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Weather Nerd

Irene weakens slightly, may not significantly re-strengthen

August 26th, 2011 - 6:05 am

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The answer to the question I posed before going to bed last night is… no. Irene’s winds didn’t “catch up” with the her barometric pressure overnight, turning the storm into a picture-perfect monster. Instead, she actually weakened slightly, from 115 to 110 mph — and she’s running out of time to re-strengthen. It looks like my post yesterday afternoon about a weaker Irene, which I almost immediately walked back, may have been right after all. (But DO NOT GROW COMPLACENT, folks in Irene’s path. Continue to prepare for the worst. The potential impacts of this storm — even if she never gets stronger than 110 mph again — are still, as a certain resident of Delaware would say, a big f***ing deal.)

From the 5am NHC discussion:

REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INDICATE THAT THE INTENSITY OF IRENE IS NOT QUITE AT MAJOR HURRICANE STATUS. …

WATER VAPOR IMAGERY AND ANALSYES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN SUGGEST THAT IRENE IS ENCOUNTERING LIGHT TO MODERATE SOUTHWESTERLY VERTICAL WIND SHEAR. THIS… ALONG WITH THE CURRENT CYCLONE STRUCTURE AND DRY AIR ADVECTING TOWARD THE HURRICANE IN WATER VAPOR IMAGERY… ARGUE AGAINST SIGNIFICANT STRENGTHENING… AND INDEED THE INTENSITY GUIDANCE SHOWS LITTLE CHANGE IN STRENGTH BEFORE LANDFALL. ON THE OTHER HAND…THE EYEWALL CONVECTION IS CURRENTLY STRONG…AND THE SEA SURFACE TEMPERATURES ALONG THE FORECAST TRACK ARE 28-29C. THIS SUGGESTS SOME MODEST STRENGTHENING IS POSSIBLE. IRENE IS EXPECTED TO BE NEAR THE CATEGORY 2/3 BOUNDARY WHEN IT REACHES THE VICINITY OF THE OUTER BANKS…AND SLOWLY WEAKEN AFTER THAT. AFTER MOVING INTO NEW ENGLAND…IRENE SHOULD WEAKEN QUICKLY AS IT UNDERGOES EXTRATROPICAL TRANSITION.

Irene is now expected, once again, to peak at 120 mph, and maintain that intensity for just 12 hours or so. That could change, in either direction, but the bottom line is that the odds of this hurricane becoming a high-end Cat 3. or even Cat. 4 — which would in turn increase the odds of Cat. 2 impacts in the northeast, and worsen the storm surge wherever Irene hits — are decreasing.

One major caveat: Irene still has to cross the Gulf stream. The NHC and the computer models know this, of course, and it’s probably part of the reason why they’re expecting re-intensification from 110 to 120 mph. Still, those deeply warm waters can affect hurricane intensity like jet fuel on a fire, and it wouldn’t be shocking if Irene experiences an unexpectedly pronounced spike in strength as she traverses them.

In any event, regardless of her exact intensity, folks in Irene’s path should continue to take it very seriously. This is a still a huge, very serious hurricane. There will be major wind, storm surge, and rain impacts all across the Carolinas, mid-Atlantic and northeast this weekend. PREPARE! And if you’re advised or told to evacuate, EVACUATE! Far better safe than sorry when forecasts are so uncertain and the potential for disaster is so high.

Editor’s Note: Don’t miss “Personal Responsibility: Irene Prep.”

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