Weather Nerd

Fay, over land, gets better organized

Weatherblogger Alan Sullivan, who has been anything but bullish in his assessment of Tropical Storm Fay, looked at the radar around 8:00 AM EDT and concluded that Tropical Storm Fay — three hours after landfall — was “very near hurricane strength.” He noted “a distinct eye” and, in comments, pointed out that the minimum central pressure had dropped to 988 MB, which is generally around the borderline between a strong tropical storm and a minimal hurricane.

Another three hours later, six hours after landfall, Fay looks even better. The radar loop shows a tightening, organizing system, with a relatively symmetrical central core wrapping all the way around the center — for the first time in the storm’s life. And all this happened over land!

fay-overland-eye.png
NWS radar at 10:52 AM EDT.

While unusual, it isn’t totally unprecedented for a tropical cyclone to maintain its intensity for quite a while, and even strengthen slightly, over land — provided the land is low-lying and swampish, like in South Florida. (Hurricane Katrina did something similar during its trek over the Everglades, setting the stage for its subsequent rapid intensification en route to Louisiana and Mississippi.) Certainly, such terrain does not lend itself to rapid weakening.

What seems to have occurred is, Fay came ashore on the verge of an intensification cycle, and if Florida hadn’t gotten in the way, it would probably be getting appreciably stronger by now. (As Sullivan says, “This has been an unlucky system — which is fortunate for a lot of people.”) Instead, Fay is sucking in just enough moisture from the Gulf through its outer circulation, and from the Everglades & environs underneath it, to basically remain static in terms of wind speed and pressure — and is actually tightening up its structure in the mean time. [UPDATE: Sullivan explains: “In Florida and the Gulf Coast, tropical storms often tighten up near or just after landfall, presumably from onset of modest surface friction. These gentle coasts have very different effects compared with mountainous islands.”]

Sullivan speculated at 8am that the National Hurricane Center might upgrade Fay to hurricane strength, given the current observations. That would have been remarkable: a tropical storm upgraded by 15 mph, becoming a hurricane for the first time in its life, six hours after landfall! But, in the hot-off-the-presses 11:00 AM EDT advisory, the NHC demurred. It says the surface winds don’t support such a designation, even if the pressure and radar imagery seem to.

Officially, Fay remains a strong-ish tropical storm with 60 mph winds, the same as six hours ago. The discussion does acknowledge Fay’s apparently overland strengthening, though: “DOPPLER RADAR DATA AND SATELLITE IMAGES REVEAL THAT FAY HAS KEPT A WELL DEFINED PATTERN…AND IN FACT…RADAR SHOWS A RING OF CONVECTION WHICH RESEMBLES AN EYE FEATURE.”

Ultimately, this attempt at overland intensification is doomed to fail, because hurricanes depend on warm ocean water for their fuel, in much the same way that robots depend on old people’s medicine (which, coincidentally, is also in abundance in South Florida). So, some eventual weakening is inevitable.

That said, although the winds will decrease and the pressure will increase before Fay re-emerges over the Atlantic (which is now unanimously expected by the computer models), she may exit the Florida peninsula with a tighter, more well-defined structure than she entered it with. If that happens, re-development over the warm Gulf Stream waters could be fairly quick, and perhaps significant. The NHC alludes to this possibility in its discussion:

FAY IS FORECAST TO WEAKEN AS IT MOVES OVER LAND FOR THE NEXT 12 TO 18 HOURS. THEREAFTER…IT SHOULD REGAIN SOME STRENGTH DURING THE 24 TO 48 HOUR PERIOD WHEN FAY IS FORECAST TO BE OVER WATER JUST OFF THE FLORIDA EAST COAST. IF FAY MAINTAINS ITS CURRENT STRUCTURE ON RADAR…THE RATE OF INTENSIFICATION COULD BE HIGHER THAN INDICATED. AT THIS TIME…THE FORECAST INTENSITY [WHICH PREDICTS FAY TO STRENGTHEN MERELY FROM 45 MPH TO 50 MPH DURING ITS STINT OVER THE ATLANTIC] FOLLOWS CONTINUITY AND THE SHIPS INTENSITY MODEL. THE GFDL IS VERY AGGRESSIVE AND MAKES FAY A STRONGER CYCLONE OVER THE WATER JUST EAST OF NORTH FLORIDA. DO NOT RULE OUT THIS POSSIBILITY YET.

Here’s a look at that GFDL forecast, which shows a 110-mph, borderline Category 2/3 hurricane due east of Jacksonville on Thursday afternoon. Such a system could potentially make landfall anywhere along the Georgia or northeast Florida coasts.

So, stay tuned! Although Fay’s impact on southwestern Florida was something of an anticlimax, this “Joker” may be just getting started.

P.S. Dr. Jeff Masters is skeptical of the GFDL forecast. He wrote at 9am EDT: “Given the rather high levels of wind shear (15-20 knots) predicted to be over Fay late this week, plus Fay’s recent inability to build an eyewall in the 24 hours it had over the Florida Straits, I am discounting the GFDL model’s solution of a hurricane hitting Georgia.” I can’t dispute the point about wind shear, but I think the “inability to build an eyewall” argument may now be obsolete, given Fay’s overland structural organization. But Dr. Masters is a meteorologist and I’m not, so take my opinions with a major grain of salt. :)

Masters also looks beyond the likely third U.S. landfall near the Florida/Georgia border, to a potential fourth landfall next week: “I give Fay a 60% chance surviving its traverse over Florida, then turning back to the west over the northern Gulf of Mexico by Saturday. This would allow the storm to regenerate, before potentially making landfall again along the northern Gulf Coast between New Orleans and the Florida Panhandle early next week.”

A hurricane threatening New Orleans, just in time for the Democratic National Convention in Denver? Say it ain’t so, Landrieu!

P.P.S. Caveat: lest anyone be alarmed, I’m not serious about the “hurricane threatening New Orleans” thing. I was just a having a little fun vis a vis the Dems’ convention timing. But there’s no reason to think such a scenario is likely. Fay might drift toward the central Gulf Coast next week as a weak storm or remnant low, but it’s very unlikely to be a hurricane.