Fickle Fay

Posted at 7:08 AM on August 21, 2008 by Paul Huttner (1 Comments)

Fay batters Florida

Call her Fickle Fay, the storm that won't go away.

Advisory

NHC track

Discussion

Radar loop

Models

Fay has confounded forecasters and computer models this week. Her development was irregular with convection largely confined to the east side of the center as the storm was near Cuba. As the upper level wind shear decreased, Fay became more concentric as it made a run at the Florida Keys Monday.

Then Fay did something most tropical cyclones don't do. It strengthened after land fall. There are 3 likely reasons for this unusual behavior.
-Fay was in a strengthening phase as it approached southwest Florida at land fall.
-The unusually low and swampy topography provided little friction for Fay, and the high content of warm Everglades water in the landscape provided a positive feedback loop for intensification.
-Fay's outer bands remained over warm ocean water on both sides and the feeder bands continued to feed moisture and energy into the center.

Weak steering currents have put Fay on an erratic track. This type of environment makes it extremely difficult to forecast Fay's path in the future.

After 2 land falls in Florida already in the Keys and southwest Florida, Fay is scheduled to make a 3rd land fall today in northeast Florida on the Atlantic coast. A few of the computer models have Fay crossing Florida into the Gulf before making a 4th Florida landfall in the panhandle!

The primary danger from tropical storms is flooding rain. Slow moving Fay has produced some 17 to 25 inch totals just north of Melbourne, Florida. Some 30" rain totals are quite possible with Fay.

Too bad Mother Nature doesn't spread things out more evenly. We could use a few of those inches in parts of Minnesota, and Florida residents would gladly offer that precious rain as our gift!

PH

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Comments (1)

Didn't Andrew (1992) also increase in strength after making landfall?

And is the actual landfall really that important? Sure, it's an interesting thing to watch, but is it any worse if the eyewall sits 5 miles offshore (or stays onshore)? A good deal of convection will remain over the water.

Tropical cyclones which have made landfall go through a diurnal cycle. During the evening and night, the core becomes quite active and the feeder bands weaken. During the day (and it starts around 10am local, I kid you not), the central convection weakens and the storms on the periphery (the spiral arms) begin to increase in intensity and areal coverage.

The eruption of convection during midmorning (about the time of day you'd start to see small popcorn cumulus under midlatitude high pressure) is probably due to the patchy nature of the cloud deck over the land, allowing differential heating (and just plain heating) to cause a conditionally unstable air mass to further destabilize. A land-falling tropical cyclone brings a very moist and warm air mass with it, so it probably just needs a little bit more low-level destabilization to get things going on the land.

Why the central convection goes through its cycle is a mystery to me. Perhaps it has something to do with the outer band convection waxing and waning, or maybe it has something to do with solar radiation causing a more baroclinic environment (versus the barotropic conditions these storms like).

Posted by Chris B. Critter | August 21, 2008 3:40 PM

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