August 27, 2006
A unaminous eastward shift in the 00Z runs of the global forecast models plus the GFDL has caused a very unusually dramatic shift in the National Hurricane Center forecast. The five day cone of uncertainty now covers Florida exclusively, with the centerline being across Tampa.
The shear that was impeding Ernesto’s intensification has abated and the result has been steady strengthening for Chris this evening, culminating in a dropsonde observation from the reconnaisance plane indicating that Ernesto is now the first hurricane of the 2006 season.
The overall motion of the storm has been to the west-northwest, but with an occasional bump to the north owing to relocations of the center. The result has been that Chris should pass to the north of Jamaica cleanly. The forecas track then takes Ernesto along the southern coast of Cuba and then crossing Cuba along a path that puts the hurricane just west of the Keys on Tuesday night.
The intensity forecast maintains the storm as hurricane for the trek across Cuba, and the intensifies it to a category three before landfall.
A huge wildcard in the intensity forecast is exactly where Ernesto goes into Cuba at. The official forecast takes it very near the highest point on the island, the 6750 foot high Pico Turquino. Hurricane Ella of 1958 went more or less square into it as a category three hurricane and came out as a tropical storm. Cleo of 1964 passed just to the south and went from a category three to a one in the process. If the future track of Ernesto were to go just as forecast, or ever so slightly to the right over the next 36 hours, then the weakening would probably be quite a bit more substantial than the forecast currently shows.
Other than that, however, there isn’t much impediment for Ernesto. The upper air enviroment is forecast to be extremely favorable for strengthening. The experience of Charley 2004 shows what can happen to a hurricane in a favorable enviroment, in spite of the seemingly limited space between Cuba and Florida. A track ever slightly left of the current forecast, keeping the storm mostly over water with the exception of a brief jaunt over the flat terrain in the center of Cuba would set up quite a worrisome situation.
The scenario bringing Ernesto into peninsular Florida is the erosion of a mid-level ridge of high pressure that would otherwise push Ernesto to the west. It is the sort of scenario that the models are often too eager to forecast (such as was the case during Ivan in 2004). Because of that there is a chance for the forecast to get pushed back to the west somewhat, especially if the upper-air mission to be flown tonight found a stronger ridge than the models are depicting. However, the GFS model, whose output yesterday afternoon was eyed with skepticism by yours truly and dubbed as “dubious” by the NHC forecaster has shifted its track even further east, bringing the storm ashore in the middle of the Keys and then up the middle of peninsular Florida. The NHC forecast puts that forecast and a NOGAPS forecast depicting a strafing of southwest Florida to its right. (A third global model, the UKMET, has a forecast similar to that of the hurricane center’s. The fourth member of the respected GUNS consensus, the GFDL is currently a left outlier, as it brings Ernesto further west turning it at a point that would threaten Pensacola).
Owing to proximity, residents Florida from Tampa south need to keep a close eye on Ernesto now. Residents of the southernmost Atlantic coast should be aware that they are inside the three day cone. Further north and west a somewhat more casual watch can be kept, again because of distance from the storm, but it would be unwise for residents of Pensacola and points east to drop Ernesto entirely from their radar screen. As I outlined above, while the models are unaminous in threating Florida, they aren’t exactly unaminous in forecasting who will get the worst from Hurricane Ernesto.