Weather Nerd

Hurricane Gustav a major threat to Gulf Coast

Get used to that phrase — “Hurricane Gustav.” You’ll be hearing a lot of it over the next week or so.

Gustav was upgraded to hurricane status at 2:20 AM EDT, and it has continued to strengthen since then. Winds are at 85 mph as of 5:00 AM EDT, and pressure is at 984 mb. [UPDATE: Make that 90 mph and 981 mb, as of 8am EDT. It could become a Category 2 hurricane later today.]

The NHC discussion paints a picture of an increasingly concerning situation:

GUSTAV HAS CONTINUED TO INTENSIFY DURING THE LATE NIGHT HOURS. AN AIR FORCE RESERVE RECONNAISSANCE MISSION HAS FOUND FLIGHT-LEVEL WINDS OF [104 MPH]…PEAK SFMR SURFACE WINDS OF [87 MPH]…AND A RECENT ESTIMATED PRESSURE OF 984 MB. THE INITIAL INTENSITY IS CONSERVATIVELY RAISED TO [85 MPH]. SATELLITE IMAGES SHOW AN ORGANIZING PATTERN WITH A CENTRAL DENSE OVERCAST BECOMING MORE PROMINENT AND GUSTAV IS LIKELY NOT DONE INTENSIFYING BEFORE IT PASSES OVER SOUTHWESTERN HAITI LATER TODAY. SOME WEAKENING IS SHOWN IN 24 HR DUE TO THE LAND INTERACTION WITH HAITI. THEREAFTER…THE HURRICANE IS FORECAST TO BE OVER EXTREMELY WARM WATERS WITH RELATIVELY LIGHT SHEAR. THE OFFICIAL INTENSITY FORECAST IS INCREASED AND NOW CALLS FOR GUSTAV TO BE A MAJOR HURRICANE [WITH 115 MPH WINDS] IN THE NORTHWESTERN CARIBBEAN SEA [BY SATURDAY]. IT IS WORTH NOTING THAT BOTH THE GFDL/HWRF FORECAST SHOW AN EVEN STRONGER HURRICANE.

Indeed, the GFDL shows Gustav as a monster Category 5 hurricane peaking at 180 mph winds on Saturday as it enters the Gulf of Mexico and ominously stalks the central Gulf Coast:

An important caveat: computer models are inherently imprecise, especially with regard to intensity. Indeed, as Eric Berger writes, “It’s important not to focus on these precise details of these intensity forecasts as they’re almost assuredly wrong.” (The unanswerable question, of course, is precisely how they’ll be wrong.) One aspect of the GFDL forecast that seems especially likely to be wrong is the timing: the GFDL has Gustav moving much faster than most of the models do. The official NHC forecast doesn’t show Gustav entering the Gulf until Sunday morning.

“What is clear,” Berger writes, “is that Gustav will be traversing warm waters and will have favorable conditions for strengthening. It’s therefore appears likely Gustav will become a major hurricane.” The NHC agrees: “MOST INDICATIONS ARE THAT GUSTAV WILL BE AN EXTREMELY DANGEROUS HURRICANE IN THE NORTHWESTERN CARIBBEAN SEA IN A FEW DAYS.” And, I would add, in the Gulf of Mexico a couple of days after that.

Side note: If Gustav is indeed a major hurricane — maybe even a Category 4 or 5 behemoth — in the western Caribbean, with its sights set on the Gulf of Mexico, by week’s end, it could steal a bit of thunder from Barack Obama’s big acceptance speech on Thursday, and from John McCain’s expected runningmate announcement on Friday. The impact on the Republican convention next week could be even more significant, as the convention might coincide with a U.S. landfall. This could be especially awkward if McCain’s V.P. pick happens to be Louisiana Governor Bobby Jindal or Florida Governor Charlie Crist, who might have to skip the convention altogether, depending on Gustav’s timing and track.

Anyway, back to the NHC discussion:

THE BIGGEST CHANGE TO NOTE THIS MORNING IS A DRAMATIC SOUTHWESTWARD SHIFT WITH ALMOST ALL GUIDANCE. A LARGE UPPER TROUGH OVER THE WESTERN ATLANTIC IS EXPECTED TO MOVE EAST AWAY FROM GUSTAV…LEAVING RIDGING OVER THE BAHAMAS AND FLORIDA. GLOBAL MODELS HAVE COME INTO MUCH BETTER AGREEMENT THAT THE HURRICANE WILL TURN TO THE WEST-NORTHWEST OR EVEN WEST IN A DAY OR SO DUE TO THIS BUILDING RIDGE. THE OFFICIAL FORECAST HAS BEEN ADJUSTED SOUTHWESTWARD BEYOND 24 HR BUT IS STILL ON THE NORTHERN EDGE OF THE GUIDANCE ENVELOPE. THE FORECAST COULD HAVE BEEN SHIFTED EVEN MORE TO THE LEFT BUT WE’D PREFER TO WAIT UNTIL THE GUIDANCE BECOMES MORE STABLE.

It’s way too early to know where, exactly, Gustav will go. But, for now at least, the computer models seem to be zeroing in on the central Gulf Coast region:

As always, such a forecast trend raises alarm bells vis a vis New Orleans, not necessarily because it’s the most likely target (again, it’s way too early to know that), but because the Big Easy remains by far the most vulnerable American city to a direct hit from a major hurricane — which, I remind you, Hurricane Katrina was not; Katrina made landfall well east of New Orleans as a weakening storm, and was by no means the “worst-case scenario.”

Bottom line, if I lived in New Orleans, and I didn’t own a car, I would start asking around among my friends who do own cars: Are you going to be around this holiday weekend? If there’s an evacuation, can I have a ride? Just in case.

Also, if I were Mayor Ray Nagin, I would be dusting off those evacuation plans (for bussing people out of town, etc.) that were inexplicably never used during Katrina. Time to re-familiarize yourself with the details — again, just in case.

P.S. Eric Berger points out an additional reason for concern:

People are buzzing about Gustav because it seems to have the best chance of any tropical system since the record 2005 Atlantic hurricane season’s Katrina, Rita and Wilma to traverse the central Gulf of Mexico, where the loop current stands ready to aid in the rapid intensification of a hurricane.

It’s also the time of year, from now until the end of September, when the Gulf waters are at their warmest. So if we’re to have a major hurricane strike the Gulf coast this year, now’s the time.

A glance at the Tropical Cyclone Heat Potential map shows that, if it follows the expected track, Gustav will be traversing some of the most explosively warm waters in the entire ocean:

gustav-warmwater.png

It’s easy to see why people are concerned. This could be a bad one, folks.