Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 2:05 PM GMT on September 18, 2007
An area of disturbed weather has developed off the east coast of Florida, in association with a tropical wave interacting with a trough of low pressure. This disturbance has been labeled "93L" by NHC this afternoon. Animations of long-range radar out of Melbourne, Florida and satellite loops show that thunderstorm activity off the Florida coast is increasing, but remains disorganized. Wind shear over the disturbance has fallen from 30 knots to 20 knots today, and is expected to fall below 10 knots by Thursday. The disturbance is moving westward, and will bring heavy rain to Florida and the Bahamas today through Thursday.
Figure 1. Current long range radar out of Melbourne, Florida.
The four reliable computer models for forecasting tropical cyclone genesis all predict that once this area of disturbed weather crosses Florida and emerges into the eastern Gulf of Mexico on Thursday, wind shear will drop enough to allow a tropical depression to form. The path such a storm might take is highly uncertain, and the models have diverged significantly since yesterday's runs. A strong ridge of high pressure is setting up over the eastern half of the U.S., and is expected to remain anchored in place for at least ten days. This is the type of steering pattern we experienced during the Hurricane Season of 2005, and favors westward-moving storms. This ridge will act to steer any developing storm in the Gulf of Mexico towards the west, to the Texas coast, or even west-southwest, to the northeastern mainland Mexico. However, this steering pattern will be complicated by the presence of an upper-level low pressure system over the Gulf of Mexico. This upper-level low is currently forming over northern Florida, and is expected to drift southwestward or westward over the Gulf later this week, and gradually weaken. Depending on the strength and movement of this low, a storm that forms in the eastern Gulf could be steered anywhere from the Florida Panhandle to northeastern Mexico. One model, the NOGAPS, predicts that the storm will move west-southwest into the Bay of Campeche (southwestern Gulf of Mexico), and stall out for many days. The UKMET, GFS, and ECMFW models foresee that the storm will make landfall in Texas or Louisiana Sunday or Monday. The intensity such a storm may reach is also highly uncertain. The NOGAPS model predicts 93L will eventually dissipate over the southwestern Gulf, while the SHIPS intensity model brings 93L to Category 1 hurricane strength by Saturday. All residents along the Gulf of Mexico coast need to consider what actions they might need to take if a hurricane develops in the Gulf this weekend. The highest danger region is from New Orleans westward to Brownsville, Texas. A hurricane hunter airplane is on call for Thursday afternoon.
Remains of Ingrid
The remains of Tropical Storm Ingrid are still kicking up some heavy thunderstorm activity a few hundred miles north of the northernmost Lesser Antilles Islands. There is still a bit a spin evident on satellite loops and this morning's QuikSCAT pass. Wind shear is a hefty 30 knots, and is expected to gradually decline to 10 knots by Wednesday night. If there's anything left of Ingrid then, we will need to watch this area for regeneration.
Tropical wave in the mid-Atlantic
A tropical wave about 750 miles east of the Lesser Antilles Islands is moving west at 10-15 mph. Thunderstorm activity associated with this wave has diminished substantially since yesterday, and any development should be very slow to occur. Wind shear is about 10 knots, and is expected to remain below 15 knots over the next 2-3 days. None of the computer models develop this wave into a tropical depression.
Typhoon Wipha takes aim at China's most populous city
Typhoon Wipha, a formidable Category 4 storm, is poised to make landfall tomorrow just south of China's most populous city, Shanghai. About 14.5 million people live in the city. Over 1 million people have been evacuated so far. Wipha must pass over about 50 miles of land before reaching Shanghai, and will probably be a strong tropical storm or Category 1 hurricane when it passes over or just west of the city. Rainfall amounts of up to seven inches in 24 hours are expected along the path of Wipha, which will cause major flooding problems. Fujian province on China's southeastern coast has sent out 1.41 million text messages to warn the public of the upcoming typhoon, the local flood control headquarters said. The Women's World Cup soccer tournament is going on in China, and the U.S. is supposed to play their final group game tomorrow in Shanghai (8pm Tuesday night China time, 8am EST). World Cup organizers are trying to change the game time to get the game in (and then the teams out of Shanghai) before the storm hits.
Yesterday, Wipha briefly intensified into a super typhoon packing 150 mph winds as it brushed Taiwan. One person was killed there. Wipha is a woman's name in the Thai language.
Figure 2. Radar images of Typhoon Wipha as it passed north of Taiwan. Image credit: Taiwan Central Weather Bureau.
Due to popular request, I'll present a wind shear tutorial in Wednesday's blog.
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