Weather Nerd

Flabbergasted by Fay

I guess Tropical Storm Fay’s strengthening over land is even more remarkable than I thought. Meteorologist and weatherblogger Dr. Jeff Masters, co-founder of Weather Underground (the commercial weather service, not the terrorist group), is utterly astounded:

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 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.

Here’s a visible satellite view, as of 3:45 PM EDT:

fay-satellite-florida.JPG

So… what next? Alan Sullivan summarizes the computer-model split:

As ever, there is very sharp divergence in the models of Fay’s future course and strength. One version has a weakening system that turns NNW and never gets back over water; it just moves into Georgia. Another gains the Atlantic, but makes such a sharp left turn that it winds up traversing the NE Gulf and far, far to the west. Yet another coasts seaward, then turns NNW toward Savannah. And one outrider goes all the way opposite — NE and away, with no lefthand curve at all.

See for yourself here and here. (Ignore CLP5 and XTRP, which are not real models.)

“What to believe?” Sullivan asks. “At the moment my pick is Savannah, with Fay as a strong tropical storm, but probably not a hurricane.”

For his part, Dr. Masters — who had previously expressed skepticism about the possibility of significant restrengthening prior to a Florida/Georgia border area landfall — now says:

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.

It’ll be very interesting to hear what the National Hurricane Center has to say about Fay at 5:00 PM EDT.

P.S. The Palm Beach Post‘s Kevin Deutsch and AccuWeather’s Jesse Ferrell have more on Fay. Meanwhile, the Miami Herald has full coverage of the storm’s impact.

UPDATE: The 5pm EDT advisory is out. Half a day after landfall, Fay’s maximum sustained winds are now “conservatively” set at 65 mph — that’s 5 mph more than when it came ashore. The discussion states dryly, without hazarding an explanation, that “FAY DID NOT WEAKEN OVER LAND AS ANTICIPATED AND IN FACT…IT IS STRONGER THAN IT HAS EVER BEEN SO FAR.”

The NHC has given up on predicting weakening during Fay’s remaining 12 hours over land. The public advisory states simply, “MAXIMUM SUSTAINED WINDS ARE NEAR 65 MPH…100 KM/HR…WITH HIGHER GUSTS. SOME STRENGTHENING IS FORECAST DURING THE NEXT 24 HOURS.” The latter sentence is a remarkable statement, given that Fay is expected to spend fully half of those 24 hours over land. But at this point, who can argue? Throw out the rules, including the basic iron law that hurricanes only strengthen over water. It’s Fay’s world; we’re just living it.

The NHC discussion also states:

[FAY’S STRENGTHENING OVER FLORIDA] HAS PROMPTED A SIGNIFICANT CHANGE IN THE INTENSITY FORECAST. GIVEN THAT FAY HAS KEPT SUCH A WELL-DEFINED SIGNATURE ON RADAR AND ON SATELLITE…THE CHANCES THAT THE CYCLONE BECOMES A HURRICANE AS IT MOVES OVER THE GULF STREAM EAST OF FLORIDA HAVE INCREASED. THE INTENSIFICATION IS SUPPORTED BY SHIPS…THE GFDL AND THE HWRF MODELS…AND IS REFLECTED IN THE OFFICIAL FORECAST. …

THIS NEW DEVELOPMENT HAS PROMPTED THE ISSUANCE OF A HURRICANE WATCH FOR A PORTION OF THE NORTH FLORIDA AND GEORGIA COAST.

Here’s the latest forecast track and watches & warnings map. As always, focus on the “cone.”

UPDATE, 9:42 PM EDT: In the last couple of hours, Fay has finally started to decay a bit, and now looks somewhat less organized on radar. It remains to be seen how she’ll fare once she re-emerges over water in the morning.