Milton, FL: 10.03"
Blowing Rock, NC: 7.18"
Fancy Gap, VA: 6.77"
Cranks Creek Reservoir, KY: 5.49"
Andover, NJ: 5.06"
Montgomery, NY: 4.23"
Pittsfield, MA: 3.90"
Bluefield, WV: 3.76"
Bridge City, TX: 3.12"
Keene, NH: 3.64"
Hagerstown, MD: 3.60"
Norwalk, CT: 3.20"
Wilmington, DE: 2.63"
Woodford, VT: 2.63"
Washington, DC: 2.42"

Jeff Masters

Hurricane

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Texas fires will diminish today; Lee's rains set all-time records

By: JeffMasters, 1:27 PM GMT on September 06, 2011

East Texas' dangerous fires continued to rage out of control yesterday, thanks to gusty north winds associated with the passage of a cold front and the remnant circulation of Tropical Storm Lee. Since Saturday, wildfires have torched over 500 homes in East Texas and killed two people. At Austin Bergstrom Airport, sustained winds of 20 - 25 mph, gusting to 30 - 35 mph blew much of the day yesterday. Tropical Storm Lee's remnants didn't bring any clouds or moisture to Austin yesterday, and the temperature climbed to 91°, with a humidity of just 11%. With the region enduring it's driest 1-year drought on record, yesterday's heat, dryness, and winds resulted in critical fire conditions. The forecast today for Austin is much better--winds will be only 5 - 10 mph, which should give firefighters the upper hand in many of the blazes, despite low humidities that will be in the 15 - 25% range. NOAA's Storm Prediction Center is not predicting that critical fire weather conditions will return during the remainder of the week. You can monitor today's fire activity by using our wundermap for Austin with the fire layer turned on.


Figure 1. True-color image taken by NASA's Aqua satellite of the the fires burning near Austin, Texas on September 5, 2011. Image credit: NASA.


Video 1. Video shot by a motorist on Highway 21 near Austin, Texas of the smoke from the fires that raced through Bastrop County on September 4, 2011.The highway closes and the motorist is forced to turn around.

Texas' unprecedented heat
As I reported in yesterday's post, there has never been a Texas summer hotter than the summer of 2011. The summer of 2011 now holds every major heat record for the city of Austin, including most 100° days (67 so far), hottest month in recorded history (August, breaking the previous record by a remarkable 2.1°), hottest summer (by 1.1°), and hottest day in history (112°F, tied with Sep, 5, 2000.) As wunderground's weather historian Christopher C. Burt documents in his latest blog post, the situation is similar across the rest of the state. Seventeen major cities in Texas recorded their hottest summer on record in 2011. Most of these stations had records extending back more than 100 years, and several of the records were smashed by an amazing 3.4°F--at Lubbock and at Wichita Falls. Neighboring states also experienced unprecedented heat, with Oklahoma recording America's hottest month by any state in recorded history during July, and Shreveport, Louisiana breaking its record for hottest month by 3°F in August. Mr. Burt commented to me: " I do not believe I have ever seen a site with a long period of record, like Shreveport, where records go back to 1874, break its warmest single month on record by an astonishing 3°. This is unheard of. Usually when a site breaks its single month temperature record, we are talking about tenths of a degree, rarely a whole degree, let alone 3 degrees! Hard to believe, frankly." Texas has also had its worst fire season on record, with over 3.5 million acres burned this year, and it's driest 1-year period in recorded history.


Figure 2. Observed soil moisture for Sunday Sep 4, 2011. Soil moisture is expressed in percent, with 50% being a historically average soil moisture level. Very dry soils, with moistures in the driest 1% - 30% in history (red and orange colors), were present over much of the south, where Lee dropped its heaviest rains. These dry soils have limited flooding damage. Image credit: N OAA Climate Prediction Center.

Heavy rains from Lee create significant flooding
Tropical Storm Lee is no more, but its remnants are marching slowly northeastwards along a stalled cold front, bringing torrential rains. Jackson, Mississippi received 11.68" in a 24 hour period yesterday, which is that city's heaviest 24-hour rainfall on record, according to wunderground's weather historian, Christopher C. Burt. Their previous record was 8.54", set April 11 -12, 1979. Fortunately, Jackson was in severe drought, and the dry soils were able to absorb a significant amount of rain before the local rivers began flooding. The Pearl River at Jackson rose above flood stage this morning, and is expected to crest at moderate flood stage late this week. Chattanooga, Tennessee also set its record for the wettest 24-hour period in its history, with 9.85" falling yesterday. The previous record was 7.61", set on March 30, 1886. Again, the dry soils that were present before the event started will help keep river flooding in the minor to moderate range on area rivers. Soils are at near-average moisture levels in Central Pennsylvania, where Lee's remnants are expected to drop over seven inches of rain over the next two days. These rains should cause moderate and possibly major flooding in Pennsylvania. Also of concern is the potential for tornadoes today. NOAA's Storm Prediction Center (SPC) has logged 25 tornado reports over the past three days from Lee, including three near Atlanta, Georgia yesterday. More tornadoes are likely today over North Carolina, Southern Virginia, and Northern South Carolina, where SPC is predicting a "Slight Risk" of severe weather.

Lee's heaviest rain amounts, by state, as of 4 am CDT today:

Holden, LA: 15.43"
Florence, MS: 13.45"
Tillman's Corner, AL: 11.74"
Milton, FL: 10.03"
Chattanooga, TN: 9.85"
Rome, GA: 5.70"
Roanoake, VA: 4.30"
Bluefield, WV: 3.14"
Bridge City, TX: 3.12"
Flatwoods, KY: 3.67"


Figure 3. Predicted rainfall for the 2-day period 8am EDT Tuesday - 8 am EDT Thursday, Sep 8, 2011. Lee's remnants are expected to bring a large swath of 7+ inches of rain into Central Pennsylvania. Image credit: NOAA/HPC.

Hurricane Katia
Hurricane Katia strengthened this morning into the Atlantic's first Category 4 hurricane of the year, but has slipped slightly in intensity due to an eyewall replacement cycle, and is now a strong Category 3 hurricane with 125 mph winds. Latest satellite loops show that the eye has now disappeared, and the hurricane is having trouble maintaining its eyewall in the face of moderate wind shear of 10 - 15 knots on its northwest side. Continued weakening to a Category 2 storm is a possibility, though Katia will probably re-strengthen later today or on Wednesday once it manages to build a new eyewall.

The computer models continue to agree that a low pressure system over the Eastern U.S. associated with the remnants of Tropical Storm Lee will turn Katia to the north well before the storm reaches the U.S. As the storm moves northwards past North Carolina, Katia will get caught up in west-to-east moving winds associated with the jet stream, and taken northeastwards out to sea. No land areas are in Katia's cone of uncertainty, and Katia's outer rainbands should remain just offshore from North Carolina, New England, and the Canadian Maritime provinces at the point of closest approach. The main impact of Katia will be high surf leading to beach erosion and dangerous rip currents. Long period swells from Katia have arrived at the coast, and the entire U.S. East Coast will receive an extended multi-day period of high surf. The East Coast is lucky that Tropical Storm Lee came along, since Lee helped to create the steering pattern that will keep Katia from hitting the U.S.


Figure 4. Morning satellite image of Hurricane Katia.

95L off the coast of Africa
A large tropical wave with plenty of intense thunderstorm activity and spin is located about 700 miles west-southwest of the Cape Verde Islands off the coast of Africa. This wave, Invest 95L, is under a moderate 10 - 20 knots of wind shear, and is headed west to west-northwest at 15 mph. Recent satellite loops show that 95L has an elongated circulation center; this will need to tighten up into a more circular shape before the storm can become a tropical depression. Water vapor satellite images show that 95L is embedded in a very moist environment. Ocean temperatures are near 28°C, which is 1.5°C above the 26.5°C threshold usually needed for a tropical storm to form. With wind shear predicted to remain low to moderate the next four days, the atmosphere expected to stay moist, and ocean temperatures predicted to gradually warm, I don't see anything that would keep 95L from becoming a tropical depression in 1 - 2 days. NHC is giving 95L a 70% chance of developing into a tropical depression by Thursday. There is a large amount of model support for development of 95L into a tropical depression, with most of the models predicting it could be a weak tropical storm by the time it reaches the Northern Lesser Antilles Islands on Friday or Saturday. Residents of the islands should anticipate the possibility of tropical storm conditions arriving as early as Friday. Most of the models predict 95L will follow a path near or slightly north of the Northern Lesser Antilles and Puerto Rico, then curve northwestwards, on a trajectory that would likely miss the Bahamas.

New Gulf of Mexico disturbance
A cold front swept into the Gulf of Mexico off the coast of Texas behind Tropical Storm Lee yesterday morning, and has stalled out along a line from Tampa, Florida to Mexico's Bay of Campeche in the southern Gulf of Mexico. Heavy thunderstorms have begun to build along the tail end of this front in the Bay of Campeche, but are still not very concentrated or organized. Most of the computer models develop a tropical depression in the Bay of Campeche late this week, and these same models did very well at anticipating the formation of Tropical Storm Lee in the Gulf of Mexico last week. Given the moderate wind shear, warm waters, and presence of an old cold front to serve as a nucleus for development, a new Gulf of Mexico tropical depression by late this week appears likely. The path such a storm might take would depend strongly on where the center forms. A more northerly formation location near the top of Mexico's Yucatan Peninsula would likely result in a northward motion towards the Florida Panhandle. This is the solution of the European Center Model (ECMWF), which takes a weak tropical storm with a central pressure of 1000 mb into the Florida Panhandle on Sunday. A more southerly formation location might lead to the storm getting trapped in a region of weak steering currents, resulting in a slow, erratic motion in the southern Gulf. This is the solution of the latest runs of the GFS, NOGAPS, and UKMET models. NHC is giving this disturbance a 20% chance of developing into a tropical depression by Thursday.


Figure 5. Volunteers with Portlight.org disaster relief charity take a break from their Hurricane Irene relief efforts in Pink Hill, NC. From their latest blog post:Please help as you can. And please remember in your thoughts and prayers those in the path of Irene.

Jeff Masters

Fire Flood Hurricane

Updated: 3:46 PM GMT on September 06, 2011

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Lee's winds fan deadly Texas fires; a dangerous day for Lee's floods and tornadoes

By: JeffMasters, 4:43 PM GMT on September 05, 2011

Texas' unprecedented heat wave and drought turned deadly yesterday when fires fanned by Tropical Storm Lee's gusty winds swept through East Texas, torching 300 homes near Austin, and killing a woman and her 18-month old daughter who couldn't escape the flames in Gladewater. At Austin Bergstrom Airport yesterday afternoon, the counter-clockwise circulation around Tropical Storm Lee brought sustained winds of 25 mph, gusting to 31. Lee didn't bring any clouds or moisture to Austin, and the afternoon high hit 102°, with a humidity of 22%. With the region enduring it's driest 1-year drought on record, yesterday's heat, dryness, and winds resulted in extremely critical fire conditions. The forecast today for Austin is marginally better--temperatures will be cooler, only reaching the upper 80s, but strong winds of 20 - 25 mph will continue to blow, and the atmosphere will be drier, with humidities in the 15 - 25% range. NOAA's Storm Prediction Center has declared a "Critical" fire weather danger area for East Texas today, one level below yesterday's "Extremely Critical" conditions. You can monitor today's fire activity by using our wundermap for Austin with the fire layer turned on. The summer of 2011 now holds every major heat record for the city of Austin, including most 100° days (67 so far), hottest month in recorded history (August, breaking the previous record by a remarkable 2.1°), hottest summer (by 1.1°), and hottest day in history (112°F, tied with Sep, 5, 2000.)

Texas' unprecedented heat
For as long as people have been taking weather measurements in Texas, there has never been a summer hotter than the summer of 2011. As wunderground's weather historian Christopher C. Burt documents in his latest blog post, seventeen major cities in Texas recorded their hottest summer on record in 2011. Most of these stations had records extending back more than 100 years, and several of the records were smashed by an amazing 3.4°F--at Lubbock and at Wichita Falls. Neighboring states also experienced unprecedented heat, with Oklahoma recording America's hottest month by any state in recorded history during July, and Shreveport, Louisiana breaking its record for hottest month by 3°F in August. Mr. Burt commented to me: " I do not believe I have ever seen a site with a long period of record, like Shreveport, where records go back to 1874, break its warmest single month on record by an astonishing 3°. This is unheard of. Usually when a site breaks its single month temperature record, we are talking about tenths of a degree, rarely a whole degree, let alone 3 degrees! Hard to believe, frankly." Texas has also had its worst fire season on record, with over 3.5 million acres burned this year, and it's driest 1-year period in recorded history.


Figure 1. Observed rainfall for the seven-day period ending at 8 am EDT Monday Sep 5, 2011. Tropical Storm Lee had dumped in excess of ten inches of rain sections of Louisiana and Mississippi (pink colors). Image credit: NOAA/AHPS.

Heavy rains from Lee creating dangerous flooding situation
Tropical Storm Lee has been absorbed by a cold front, and is no longer a tropical depression. However, the remnants of Lee are bringing torrential rains to the South and Appalachians today, and pose a serious flood threat. NOAA's latest Quantitative Precipitation Forecast warns that "an excessive and life-threatening rainfall event will be unfolding today and tonight across the Tennessee Valley and also the Southern Appalachians." A wide region of 4 - 8 inches of rain is expected along the path of Lee's remnants as they slide northeastwards along the front. These rains will likely accumulate later this week to 2 - 3 inches over New England regions devastated by Hurricane Irene's floods. Also of concern is the potential for tornadoes today. NOAA's Storm Prediction Center has logged 22 tornado reports so far from Lee, and today promises to be the most serious day for tornadoes yet, with SPC predicting a "Moderate Risk" of tornadoes across the South. Lee's heaviest rain amounts, by state, as of 10 am CDT today:

Holden, LA: 15.43"
Florence, MS: 13.45"
Mobile, AL: 11.35"
Milton, FL: 10.03"
Cumberland City, TN: 5.09"
Bridge City, TX: 3.12"
Plum Springs, KY: 3.10"


Figure 2. Predicted rainfall for the 5-day period 8am EDT Monday - 8 am EDT Saturday, Sep 10, 2011. Lee's remnants are expected to bring a large swath of 4+ inches of rain all the way to Pennsylvania. Image credit: NOAA/HPC.


Figure 3. Severe weather risk for Monday, September 5, 2011.

Hurricane Katia
Hurricane Katia is close to major hurricane strength, and is now a high-end Category 2 hurricane with 110 mph winds. Latest satellite loops show a well-defined eye and good upper-level outflow on all sides, but the hurricane still has a lopsided appearance, due to the impacts of dry air and moderate wind shear on its south side.

The computer models have finally come into agreement on the long-range future of Katia, determining that the trough of low pressure that will develop over the Eastern U.S. later this week will turn the hurricane to the north well before the storm reaches the U.S. As the storm moves northwards past North Carolina, Katia will get caught up in west-to-east moving winds associated with the jet stream, and taken northeastwards out to sea. No land areas are in Katia's cone of uncertainty, though Newfoundland, Canada will need to watch future forecasts to see how close Katia may pass to the southeastern portion of that province. The main impact of Katia will be high surf leading to beach erosion and dangerous rip currents. Long period swells from Katia are arriving at the Southeast U.S. coast today, and the entire U.S. East Coast will receive an extended multi-day period of high surf.


Figure 4. Afternoon satellite image of Hurricane Katia.

95L off the coast of Africa
A large tropical wave with plenty of intense thunderstorm activity and spin is located about 500 miles southwest of the Cape Verde Islands off the coast of Africa. This wave, Invest 95L, is under a moderate 10 - 20 knots of wind shear, and is headed west at 15 mph. Water vapor satellite images show that 95L is embedded in a very moist environment. Ocean temperatures are near 28°C, which is 1.5°C above the 26.5°C threshold usually needed for a tropical storm to form. With wind shear predicted to drop to the low range tomorrow, I don't see anything that would keep 95L from becoming a tropical depression in two or so days. NHC is giving 95L a 20% chance of developing into a tropical depression by Wednesday; given the storm's rather impressive organization and spin apparent on recent satellite loops, I'd put these odds at 40%. The NOGAPS model predicts 95L will develop by Saturday, a few hundred miles north of the Northern Lesser Antilles Islands, but this storm could just as easily pass directly through the Lesser Antilles on Saturday or Sunday, and develop into a tropical storm much sooner. If you plan on being in the Lesser Antilles Islands this weekend, pay attention to 95L.

New Gulf of Mexico disturbance
A cold front swept into the Gulf of Mexico off the coast of Texas behind Tropical Storm Lee early this morning. The front is expected to continue to the east and stall out Tuesday and Wednesday along a line from Louisiana to Mexico's Bay of Campeche in the southern Gulf of Mexico. Several recent runs of the ECMWF and GFS models have given support to the idea that a tropical depression would form at the tail end of this front late this week, in Mexico's Bay of Campeche. The path such a storm might take would depend strongly on where the center forms. A more northerly formation location near the top of Mexico's Yucatan Peninsula would likely result in a northward motion towards the Florida Panhandle, while a more southerly formation location might lead to the storm getting trapped in a region of weak steering currents, resulting in a slow, erratic motion in the southern Gulf. NHC is currently not highlighting the Bay of Campeche in their Tropical Weather Outlook, and it will likely be Wednesday before enough heavy thunderstorms build to warrant mention.

Jeff Masters

Fire Hurricane

Updated: 4:45 PM GMT on September 05, 2011

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Lee drenching the Gulf Coast; Katia a Cat 2

By: JeffMasters, 3:31 PM GMT on September 04, 2011

Tropical Storm Lee made landfall on the southern coast of Louisiana near 4 am CDT this morning, and continues to inch slowly northward and dump very heavy rains. The storm is not a threat to intensify, since its center lies over land, but enough of the storm's circulation is over water that Lee will be slow to weaken. At New Orleans Lakefront Airport, 8.85" inches of rain had fallen from Lee as of 9 am CDT this morning. Top winds this morning hit 46 mph, gusting to 57 mph, at 6:28 am CDT, when a heavy squall blew in. Latest satellite loops show Lee has lost quite a bit of its heavy thunderstorms since yesterday, but the storm remains a formidable rain-maker. Lee brought a storm surge of 4 feet to New Canal Station in Lake Pontchartrain and at Shell Beach east of New Orleans yesterday afternoon. NOAA's Storm Prediction Center reported eight probable tornadoes from Lee yesterday. These tornadoes damaged approximately ten buildings, but caused no deaths or injuries.


Figure 1. Observed rainfall for the seven-day period ending at 8 am EDT Sunday Sep 4, 2011. Tropical Storm Lee had dumped 5 -10 inches of rain over a large swath of the coast, with a few areas in excess of ten inches (pink colors). Image credit: NOAA/AHPS.


Figure 2. Predicted rainfall for the 5-day period 8am EDT Sunday - 8 am EDT Friday, Sep 9, 2011. Lee is expected to bring a large swath of 4+ inches of rain all the way to the mid-Atlantic. Image credit: NOAA/HPC.

Forecast for Lee
Lee's large size and slow movement will make heavy rains the main concern today. Later in the week, the remnants of Lee's may be a problem for the mid-Atlantic and Northeast, where recovery efforts from the devastating flooding due to Hurricane Irene may be hampered by an additional 2 - 3 inches of rain. Tornadoes from Lee are a potential hazard today, as NOAA's Storm Prediction Center is highlighting the Northern Gulf Coast in their "slight risk" area for severe weather. A tornado watch is posted for the region, but no tornadoes have been reported as of 9 am CDT.

Hurricane Katia
Hurricane Katia finally overcame the wind shear and dry air interfering with it, and intensified into a Category 2 hurricane with 100 mph winds this morning. Latest satellite loops show a well-defined eye for the first time, but the hurricane still has a lopsided appearance, due to he impacts of dry air and moderate wind shear of 10 - 20 knots on its southwest side.

Katia will not pose a danger to any land areas over the next five days, but may be a threat to the U.S. late this week. The computer models disagree considerably on the position and strength of a trough of low pressure that will develop over the Eastern U.S. late this week, and thus how Katia will be steered. The evolution of this trough will be strongly affected by Tropical Storm Lee, and the models are not very skillful at predicting transitions from tropical storm to extratropical storm, which will happen to Lee by Wednesday this week. We have two of our reliable models--the ECMWF and UKMET--predicting that the trough will form farther west, steering Katia very close to North Carolina late this week. The rest of the models predict a more easterly position of the trough, which would force Katia to turn northwards towards Canada well before reaching North Carolina. Either scenario is possible, and it will probably be at least another day before the models converge on a solution for the long-term fate of Katia. It's likely that locations on the U.S. coast south of North Carolina will not receive a direct hit from Katia, but the entire coast from North Carolina northwards to New England and Canada's Maritime Provinces is definitely at risk. Long period swells from Katia will begin affecting the Bahamas tonight, then reach the Southeast U.S. by Monday morning. By Tuesday morning, the entire U.S. East Coast will see high surf from Katia, and these waves will increase in size and power as the storm grows closer. Given the slow movement of Katia as it approaches the coast, plus its expected Category 1 to 3 strength as it approaches, the storm will probably cause extensive beach erosion and dangerous rip tides for many days.


Figure 3. Morning satellite image of Hurricane Katia.

Elsewhere in the tropics
This week and next week typically mark the two most active weeks of the Atlantic hurricane season, and there are two potential threat areas we need to watch. The GFS model predicts that a tropical depression could form in the southern Gulf of Mexico's Bay of Campeche by Friday or Saturday this week. Several other models give support to this idea, and predict such a storm would track northwards or north-northeastwards towards the northern Gulf Coast between Louisiana and the Florida Panhandle. The other region to watch is between the Lesser Antilles and the coast of Africa. The NOGAPS model is predicting that a tropical wave currently near the coast of Africa could develop into a tropical depression late this week, and arrive in the northern Lesser Antilles by Saturday or Sunday.

Jeff Masters

Hurricane

Updated: 3:37 PM GMT on September 04, 2011

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Tropical Storm Lee lingers off Louisiana coast

By: JeffMasters, 1:16 AM GMT on September 04, 2011

Tropical Storm Lee continues to bring heavy rain, moderately strong wind gusts, and tornado risk to the Gulf Coast states east of Texas. Lee is 55 miles south of Lafayette, Louisiana, and is drifting almost due north at 4 mph. Lee's central pressure dropped to 988 mb since this morning, but has maximum sustained wind speeds that have decreased to 50mph. The National Hurricane Center has extended the tropical storm warning eastward to Destin, Florida. Since this morning, New Orleans Lakefront Airport has received about another inch of rain for a storm total of 6.87 inches. Rainfall estimates from radar suggest some locations, especially close to the coast, might have already seen up to 8 inches of rain from Tropical Storm Lee. Although the New Orleans area is in a dry slot of the storm, more rain can be expected through the night in the form of isolated storms with heavy downpours. Louisiana's Jefferson Parish officials ordered a mandatory evacuation for three towns earlier today: Lafitte, Crown Point, and Barataria. Heavy rain and tidal surge pushed the water of Bayou Barataria into the surrounding low-lying areas, and officials warned that if residents didn't leave, they might become stranded for a couple of days.


Figure 1. Infrared satellite of Tropical Storm Lee captured around 6pm EDT. Source: NOAA.

Forecast for Tropical Storm Lee
Lee's forecast hasn't changed much since this morning. Dry air is being pulled in from the west, which is giving the storm a very subtropical appearance, and is mitigating intensification. Earlier today, two centers of circulation were visible in satellite and confirmed by Hurricane Hunters. The centers were rotating around each other in full Fujiwara fashion, and although they were scientifically interesting, it meant that there was no clear center of circulation, and probably helped to weaken storm. The National Hurricane Center expects that Lee will come ashore in Louisiana later this evening and linger over the region until Monday, when it will finally be pushed north by a mid-latitude wave.

Lee's tornado threat
A tornado watch is in effect for southern Louisiana and portions of Mississippi, Alabama, and the western Florida Panhandle until 10pm CDT. The forecast is for small and short-lived tornadoes, but the threat for tornado damage is still there. A PhD student at Georgia Tech (and my former group member), James Belanger, runs a skillful model to predict the number of tornadoes that a tropical cyclone could produce. The model uses variables such as the size of the storm, the maximum wind speed, and moisture. For the 2008 hurricane season, the model accurately predicted the number of tornadoes that would be spawned from a quite a few tropical cyclones, including Hurricane Dolly, Tropical Storm Edouard, Tropical Storm Fay, and Hurricane Ike. Given today's forecast track and intensity, Belanger's model is forecasting 30-40 tornadoes could be spawned from Tropical Storm Lee, mainly in the Southeast states east of and including Louisiana.

Interestingly, although the nose of dry air that's being pulled in from drought-stricken Texas (visible in the satellite image above) is acting to keep the storm weak, it's also playing a role in the number of tornadoes that could be spawned from Lee. The dry air is a crucial component for the storm to develop discrete, isolated thunderstorm cells (versus a large shield of heavy rain). The discrete cells, just like during severe weather season, are the storms that are most capable of producing a tornado.

Angela

Hurricane

Updated: 1:18 AM GMT on September 04, 2011

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Tropical Storm Lee moving ashore; Katia continues northwest

By: JeffMasters, 1:53 PM GMT on September 03, 2011

Tropical Storm Lee is marching steadily northwards towards landfall in Louisiana, and continues to slowly intensify. The storm's central pressure is now down to 993 mb, as measured by an Air Force hurricane hunter aircraft at 7am CDT. However, the center of Lee is now very close to the coast, and the storm doesn't have much time to intensify further before the center moves over land. The main impact from the storm on the coast thus far has been heavy rains. At New Orleans Lakefront Airport, 5.88" inches of rain had fallen from Lee as of 8 am CDT this morning. Top winds were 35 mph, gusting to 55 mph. Though Lee's top winds are rated as being 60 mph, it is difficult to find any land stations that have reported sustained winds of tropical storm force, 39 mph or greater. One station that has is at the tip of the Mississippi River Delta, where Southwest Pass measured sustained winds of 40 mph, gusting to 58 mph, at 7:03 am CDT. Upper-level winds out of the southwest are creating a moderate 10 - 20 knots of wind shear over Lee, keeping the storm's heavy thunderstorms pushed to the east side of the storm. Latest satelllite loops show Lee is becoming increasingly organized.


Figure 1. Radar-estimated rainfall from Lee from the New Orleans radar. Lee has dumped a large region of 4 - 8 inches so far (orange colors.)


Figure 2. Predicted rainfall for the 5-day period ending at 8 am EDT Thursday Sep 8, 2011. Lee is expected to bring a large swath of 4+ inches of rain all the way to New England. Image credit: NOAA/HPC.

Forecast for Lee
Lee's large size, ill-formed circulation center, and the presence of dry air on its west side due to an upper-level trough of low pressure make Lee look a lot like a subtropical storm on satellite imagery, with a broad center and the majority of the heavy thunderstorms in a broad band well removed from the center. Subtropical storms can undergo only relatively modest rates of intensification, and Lee is unlikely to become a hurricane. Also tending to slow intensification will be the fact that much of its circulation is over land. Damages from Lee are likely to be less than $100 - $200 million, with the greatest threats being fresh water flooding from heavy rains. Given that much of the region Lee will traverse over the next few days is under moderate to severe drought, the storm's rains may cause more economic benefit than damage. Since Texas is on the dry side of the storm, that state will see very little rainfall from Lee, except very close to the border with Louisiana. The rains from Lee appear to have mostly ended across extreme southern Louisiana, so the feared 10 - 15 inches of rain does not look like it will materialize there. One possible concern for Lee's rains will be the mid-Atlantic and Northeast, where recovery efforts from the devastating flooding due to Hurricane Irene may be hampered by the additional 2 - 4 inches that may fall from Lee's remnants by the middle of the week.Tornadoes from Lee are potential hazard today, as NOAA's Storm Prediction Center is highlighting the Northern Gulf Coast in their "slight risk" area for severe weather. A tornado watch is posted for the region, but no tornadoes have been reported as of 8 am CDT.

Lee is the 12th named storm this year, and came eight days before the half-way point of the Atlantic hurricane season. Climatologically, September 10 marks the half-way point. A typical hurricane season has just 10 - 11 named storms, so we've already had more than a whole season's worth of storms before reaching the half-way point. At this rate, 2011 will see 24 - 26 named storms, making it the 2nd busiest season on record, behind 2005. Lee's formation date of September 2 puts 2011 in 5th place for earliest date of arrival of the season's 12th storm. Only 2005, 1995, 1936, and 1933 had an earlier 12th storm.

Hurricane Katia
The latest set of model runs show very little change in the outlook for Hurricane Katia. Katia will continue its long trek across the Atlantic Ocean, and will not pose a danger to any land areas over the next five days. Katia is still struggling with dry air and wind shear that has risen to a high 20 - 25 knots. Latest satellite loops show a lopsided hurricane that is suffering from the impacts of dry air and wind shear on its southwest side.

The models now agree that the upper-level trough of low pressure bringing the wind shear to Katia will move away by Sunday, putting Katia in an environment with low to moderate wind shear. At the same time, ocean temperatures will warm to 29°C, a full 0.5°C over what Katia is experiencing today. These effects should allow Katia to intensify to a Category 2 hurricane by Monday. It is still unclear how much of a threat Katia may pose to the U.S., as this depends on the strength and timing of a trough of low pressure predicted to move off the U.S. East Coast 5 - 7 days from now. Our models do not have enough skill to predict how the steering currents will behave that far into the future. As I mentioned in yesterday's post, part of the problem is due to the inability of the computer models to agree on what will happen to Tropical Storm Talas in the Western Pacific. Talas hit Japan early on Saturday as a strong tropical storm, and is racing northwestwards towards Alaska. Talas is expected to transition into a powerful extratropical storm in the waters south of Alaska early next week. This extratropical storm will create a ripple effect downstream in the jet stream, all the way to North America, affecting the trough of low pressure off the U.S. East Coast expected to potentially recurve Katia when it approaches the U.S. The computer models are not very good at handling these sorts of interactions, leading to more than the usual amount of uncertainty in the long-range outlook for Katia. It will probably be another two days before the models will converge on a solution for the long-term fate of Katia. It's a good bet that locations on the U.S. coast south of North Carolina are in the clear, but residents from North Carolina to New England need to watch Katia. Dr. Bob Hart's Historical Tropical Cyclone Probability web page suggests shows that tropical storms in Katia's current position have a 15% chance of hitting North Carolina, a 22% chance of hitting Canada, a 12% chance of hitting New England, and a 58% chance of never hitting land. One almost certain impact of Katia on the U.S. will be large waves. Long period swells from Katia will begin affecting the Bahamas on Sunday night, then reach the Southeast U.S. by Monday morning. By Tuesday morning, the entire U.S. East Coast will see high surf from Katia, and these waves will increase in size and power as the storm grows closer. Given the slow movement of Katia as it approaches the coast, plus its expected Category 1 to 3 strength as it approaches, the storm will probably cause extensive beach erosion and dangerous rip tides for many days.


Figure 3. Satellite image of Tropical Storm Talas taken September 2, 2011, as the storm approached Japan. Image credit: NASA.

Jeff Masters

Hurricane

Updated: 3:18 PM GMT on September 03, 2011

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TD 13 intensifying; Katia may pass uncomfortably close to U.S.

By: JeffMasters, 3:28 PM GMT on September 02, 2011

Tropical Depression Thirteen formed last night over the Northern Gulf of Mexico and is slowly intensifying, but isn't in a hurry to go anywhere. What TD 13 will do is dump torrential rains along the northern Gulf Coast over the next three or more days. So far, rain amounts along the coast have mostly been below one inch. At New Orleans Lakefront Airport, just 0.32" inches of rain had fallen from TD 13 as of 10 am CDT. Some coastal regions have received up to two inches, according to radar rainfall estimates. TD 13 is generating a large area of 30 - 35 mph winds over the Gulf of Mexico. At 7:20 am CDT, winds at the Mississippi Canyon 711 oil rig were southeast at 47 mph. This is above tropical storm force, but the wind instrument was 348 feet (106 m) above the ocean surface, and winds near the surface were probably considerably lower, near 35 mph. Latest surface wind observations from an Air Force hurricane hunter aircraft support leaving TD 13 as a tropical depression. Long range radar out of Mobile, Alabama shows heavy rain showers building along the northern Gulf Coast, but these rain showers are not well-organized into spiral bands. Strong upper-level winds out of the west-northwest are creating a moderate 10 - 20 knots of wind shear over TD 13, keeping the storm's heavy thunderstorms disorganized and pushed to the east side of the storm. However, latest satelllite loops show TD 13 is becoming increasingly organized, with a respectable spiral band forming on the southeast side, and an increase and areal coverage of heavy thunderstorm activity. This is very likely to be a tropical storm later today.


Figure 1. Radar-estimated rainfall from TD 13 from the New Orleans radar.


Figure 2. U.S. drought conditions on August 30. The rains from TD 13 have the potential to bring major drought relief to drought-stricken portions of the coast. Note how Eastern North Carolina is no longer in drought, thanks to the rains from Hurricane Irene. These rains also came close to putting out a persistent fire that had been burning in the Great Dismal Swamp near the Virginia/North Carolina border. Image Credit: U.S. Drought Monitor.

Forecast for TD 13
TD 13's large size, ill-formed circulation center, and the presence of dry air on its west side due to an upper-level trough of low pressure argue against rapid intensification of the storm for the next three days. Also tending to slow intensification will be the slow movement of the storm, which will allow cold water from the depths to rise to the surface, thanks to wind and wave action. Tropical cyclones strongly cool the water's surface when they pass over it, as seen in the time vs. depth chart of sea surface temperatures during Hurricane Irene's passage along the New Jersey coast (Figure 3.) However, the Gulf of Mexico has some very warm waters near TD 13 that extend to great depth (Figure 4), so the surface cooling imparted by TD 13 will be less than that seen for Hurricane Irene. As TD 13 moves closer to the coast, more and more of its circulation will be over land, which will also slow intensification. NHC's 11 am EDT wind probability forecast for TD 13 gave the storm a 23% chance of intensifying into a hurricane by Sunday. Assuming TD 13 does not attain hurricane strength, wind damage and storm surge damage will likely not be the main concern--fresh water flooding from heavy rains will be the most dangerous impact. Also of concern is the possibility of tornadoes. NOAA's Storm Prediction Center is currently not highlighting the Gulf Coast in their "slight risk" area for severe weather, due to the lack of enough solar heating to create instability. However, there will be plenty of wind shear in the lower part of the atmosphere that can potentially create spin in the coastal thunderstorms, and it is possible that as TD 13 intensifies, it may be able to generate several dozen tornadoes.

Coastal Louisiana, Mississippi, Alabama, and the extreme western Panhandle of Florida will likely receive very heavy flooding rains that will intensify Saturday and peak on Sunday. These rains should be able to put out the stubborn marsh fire east of New Orleans that has brought several days of air quality alerts to the city, but may cause moderate to severe flooding problems in other areas. The latest rainfall forecast from NOAA Hydrological Prediction Center shows that a large area of 15+ inches of rain is expected over Southeast Louisiana and coastal Mississippi. The region is under moderate drought, so flooding problems will be delayed compared to what we'd normally expect from heavy rains of over a foot. Flash flood watches are posted for New Orleans and surrounding areas, and rainfall amounts of 1 - 3 inches per hour are possible in some of the heavier rain squalls. Ocean temperatures are near record warmth, 88°F (31°C), which will provide plenty of moisture for heavy rains, and plenty of energy to help TD 13 strengthen into a strong tropical storm. Steering currents will be weak in the Gulf this weekend and early next week, which will likely make the motion of TD 13 erratic at times.


Figure 3. EPA, in conjunction with Rutgers University and the NJ Department of Environmental Protection, has an Autonomous Underwater Vehicle (AUV, aka the Glider) deployed off the coast of NJ (since early August) continuously monitoring ocean temperature, density, salinity, sound velocity and dissolved oxygen at different depths. The AUV's path and data are displayed at the following website: http://marine.rutgers.edu/cool/auvs/index.php?did =221&view=imagery. The plot of temperature versus time above shows that in the weeks prior to the arrival of Irene, the ocean was heavily stratified, with warm waters of 24 - 26°C (75 - 79°F, red colors) extending from the surface to a depth of 10 - 15 meters. A sharp thermocline existed at a depth of about 15 meters, and ocean temperatures were colder than 14°C (57°F, dark blue colors) below the thermocline. The strong winds and high wave action of Hurricane Irene on August 28 - 29 stirred up cold water from the depths to the surface, cooling the surface waters to 17 - 19°C (63 - 67°F). In the days since the hurricane, surface waters have begun to warm again. Thanks go to Kevin Kubik, Deputy Director of the Division of Environmental Science and Assessment for EPA Region 2, for making me aware of this data.


Figure 4. The total amount of heat energy in the ocean available to fuel a tropical cyclone, in kilojoules per square centimeter of surface area. Tropical cyclones that move over ocean areas with TCHP values in excess of 70 - 90 kJ/cm^2 commonly undergo rapid intensification. Waters that are warm to a great depth have the highest TCHP, and the Loop Current that brings warm water northwards from the Caribbean to the Gulf of Mexico usually has the highest TCHP values in the Atlantic. Currently, we have an eddy that broke off from the Loop Current earlier this summer, now located a few hundred miles south of the Louisiana coast, that also has high TCHP values. Image Credit: NOAA/AOML.

Hurricane Katia
Hurricane Katia is continuing its long trek across the Atlantic Ocean today, and will not pose a danger to any land areas over the next five days. Katia is still struggling with dry air and moderate wind shear of 10 - 20 knots. Latest satellite loops show surface-based arc-shaped clouds racing to the southwest away from Katia's core, a sign that dry air is penetrating into Katia's thunderstorms and creating strong downdrafts that are robbing the storm of heat and moisture. Katia is over warm ocean waters of 28.5°C, and these waters will increase in temperature to 29°C over the next five days. Katia will pass well north of the region of cooler waters stirred up by the passage of Hurricane Irene last week.

The models are split on when the upper-level trough of low pressure bringing the wind shear to Katia will move away, and the storm may spend two more days battling wind shear and dry air before the upper-level trough pulls away to the north and allows Katia to intensify more readily. It is still unclear how much of a threat Katia may pose to the U.S., but it is becoming increasingly clear that Katia will pass uncomfortably close to the U.S. East Coast. The trough of low pressure currently steering Katia to the northwest will lift out early next week, and a ridge of high pressure is expected to build in, forcing Katia more to the west. This decreases the danger to Bermuda, but increases the danger to the U.S. A second trough of low pressure is expected to begin affecting Katia by the middle of next week, and will potentially recurve the storm out to sea before it hits the U.S. However, the models differ widely on the strength and timing of this trough. Meteorologist Grant Elliot of Australia's Bureau of Meteorology in Perth pointed out to me yesterday that the long-range forecast for Katia has more than the usual amount of uncertainty, due to the inability of the computer models to agree on what will happen to Tropical Storm Talas in the Western Pacific. Talas is expected to hit Japan early on Saturday as a strong tropical storm, then race northwestwards into the Bering Sea off the coast of Alaska. Talas is then expected to transition into a powerful extratropical storm in the waters south of Alaska. This storm will create a ripple effect downstream in the jet stream, all the way to North America, by early next week. The timing and amplitude of the trough of low pressure off the U.S. East Coast expected to potentially recurve Katia out to sea next week is highly dependent upon the strength of Tropical Storm Talas during its transition to an extratropical storm. The computer models are not very good at handling these sorts of transitions, leading to more than the usual amount of uncertainty in the long-range outlook for Katia. It will probably be another 2 - 3 days before the models will begin to converge on a solution for the long-term fate of Katia. Dr. Bob Hart's Historical Tropical Cyclone Probability web page suggests shows that tropical storms in Katia's current position have a 17% chance of hitting North Carolina, a 21% chance of hitting Canada, a 13% chance of hitting New England, and a 55% chance of never hitting land. One almost certain impact of Katia on the U.S. will be large waves. Long period swells from Katia will begin affecting the Bahamas on Sunday night, then reach the Southeast U.S. by Monday morning. By Tuesday morning, the entire U.S. East Coast will see high surf from Katia, and these waves will increase in size and power as the storm grows closer. Given the slow movement of Katia as it approaches the coast, plus its expected Category 1 to 3 strength as it approaches, the storm will probably cause extensive beach erosion and dangerous rip tides for many days.

94L
A well-organized low pressure system with a surface circulation but limited heavy thunderstorm activity due to high wind shear is 450 miles south of Halifax, Canada. This disturbance, (94L), is headed northeast out to sea, and is being given a 60% chance of developing into a tropical depression by NHC. 94L is under a high 25 - 30 knots of wind shear, but this shear is expected to fall to the moderate range, 10 - 20 knots, by Saturday morning. However, sea surface temperature will fall from 27°C today to 25°C Saturday morning underneath 94L, and the storm will have a very short window of time to get organized enough to get a name. At this point, it's really a subjective judgement call on whether or not 94L is already a tropical storm.


Figure 5. A Portlight volunteer works to clear storm debris from Hurricane Irene in Hollywood, Maryland.

Portlight disaster relief effort in Maryland
Hurricane Irene heavily damaged the town of Hollywood, Maryland, when a tornado cut off electric power, water, and phone service. Portlight and Team Rubicon volunteers arrived before emergency personnel, after following up on a local tip. What they found was an isolated area whose plight was unknown to the larger community. Most residents were trapped at their homes by heavy debris. Portlight and Team Rubicon worked for two days to clear paths to each address, extract vehicles from debris, and cut down trees that constituted safety hazards. Portlight also instructed local residents how to operate and maintain chainsaws and safely clear debris. No other volunteer organizations or emergency personnel arrived at any time, and Portlight succeeded in meeting the specific needs of the underserved, unserved, and forgotten. Visit the Portlight blog to learn more; donations are always welcome.

I'll have a new post each morning over the coming holiday weekend; wunderground meteorologists Angela Fritz, Rob Carver, and Shaun Tanner will be handling the afternoon and evening posts. Have a great holiday weekend, everyone!

Jeff Masters

Hurricane

Updated: 5:25 PM GMT on January 09, 2012

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Tropical Depression Thirteen Forms in The Gulf of Mexico

By: JeffMasters, 4:59 AM GMT on September 02, 2011

Tropical Depression Thirteen

As has been predicted by the major models this week, the broad area of disturbed weather that began in the western Caribbean Sea and meandered into the Gulf of Mexico has developed into Tropical Depression Thirteen. The most recent satellite image of the depression from 11:00 p.m. CDT (Figure 1) shows deep convection mainly confined to east of center, but westerly shear of 20 knots is expected to relax over the 24 hours. While this relaxation, in combination with sea surface temperatures well above the threshold for intensification, should lead to some strengthening, the sheer size of the depression would require significant time for the system to become a hurricane.


Figure 1: Infrared image of Tropical Depression Thirteen. The depression is centered south of Louisiana and is expected to move very slowly toward the coast over the next few days.

Track of Tropical Depression Thirteen

The depression's center position is still quite uncertain, as is the overall track. We should get a better idea of what is going on inside of the depression, along with pinpointing its center, after a couple of hurricane hunter aircraft complete their investigation over the next 12-24 hours.

The initial track, although uncertain, strengthens the depression into a tropical storm (which would be named Lee) on Friday while curving to the northwest. After Friday, it is possible that the system would gradually turn to the northeast, making landfall along the coast of Louisiana Sunday evening. It is important to note, however, that the track is uncertain at this time and could vary over the next few days. The depression is currently south of a high pressure ridge that is not giving much in the way of steering currents. This is also the reason for its very slow movement.


Figure 2: 5-day forecast map of Tropical Depression Thirteen.


Effects of Tropical Depression Thirteen

Tropical Storm Warnings have already been posted for the central Gulf Coast due to its proximity to the area. At this time, hurricane force winds are not expected for the area, but because the depression/tropical storm will be slow-moving, it may be a large precipitation-producer throughout the Southeast. You can already see rain from the northernmost part of the depression on radar out of New Orleans. Southern Louisiana through southern Alabama is set to receive 10-15 inches of rain, while higher amounts near 20 inches are possible in the hardest hit areas. This could lead to a precipitation pattern much like Hurricane Danny in 1997, except peak areas would receive less rain. Unfortunately for Texas, the major models are not currently producing any rain in the drought-stricken state, aside from areas bordering Louisiana. But, Tropical Depression Thirteen is likely to aid drought conditions in other parts of the Southeast, including Louisiana. (Figure 5).



Figure 3: Tropical Storm Warnings have been posted for the central Gulf Coast.


Figure 4. Rainfall amounts from Hurricane Danny July 17-26 1997. Note the astonishing 37.755 inches recorded at Dauphin Island, AL.


Figure 5. Drought Monitor image from August 30 showing exceptional drought conditions through much of Texas and parts of Louisiana.

We will be monitoring this storm as it moves slowly through the northern Gulf of Mexico over the next few days. You can also follow us on Twitter (@wunderground) and on Facebook for the latest developments.

Dr. Masters will be back in the morning with another blog highlighting the latest with Tropical Depression Thirteen.


Thanks for reading,

Shaun Tanner

Updated: 5:05 AM GMT on September 02, 2011

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Gulf of Mexico disturbance 93L a Lousiana flood threat; Katia a hurricane

By: JeffMasters, 3:28 PM GMT on September 01, 2011

Surface winds over the northern Gulf of Mexico are rising, pressures are falling, and heavy thunderstorms are building today thanks to a tropical disturbance (Invest 93L) that is the product of a tropical wave interacting with an upper-level low pressure system. At 8:35 am CDT, winds at the Mississippi Canyon 711 oil rig were south-southeast at 38 mph. This is just 1 mph below tropical storm force, but the wind instrument was 348 feet (106 m) above the ocean surface, and winds near the surface were probably considerably lower, near 30 mph. Long range radar out of Mobile, Alabama shows heavy rain showers building along the northern Gulf Coast, but these rain showers are not organized into spiral bands and show no signs of rotation. Strong upper-level winds out of the west-northwest are creating 30 knots of wind shear over 93L, keeping the storm's heavy thunderstorms disorganized. Strong onshore winds raising tides to 1 - 2 feet above normal are likely along the northern Gulf Coast through the weekend, and coastal flood statements have been issued for the region.


Figure 1. Predicted rainfall for the 5-day period ending at 8am EDT Sep 6, 2011. A large region of rains in excess of 15 inches is expected over Southeast Louisiana. Image credit: NOAA/HPC.


Figure 2. U.S. drought conditions on August 30. The rains from 93L have the potential to bring major drought relief to drought-stricken portions of the coast. Image Credit: U.S. Drought Monitor.

By late tonight, wind shear is expected to drop to the moderate range, below 20 knots, and 93L should begin to organize into a tropical depression. Wind shear is expected to remain moderate, 10 - 20 knots, into Monday. There is some cold, dry air aloft that will retard this process, and I think the earliest we would see a tropical depression is Friday afternoon. NHC is giving 93L a 70% chance of developing into a tropical depression by Saturday morning. All of the major models develop 93L near the Louisiana coast, and show a slow and erratic movement due to weak steering currents. Coastal Louisiana, Mississippi, Alabama, and the extreme western Panhandle of Florida will likely receive very heavy flooding rains beginning this afternoon and intensifying Friday and Saturday. The latest rainfall forecast from NOAA Hydrological Prediction Center (Figure 1) shows that a large area of 15+ inches of rain is expected over Southeast Louisiana. The region is under moderate drought, so flooding problems will be delayed compared to what we'd normally expect from heavy rains of over a foot. Nevertheless, minor to moderate freshwater flooding is likely from 93L, and flash flood watches are posted for New Orleans and surrounding areas, and rainfall amounts of 1 - 3 inches per hour are possible in some of the heavier rain squalls. Ocean temperatures are near record warmth, 88°F (31.3°C), which will provide plenty of moisture for heavy rains, and plenty of energy to help 93L strengthen into a tropical storm. Most of the models predict 93L will have some motion to the west by Saturday, which would bring rains to the Texas coast near the Louisiana border. Steering currents will be weak in the Gulf this weekend and early next week, making it difficult to predict where the storm might go. If 93L stays over water through Tuesday, like the ECMWF model is predicting, the storm would be a threat to intensify into a hurricane. Most of the other models predict 93L will move ashore over Louisiana by Sunday, limiting the storm's development to just tropical storm strength. I think it at least 50% likely 93L will be a tropical storm with 40 - 60 mph winds along the coast of Louisiana by Sunday.

Hurricane Katia
Hurricane Katia intensified into the 2nd hurricane of the 2011 season last night, and continues its long trek across the Atlantic Ocean today. Katia is expected to arrive at a position several hundred miles north of the Northern Lesser Antilles Islands by Monday. The islands are not in the cone of uncertainty, and it appears unlikely that they will receive tropical storm-force winds from Katia. Satellite images show that Katia is a well-organized storm with plenty of heavy thunderstorms, but the storm has been struggling with dry air and moderate wind shear of 10 -20 knots, and is looking less organized than it did last night. These problems will likely diminish by Friday night, as the upper low bringing the wind shear moves away. It is still unclear how much of a threat Katia may post to the U.S. Dr. Bob Hart's Historical Tropical Cyclone Probability web page suggests shows that tropical storms in Katia's current position have an 16% chance of hitting North Carolina, a 21% chance of hitting Canada, a 12% chance of hitting Florida, and a 54% chance of never hitting land. I suspect that Katia will turn north before reaching the U.S. and potentially threaten Bermuda and Canada, based on what past storms in similar situations have done, and assuming the jet stream maintains its current pattern of bringing frequent troughs of low pressure off the coast of the U.S. It will be another day or two before the models will begin to have a handle on the long-term fate of Katia, though.


Figure 3. Morning satellite image of Katia.

94L
A well-organized low pressure system with a surface circulation and limited heavy thunderstorm activity has developed between Bermuda and the Canadian Maritimes. This disturbance, (94L), is headed out to sea, and is being given a 10% chance of developing into a tropical depression by NHC. 94L is under a very high 30 - 40 knots of wind shear, and will not be able to intensify very much. However, Tropical Storm Jose formed from a similar type of system, and we might get surprised by 94L.

I'll have more on Irene in tomorrow's post.

Jeff Masters

Hurricane

Updated: 3:29 PM GMT on September 01, 2011

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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.