First things first. Today will be an important day in Isaac’s forecast history, as the computer models hopefully coalesce around a consensus track. This weekend will be even more important. I’ll update this blog as often as I can, but for the very latest updates, follow me on Twitter — @brendanloy.
Isaac’s wind speed is up to 60 mph as of 11:00 AM EDT, and its inner core is finally getting a bit better organized — though the window for further organization will end soon, as it reaches Haiti, and won’t really begin again until it pops off Cuba on Sunday. From the NHC’s discussion:
RECONNAISSANCE AIRCRAFT DATA AND SATELLITE IMAGERY INDICATE THAT ISAAC HAS BECOME BETTER ORGANIZED DURING THE PAST SEVERAL HOURS. WHILE THE CIRCULATION CENTER REMAINS ELONGATED EAST-TO-WEST WITH MULTIPLE EMBEDDED VORTICITY MAXIMA…THE LARGE CENTRAL AREA OF LIGHT WINDS HAS SHRUNK AS THE STRONGEST WINDS MOVE CLOSER TO THE CENTER. …
WHILE THE ORGANIZATION HAS IMPROVED…THE STRUCTURE OF ISAAC STILL DOES NOT FAVOR RAPID INTENSIFICATION DESPITE A VERY FAVORABLE UPPER-LEVEL WIND PATTERN. THE EARLY PART OF THE INTENSITY FORECAST SHOWS A LITTLE MORE STRENGTHENING THAN EARLIER…AND IT IS POSSIBLE THAT ISAAC COULD BE NEAR HURRICANE STRENGTH WHEN IT REACHES HISPANIOLA. LAND INTERACTION WILL LIMIT THE INTENSITY FROM 24-48 HR…AND THIS PART OF THE FORECAST MAY NEED SOME ADJUSTMENT AFTER IT IS SEEN WHAT STRUCTURE ISAAC HAS AFTER CROSSING HISPANIOLA. ISAAC SHOULD STRENGTHEN OVER THE GULF OF MEXICO…WITH THE FORECAST SHOWING THE CYCLONE BECOMING A HURRICANE BEFORE REACHING THE NORTHERN GULF COAST.
At present, the forecast is for “just” a Category 1 hurricane to hit the northeast Gulf Coast on Tuesday night or Wednesday morning. The NHC believes the roughly 24-30 hours Isaac will have over the Gulf before landfall won’t be enough time to become a major hurricane. They’re probably right, but it’s important to remember that hurricane intensity forecasting is an inexact science, especially in the 4-5 day range. Dr. Jeff Masters thinks a major hurricane Isaac is still not out of the question: “It is possible that Isaac could be approaching Category 3 strength by the time it makes landfall on Tuesday on the Gulf Coast, as suggested by the latest 06Z run of the HWRF model.”
Meanwhile, as I mentioned in a brief post earlier, the computer models’ westward shift yesterday — which had caused some folks, myself included, to fear that the “trend” might result in a New Orleans landfall consensus by today — has instead reversed itself, edging slightly back east. More importantly, the confidence of the forecast has increased somewhat, as the computer models are coming into better agreement. New Orleans is still technically within the NHC’s cone of uncertainty, but no trusted computer model is calling for a landfall west of Mobile, AL:
This is good news for New Orleans, which is still America’s most vulnerable city to flooding from a major hurricane, and also good news in general because it means Isaac will have less time over water to restrengthen after exiting Cuba. It’s not such good news, of course, for anyone between Mobile and Tallahassee, which now appears to be the most likely landfall zone. (The Panama City area is where the current official forecast track takes Isaac, though as the NHC reminds us: “IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK DUE TO THE UNCERTAINTIES IN THE FORECAST AND THE FACT THAT ISAAC HAS A LARGE AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED WITH IT.”)