Tropical Storm Ernesto update 26 Aug 1730L

August 26, 2006

It’s been one of those days for the National Hurricane Center forecasters.

First off, the 12Z model output continues to be fairly unhelpful as there are a couple of key models offering solutions that are quite implausible.

Secondly, the Hurricane Hunter that flew into Ernesto the afternoon found that the center of the storm had reformed to the northeast of where it was assumed to be at. Worsening matters, the plane had communication problems and had to fly back to base. As such, the current motion of Ernesto is uncertain; it’s unclear whether there is a more northerly motion ocurring, or whether it was just a blip in an overall westward/west-northwestward motion. See the 5 PM discussion for the forecaster’s account of these trials and tribulations.
The recon plane was able to to ascertain that Ernesto has continued to strengthen; a dropsonde observation suggested surface winds of 50 knots, which when rounded up, equates 60 mph. The plane has since relaunched and is at the edge of the storm as I type this.

The upper-atmosphere element of the intensity forecast remains unchanged. Ernesto is expected to receive more favorable conditions as time goes by. Of course, the increasingly warm Sea Surface Temperatures along his path aren’t going anywhere either. The wildcard is the prospect of extended interaction with land. The 12Z GFDL forecast track features a somewhat implausible trek over the Cuba length-wise, that causes its peak intensity forecast to be 85 knots (100 mph). The 18Z SHIPS forecast that accounts for land interaction (and uses the NHC official track for its forecast) brings Ernesto up to 89 knots (100 mph) and the SHIPS forecasts that pretends there is no land anywhere brings it up to 96 knots  (110 mph). The intensity forecast of the NHC goes to the high-side of these forecasts, predicting an intensity of 105 knots (120 mph), probably because of the earlier GFDL forecasts that did not have Ernesto interacting with land as much.

The forecast track has shifted a little bit further east. Again, I urge people to focus on the cone at this time, not the center track. The recent uncertainty over the current motion of Ernesto has made a lousy situation worse as far as confidence in the track forecast goes. In my last post, I mentioned that one shouldn’t take stock in the models until after a Gulfstream IV flight has flown to collect upper air data to be fed to the models. The first such flight will take place on Sunday afternoon and will collect data for that evening’s 00Z model runs, which in turn guide the NHC’s forecast for 5 AM Monday morning.

As such it remains a “watch and think about what you would do if the storm comes your way” for residents along the Gulf Coast. The area of concern is expanded to include the west coast of Florida. While the model runs suggesting a west coast strike seem unlikely, the uncertainty of the current motion of Ernesto causes a bit of concern that they may be on to something, so they need to join the people  from Texas to the Big Bend of Florida in keeping an eye on Ernesto’s progress.


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