Fay chugs on; potentially dangerous disturbance 94L approaches Lesser Antilles

By: Dr. Jeff Masters , 9:23 PM GMT on August 22, 2008

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Tropical Storm Fay continues its leisurely tour of Florida, chugging slowly westward along the northern Gulf Coast. Radar and satellite loops show no major changes to Fay. The storm still has a large circulation with plenty of rain bands sprawling over much of northern Florida and southern Georgia. Fay is headed towards the waters of the extreme northern Gulf or Mexico near the Big Bend region of Florida, and should be able to pull in enough moisture from the Gulf to at least maintain its current strength through Sunday. Fay may be able to intensify to a 50-55 mph tropical storm, but I don't see it reaching hurricane strength, due to the close proximity of the storm to land.

Fay's rains
Fay has brought the Melbourne, Florida region its greatest single-storm rainfall on record. By 1 am EDT today, Fay had dumped 22.83" of rain on Cape Canaveral. The previous rainfall record for a tropical cyclone in the region was set in 1950, when Hurricane King dumped 15.44" of rain on Patrick Air Force Base near Cape Canaveral. Hurricane Wilma of 2005 holds third place--it dumped 13.26" on Kennedy Space Center.

Fay is also one of Florida's rainiest storms on record. According to Wikipedia and NOAA, the eleven rainiest Florida tropical cyclones of all time were:

Easy (1950) 38.70" Yankeetown
Georges (1998) 38.46" Munson
Unnamed (1941) 35.00" Trenton
Dennis (1981) 25.56" Homestead
TD 1A (1992) 25.00" Arcadia Tower
Jeanne (1980) 24.98" Key West
Dora (1964) 23.73" Mayo
TD (1969) 23.40" Havana
Unnamed (1924) 23.22" Marco Island
Bob (1985) 21.50" Everglades City
Alberto (1994) 21.38 Niceville

According to the latest public information statement from the NWS office in Melbourne, we have an unofficial public observation at Melbourne/Windover Farms (through 6 am 8/22/08) of 26.65". If verified, that would make Fay the 4th rainiest Florida tropical cyclone on record.

Rainfall over the Melbourne area will continue Saturday, but should gradually diminish as Fay moves away from the area.


Figure 1. Satellite image of Fay stalled out over the Melbourne, Florida region at 2:35 pm EDT Wednesday, August 20, 2008. Image credit: NASA Earth Observatory.

Links to follow
Wundermap for Central Florida
Tallahassee, FL radar

Disturbance 94L approaching the Lesser Antilles
Heavy thunderstorms associated with a tropical wave (94L) near 11N, 54W, about 500 miles east of the Lesser Antilles Islands, have grown more concentrated in recent hours. This disturbance could be trouble, and bears careful scrutiny. This morning's QuikSCAT pass mostly missed 94L, but did show a pronounced wind shift at the western edge of the disturbance. Visible satellite loops show some evidence of rotation and increase in heavy thunderstorms, but I'm also seeing surface outflow boundaries to the southeast, indicating that dry is getting sucked into the thunderstorms and creating downdrafts that rob the disturbance of energy. Wind shear has fallen to a modest 10 knots over 94L, and the dry air surrounding it has been steadily moistening. Wind shear is expected to drop to a low 5 knots and remain low for the next four days, and NHC is giving this system a medium (20%-50% chance) of developing into a tropical depression by Sunday afternoon. I would put the odds at 40%-70%. Three of our reliable computer models develop the storm. It's easy to see why--the wind shear forecast for the Caribbean calls for very low values of wind shear below 5 knots for most of the coming week (Figure 2). The GFDL calls for 94L to develop into a Category 2 hurricane that threatens Jamaica on Tuesday. The HWRF doesn't develop 94L at all, and the ECMWF and NOGAPS models call for 94L to eventually develop late next week after it moves north of Hispaniola, into the Bahama Islands. All of these models used the wrong starting position of 94L, since the storm re-formed 150 miles to the east of where the models were expecting it to be. Thus, we can put little faith in the details of forecast track of 94L predicted by the models. A track through the Caribbean towards Jamaica currently appears to be the highest probability track to me. Residents of the Lesser Antilles can expect heavy rain and 40 mph wind gusts from 94L when it blows through Saturday and Sunday. Residents of the Dominican Republic, Haiti, and Jamaica should keep a careful eye on this potentially dangerous disturbance.


Figure 2. Wind shear forecast for the Atlantic for 2 am EDT Monday August 25 2008, as predicted by this morning's 2 am EDT run of the GFS model. Very low values of winds shear (red colors) are predicted for the entire Caribbean and Gulf of Mexico. Winds shear values less than 8 m/s (approximately 16 knots, the three red colors) are conducive for tropical storm formation.

Disturbance 95L in the middle Atlantic
Another tropical wave (95L), near 19N 41W, halfway between Africa and the Lesser Antilles Islands, remains disorganized. This morning's QuikSCAT pass showed only a slight wind shift associated with 95L , and no closed circulation. Top winds were about 30 mph. Wind shear is a modest 10 knots over 95L, and is forecast to remain near 10 knots for the next five days. Visible satellite loops show only a small clump of heavy thunderstorm activity, and NHC has downgraded 95L's chance of developing into a tropical depression in the next two days to low (<20% chance).

My next blog will be Saturday.

Jeff Masters

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

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