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Gustav explodes to Cat. 4 with 145 mph winds

August 30th, 2008 - 10:23 am

EXPECTED TO BECOME CATEGORY 5 OVER GULF OF MEXICO

Nagin urges everyone to leave New Orleans now; mandatory evacuation to begin tonight

[NOTE: WWL-TV in New Orleans is now streaming live. Their live-stream had great Katrina coverage.]

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Hot off the presses, at 1:20 PM EDT:

DATA FROM AN AIR FORCE RECONNAISSANCE AIRCRAFT INDICATE THAT GUSTAV HAS CONTINUED TO STRENGTHEN AND NOW HAS MAXIMUM WINDS NEAR 145 MPH…230 KM/HR WITH HIGHER GUSTS.  THIS MAKES GUSTAV AN EXTREMELY DANGEROUS CATEGORY FOUR HURRICANE ON THE SAFFIR-SIMPSON HURRICANE SCALE.  A SPECIAL ADVISORY WILL BE ISSUED AT ABOUT 200 PM EDT TO MODIFY THE INITIAL AND FORECAST INTENSITIES.

Yikes.

[UPDATE: The 2pm EDT special advisory is now out. The discussion states:

YESTERDAY AT THIS TIME WE CONVEYED THAT RAPID INTENSIFICATION OVER THE NORTHWESTERN CARIBBEAN WAS POSSIBLE...BUT THIS IS A LITTLE MORE THAN WHAT WE HAD IN MIND IN SUCH A SHORT TIME.  THE HURRICANE HAS REACHED CATEGORY FOUR STATUS WITH AN INTENSITY OF [145 MPH]…HAVING BEEN A STRONG TROPICAL STORM JUST ABOUT 24 HOURS AGO.  . . .  THE AIRCRAFT FIXES
INDICATE THAT A NORTHWESTWARD MOTION HAS RESUMED…AND THE INITIAL
MOTION ESTIMATE IS 315/12…RIGHT ALONG THE PREVIOUS ADVISORY TRACK.  NO CHANGES TO THE 1500 UTC FORECAST TRACK HAVE BEEN MADE…BUT THE INTENSITY FORECAST HAS BEEN ADJUSTED UPWARD THROUGH 96 HOURS.  GUSTAV COULD INTENSIFY SOME MORE DURING THE NEXT FEW HOURS OVER WATER…AND ONE CANNOT RULE OUT CATEGORY FIVE INTENSITY BEFORE CROSSING CUBA.  THE FORECAST NOW CALLS FOR A PEAK AT [160 MPH]…CATEGORY FIVE INTENSITY…OVER THE SOUTHERN GULF WHERE OCEAN HEAT CONTENT WILL STILL BE HIGH…FOLLOWED BY A VERY GRADUAL WEAKENING OVER THE NORTHERN GULF WHERE OCEAN HEAT CONTENT IS LESS.]

The barometric pressure is now at 945 mb, a 43-mb drop in just over 24 hours, and a 29-mb drop in just over 12 hours — a classic example of rapid deepening.

Hopefully, Gustav is done intensifying for the moment. Even if it is, it’s about to absolutely slam Cuba, delivering a much heavier blow than they were probably expecting.

Here are the visible and infrared satellite views, as of 12:45 PM EDT:

gustav-cuba.jpg

gustav-cuba.jpg

Already a remarkable and terrifying storm. And remember, after Cuba (which will probably weaken Gustav a little bit, though not much, and at great cost to the poor souls who live there), the Loop Current lies ahead.

The only silver lining is the likelihood of weakening once Gustav gets past the loop current and moves into the northern Gulf of Mexico, where the water is cooler and shear may be higher. Unfortunately, as we learned during Katrina, a lengthy stint as a Cat. 4 or 5 (north of Cuba) will allow Gustav to build up a storm surge that won’t immediately die down once it weakens.

Moreover, if Gustav ramps up to Category 5 strength over the Loop Current (which now seems more likely, as the explosive intensification over the last ~12 hours will give it a stronger “starting point”), the pre-landfall weakening will need to be pretty substantial to prevent a real catastrophe somewhere.

But where?

The official forecast, as of 11am EDT, continues to show a landfall in central Louisiana, and all of the best computer models are bringing Gustav ashore far enough west of New Orleans that it would not be the “worst-case scenario” for the city — nor even Katrina Redux — though there might still be substantial flooding, property damage, and loss of life, depending on how geographically large the storm gets, and how well the levees hold up.

However, as Eric Berger explains and illustrates, a relatively small jog to the east could cause a storm surge in New Orleans that’s substantially worse than what Katrina did. Gustav need not make a literal “direct hit” for this to occur; if the eye passes immediately west of New Orleans, that would actually be the worst-case scenario.

Again, that’s not the forecast right now. But the storm’s recent northward jog is a bit nerve-wracking in this regard. Hopefully this trend does not continue. Land masses, like Cuba, sometimes do funny things to storms, and small “wobbles” now could have big impact on the precise landfall location 3 days from now. New Orleanians will be holding their breath at least until Gustav clears Cuba.

Well, actually, maybe they won’t be “holding their breath,” because they’re too busy evacuating. The staged evacuation in southeastern Louisiana is well underway, and although Orleans Parish — which goes last in the staged evacuation schedule — likely won’t see a mandatory evacuation order until tomorrow, some folks are already leaving, which is what I’d be doing if I were in their place.

[UPDATE, 2:21 PM: According to WWL-TV, New Orleans Mayor Ray Nagin "strongly encourages everyone to evacuate now," and the mandatory evacuation order will probably come at 7:00 PM tonight -- earlier than previously reported.]

In addition (and this is the crucial difference from the botched Katrina evacuation), folks without transportation are already being loaded on buses to escape the storm. Some may end up on good ol’ yellow school buses, due to the problems that Louisiana’s emergency contractor is having getting enough charter buses to the state. (You might recall that, in 2005, a bunch of school buses drowned, having never been used to attempt evacuation.)

The New Orleans Hurricane Center has much more on Louisiana’s preparations for the storm. See also the replay of Times-Picayune hurricane expert Mark Schleiftstein’s just-completed New Orleans live chat.

Finally, here’s a radar image of Gustav, from long-range Key West radar.

My daughter is about to wake up from her midday nap, and as I’m a daddy first and a weatherblogger second, I’m not sure how much more blogging I’ll be able to do this afternoon. I’ll try to post an update or two if conditions warrant. I’ll certainly blog some more this evening, once she’s in bed.

In the mean time, go to the National Hurricane Center for the latest official information on the storm, WWL-TV and the Times-Picayune‘s New Orleans Hurricane Center for the latest news on preparations, and the other websites in my blogroll for additional information.

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