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Weather Nerd

Gustav weakens!

August 31st, 2008 - 4:08 am

Good news from the 5:00 AM EDT discussion: Gustav’s “starting point” for today’s expected intensification will be lower than previously thought.

APPARENTLY…THE INTERACTION WITH WESTERN CUBA TOOK MORE OF A TOLL ON THE HURRICANE THAN EARLIER ESTIMATED. DATA FROM THE AIR FORCE HURRICANE HUNTER SHOW THAT GUSTAV HAS WEAKENED WITH MAXIMUM FLIGHT-LEVEL WINDS OF [129 MPH]…SFMR WINDS OF [113 MPH]…AND A MINIMUM CENTRAL PRESSURE OF 958 MB. SATELLITE IMAGES CONFIRM THIS WEAKENING TREND AS THE EYE NO LONGER VISIBLE. AIRCRAFT AND RADAR OBSERVATIONS ALSO INDICATE THAT THE EYE HAS EXPANDED TO AROUND 25 N MI IN DIAMETER. THE INITIAL INTENSITY IS LOWERED TO [125 MPH]…AND GUSTAV MAY EVEN BE A LITTLE WEAKER FOR THE MOMENT. HOWEVER THIS WEAKENING IS FORECAST TO BE SHORT-LIVED AS THE HURRICANE TRAVERSES THE RELATIVELY HIGH HEAT CONTENT OF THE GULF LOOP CURRENT. BEYOND 24 HOURS…THE HEAT CONTENT DECREASES AND MOST MODELS INCREASE THE VERTICAL WIND SHEAR NEAR GUSTAV DUE TO AN UPPER-LEVEL LOW OVER THE WESTERN GULF. IN ADDITION…NONE OF THE NUMERICAL GUIDANCE SHOW SIGNIFICANT RESTRENGTHENING OF GUSTAV…ALTHOUGH ADMITTEDLY THE SKILL OF THESE MODELS IS RATHER LOW. THE OFFICIAL INTENSITY FORECAST IS REDUCED FROM THE EARLIER ONE…BUT STILL SHOWS GUSTAV AS A MAJOR HURRICANE AT LANDFALL.

[UPDATE: Gustav's top winds are now down to 120 mph, as of 8am EDT. This decrease probably does not represent not further weakening, but rather confirmation from the latest recon mission that Gustav was, and remains, "a little weaker" than the previous advisory estimated.]

Hopefully the weakening is such that Gustav, in its less-organized state, will be unable to fully take advantage of the Loop Current. We’ll see. Certainly, my “175 mph” scenario seems far less likely now.

I’ll have another update later in the morning, probably after the 11:00 AM advisory comes out.

UPDATE, 8:06 AM: Alan Sullivan pours cold water on my hopes that the Loop Current won’t do its worst:

Winds are estimated at 120 mph. Central pressure has risen a bit more to 960 mb. That’s the good news. But Gustav’s eye is beginning to reappear in the satellite imagery, and intense convection is wrapping more completely around the center. I expect we will be seeing a fully developed core again within a few hours. I still anticipate a significant pressure drop and increase in winds later today. Weakening will resume before tomorrow’s landfall, but it may be too late, because the storm is moving so fast.

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