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 , 8:10 PM GMT on August 19, 2008
Tropical Storm Fay (AKA "The Joker") is pulling a trick that may be unprecedented--significantly intensifying over land, developing a full eyewall. The radar and satellite images of Fay this afternoon (Figures 1 and 2) show a much better-organized storm than the Fay that made landfall this morning. Fay now has a symmetric appearance with a full eyewall, and the winds near the center were sustained at 60 mph this afternoon at Lake Okeechobee. These winds are higher than anything measured at landfall this morning. Remarkably, the pressure has fallen over 10 mb since landfall, and I can't ever recall seeing such a large pressure fall while a storm was over land. Hurricane Andrew of 1992 crossed South Florida and did not weaken significantly, but "The Joker" has significantly intensified. It does happen sometimes that the increased friction over land can briefly act to intensify a hurricane vortex, but this effect is short-lived, once the storm is cut off from its oceanic moisture source. To have a storm intensify over land and maintain that increased intensity while over land for 12 hours is hard to explain. The only thing I can think is that recent rains in Florida have formed large areas of standing water that the storm is feeding off of. Fay is also probably pulling moisture from Lake Okeechobee. Anyone want to write a Ph.D. thesis on this case? Wow.
Figure 1. What's wrong with this picture? Radar image of Fay over Lake Okeechobee.
Figure 2. What's wrong with this picture, too? Satellite image of Fay over Lake Okeechobee. Fay has a distinct eye on both satellite imagery and radar.
Where will Fay go next?
The computer models are now in better agreement that Fay will emerge over the Atlantic Ocean on Wednesday, and re-intensify. Given the remarkable ability of Fay to intensify over land, I am more of a believer that Fay could become a hurricane over the Atlantic, as forecast by the GFDL and HWRF models. However, the SHIPS intensity model keeps Fay below hurricane strength, and the very slow motion of the storm while over the ocean will likely stir up cold water from the depths, significantly hampering intensification. Wind shear is expected to be 10-20 knots Thursday and Friday, which should prevent rapid intensification, but allow slow to modest intensification. After stalling out off the coast, all of the models agree that a ridge of high pressure will build back in, forcing Fay to the west over northern Florida or southern Georgia. I continue to support a 60% chance that this turn will occur far enough south that Fay will emerge into the northern Gulf of Mexico early next week, and re-intensify.
Links to follow
Wundermap for Central Florida
Elsewhere in the tropics
A tropical wave about 100 0miles west-southwest of the Cape Verde Islands has changed little today. This system (94L) shows signs of rotation on visible satellite imagery. Wind shear is a modest 10 knots over this disturbance, and is expected to remain about 10 knots through Wednesday. The storm is over warm 28°C waters. Given these moderately favorable conditions, NHC is giving this system a medium (20%-50% chance) of developing into a tropical depression by Thursday afternoon. The storm is expected to track west-northwest and be near the northern Lesser Antilles Islands by Friday night. The wind shear forecast has been flip-flopping from low to high and back to low again over the past two days, so I will cautiously forecast some slow development over the next few days, assuming that the current forecast of 10-15 knots will hold over the next 3-5 days. There is a large area of dry air and Saharan dust to the northwest of the storm, as seen on water vapor satellite imagery. This dry air is already interfering with development, and likely will continue to do so over the next three days. The GFDL and HWRF develop 94L into a weak tropical storm.
The next blog will be Wednesday, and may not be until the afternoon. I may have one of the other wunderground meteorologists fill in for me for tomorrow's first blog, then jump in Wednesday evening if Fay looks dangerous.
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