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Fay crosses into Florida Straits and intensifies

By: Dr. Jeff Masters, 1:09 PM GMT on August 18, 2008

Tropical Storm Fay has moved off the coast of Cuba into the Florida Straits, and is already picking up strength. The latest Hurricane Hunter mission found a large area of 50-60 mph winds in the heavy thunderstorm activity over the Florida Straights, between 8-9 am EDT. Long-range radar out of Key West shows the center of Fay's rotation right on the north coast of Cuba, south-southeast of Key West. The radar signature of the storm shows plenty of spiral bands bringing heavy rain (Figure 1), but these bands are not well-organized yet. Visible satellite loops show that Fay has no eyewall yet, and it will not be until late tonight that the storm can build an eyewall and intensify to a Category 1 hurricane. The upper-level anticyclone that was on top of Fay is now to the south of the storm, which means that the clockwise circulation of air around this anticyclone is bringing about 10-15 knots of wind shear from the southwest over Fay. Wind shear of 10-15 knots is expected to continue over Fay until the storm makes landfall on the west coast of Florida. This amount of wind shear usually means only modest intensification can occur, and we should not see a repeat of Hurricane Charley's rapid intensification.

Figure 1. Latest radar-estimated precipitation for Fay.

Impact on the Florida Keys and South Florida
Winds are steadily increasing throughout the Keys, with sustained winds of 28 mph reported at Sombrero Key at 7 am EDT. The Wundermap for the Florida Keys is a good way to look at all the latest wind reports for the region. Wind gusts in excess of hurricane force are possible this afternoon in the Keys as the center of an intensifying Fay roars through the Upper Keys. Over the Miami metro area, winds will gust above tropical storm force, but it will be the rain, not the wind, that will cause the most trouble. Rainfall estimated by the Key West radar (Figure 1) is already at 5+ inches over the Florida Straights, and this heavy rain will be moving over South Florida today, causing extensive freshwater flooding. Southeast Florida is vulnerable to freshwater flooding damage--Hurricane Irene of 1999 dumped 10-20 inches of rain on the Miami area, causing $600 million in damage. Storm surge will not be a major concern in the Keys or Southeast Florida, with only a 2-3 foot storm surge likely in the Keys, and 1-2 feet in Southeast Florida.

Impact on the west coast of Florida
Fay's primary havoc will occur on the west coast of Florida, but it is too early to be confident where the storm might come ashore. Fay's expected track nearly parallel to the shore will mean that slight deviations in the path will result in large changes in where the eye comes ashore. Storm surge will be a major concern to the region just to the right of where the center comes ashore. As I discussed in great detail in last night's blog, the Tampa Bay area is highly vulnerable to storm surge, and can expect maximum surges from a Category 1 hurricane of 6-9 feet, with an additional 1-2 if the storm hits near high tide. Storm surge is also a major concern along all of Southwest Florida, including Fort Myers, Naples, and Venice. For the Naples region, a Category 1 hurricane can generate storm surges of 4-8 feet (Figure 2). Fort Myers is also highly vulnerable to storm surge (Figure 3).

The computer models continue to show and unusual amount of disagreement. The outliers in the 8 pm EDT runs continue to be the NOGAPS and UKMET models, which continue to forecast a landfall on the mid-Florida Panhandle or Big Bend area of Florida. In contrast, the 2 am EDT run of the GFS model is doing what the ECMWF model was doing yesterday--taking Fay across central Florida into the Atlantic, then bringing it back across the state from east to west, then into the Panhandle, resulting in a triple hit on Florida. Although these solutions are outliers, we cannot dismiss them. The latest 2 am EDT HWRF model run has moved considerably further south, bringing Fay ashore near Fort Myers as a 70-75 mph storm with a 977 mb pressure. The latest GFDL is almost identical, bringing a 75-80 mph Category 1 hurricane with a 977 mb pressure ashore near Fort Myers. Both models then anticipate a possible threat to South Carolina later in the week after Fay crosses Florida and emerges in the Atlantic. Right now, the best guess is that Fay will hit the coast between Naples and Sarasota, largely sparing the Tampa Bay region.

Links to follow
Wundermap for the Florida Keys
Key West, FL weather
Miami, Fl weather
Naples, FL weather

Figure 2. Worst-probable storm tide inundation (inundation from storm surge plus an adjustment for the mean high tide that occurs in the Naples area). The colors scale to various Category hurricanes--1, 2, 3, 4, and 5. The map was compiled using data from NOAA's SLOSH model. Image credit: floridadisaster.org.

Figure 3. Worst-probable storm tide inundation (inundation from storm surge plus adjustment for the mean high tide that occurs in the Fort Myers area). The colors scale to various Category hurricanes--1, 2, 3, 4, and 5. The map was compiled using data from NOAA's SLOSH model. Image credit: floridadisaster.org.

Elsewhere in the tropics
The UKMET model is suggesting development of a tropical wave currently located off the coast of Africa, about 600 miles west-southwest of the Cape Verde Islands. This system (94L) is expected to track west-northwest and be near the Lesser Antilles Islands on Saturday. Wind shear is a low 5-10 knots over this disturbance, and some slow development is likely over the next two days.

I'll have updates throughout the day.

Jeff Masters

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

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