Let me begin with the standard caveats about uncertainty. 5-day track forecasts from the National Hurricane Center, while steadily improving year by year, still have an average error of around 250 miles. (That means, of course, that sometimes they’re even more wrong than that.) 5-day intensity forecasts are even shakier. That said, take a look at where the NHC believes a Category 1 hurricane named Isaac will be next Monday, which happens to be the first day of the Republican National Convention in Tampa, Florida:
Isaac is presently a Tropical Storm with winds of 45 miles per hour, and its inner core actually seems to have weakened overnight. But “the overall structure of the storm is improving,” according to the NHC’s 11am EDT discussion, which suggests its long-term prospects may be improving.
But with Tampa on everyone’s mind, the focus is on the track. The NHC sounds pretty confident about the first 48-72 hours of the forecast, bringing the storm into or near Hispaniola. After that, despite the relative consistency of the NHC forecast tracks since Isaac formed yesterday morning, there is more uncertainty — indeed, an increasing amount of uncertainty this morning, according to the NHC:
AFTER [48-72 HOURS]…THE [RIDGE OF UPPER-LEVEL HIGH PRESSURE SITTING ACROSS FLORIDA AND THE SOUTHEASTERN U.S. TO ISAAC'S NORTH] IS EXPECTED TO WEAKEN SOMEWHAT AS A MID/UPPER-LEVEL TROUGH MOVES ONTO THE EASTERN UNITED STATES. THE MODELS DIVERGE ON THEIR FORECASTS OF THE RIDGE. THE ECMWF [EUROPEAN COMPUTER MODEL] DOES NOT BREAK THE RIDGE…AND THUS FORECASTS A MORE WESTWARD MOTION NEAR OR SOUTH OF CUBA. THE CANADIAN AND NOGAPS HAVE A LARGE BREAK IN THE RIDGE AND TURN ISAAC NORTHWARD EAST OF FLORIDA. THE UKMET HAS A BREAK IN THE RIDGE OVER THE NORTHERN GULF COAST AND MOVES THE CYCLONE OVER THE FLORIDA PENINSULA. THE GFS SHOWS A BREAK IN THE RIDGE EAST OF FLORIDA…BUT FORECASTS ISAAC TO BYPASS THE BREAK AND MOVE NEAR THE SOUTHWEST COAST OF FLORIDA. THIS DECREASED-CONFIDENCE PORTION OF THE FORECAST TRACK IS SHIFTED A LITTLE WEST OF THE PREVIOUS TRACK TO LIE NEAR THE CONSENSUS MODELS.
A “little to the west of the previous track” means directly aimed at Tampa, at least for the moment. But more important is that “decreased confidence” language. Forecasters really aren’t sure what’s going to happen after Isaac hits, or brushes, Hispaniola on Friday. This thing could wind up staying south of Cuba, and perhaps eventually slamming the Yucatan Peninsula of Mexico. Or it could come up the Eastern Seaboard… or head out to sea. A lot of possibilities remain on the table. “From Mexico to Maine,” as I keep saying.