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Weather Nerd

Uncertainty Continues Regarding Isaac’s Track, Intensity

August 26th, 2012 - 12:16 am

[NOTE: check the blog homepage and follow me on Twitter for the latest all weekend.

For an overview of the situation with Tropical Storm Isaac as of tonight, including specifically the significant threat to New Orleans, please see my main Saturday-evening post, "Déjà Vu: Isaac’s Katrina Moment?"]

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The much-anticipated 00Z ECWMF (Euro) model has just come out, and it doesn’t push Tropical Storm Isaac as far west as the GFS, HWRF, and a number of other models. It does show a major westward shift compared to the previous Euro run, from a landfall in Florida’s Big Bend to a landfall near Mobile, Alabama:

ecm_mslp_uv850gulf_tropical_5 ecm_mslp_uv850gulf_tropical_4-mobile

But because the GFS and the Euro — the two best-performing computer models — continue to disagree, with the GFS taking Isaac catastrophically into New Orleans while the Euro takes it to Mobile, substantial uncertainty will remain about Isaac’s track. Dr. Ryan Maue predicts the Euro’s projected landfall in Mobile “will prevent NHC from taking track any further west than that” until after another Euro run, which in turn means “it won’t be until [the] 5 pm advisory tomorrow before NHC expresses certainty on Landfall point — after ECMWF 12z at 2:15 PM.” In the mean time, New Orleans will almost certainly come to be in the “cone” by Sunday morning, but likely won’t be on the official track “line” until later, even if the GFS continues to predict a landfall there.

(To be clear: a disastrous strike on New Orleans is only one among many scenarios that could occur. Mobile, Pensacola, Panama City — you are all still in play. Heck, if the GFS’s westward drift continues, it’s conceivable that points in central or western Louisiana could end up being in play too. My focus on New Orleans doesn’t imply that New Orleans is the likeliest landfall spot, but only that it’d be the most catastrophic by far, and thus warrants a great deal of attention.)

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