Tropical Storm Ernesto update 26 Aug 0530L

August 26, 2006

Tropical Storm Ernesto intensified overnight.  Pressure has dropped down to 997 millibars.  While the 5 AM advisory reported Ernesto having winds of 45 mph, the final pass of the reconnaisance plane through northeast quadrant (which happened about half an hour after the advisory was released) suggests that surface winds are now 50 mph, and still on the increase owing to the ongoing drop in pressure.

There’s not much change in the short term outlook, as the forecast continues to bring Ernesto over Jamaica as a tropical storm. Recent events may prove to cause the forecast to be slightly under; Ernesto could make hurricane strength before Jamaica, provided that he does not advance into the 20+ knots of shear that lay to his west. After that, the global models are unaminous in setting up a favorable upper air enviroment for Ernesto. That combined with the higher levels of Tropical Cyclone Heat Potential would serve to quicken the pace of intensification.

The peak of the intensification forecast by the intensity models have increased, with the SHIPS model raising the storm to 100 mph and the GFDL being more agressive, raising Ernesto to Category 4 strength at 140 mph. The official forecast is an average of the two.

There has been no clarity addded to the latter part of the forecast.  There is a bit of a consensus among the dynamic models in bringing the storm about as far west as Alabama before turning it to the east with a landfall in the Florida panhandle being the end result. Individual members of this consensus have shown variability, however, over the past couple of forecasts, which takes a little bit of confidence out of that solution. Also, it’s not a straight-forward dyanmics situation that brings forth the result, and as such the forecast outcome is highly prone to change.

The NHC forecast for the late term continues to not favor a particular scenario; it’s pretty much just a straight line drawn down the middle of the range of the forecasts generated by the models. One should pay much more attention to the cone of the concern than the center line at this point. Three recent examples of why this is the case:

The first two examples are from 2004 and somewhat inverses of eachother; also, both were in a similar position to the one Ernesto is in now.

– At one point the center-line of the forecast for Charley suggested a Pensacola strike. The next run of forecast models featured a significant intensification of a feature that would cause it to instead go to southwest Florid, (which was at the extreme eastern end of the cone.

– The forecast for Ivan, for a fair amount of time was for it to hit the west coast of Florida, high pressure ridging proved to be stronger than the models were forecasting at the time, and Ivan went on to hit Pensacola instead.

Last example is from one year ago today

– Just 72 hours before landfall, and right before a marked westward shift in the forecast models, the centerline Katrina forecast was through the Florida Panhandle. Mississippi and eastern Louisiana were in the cone.  Before their shift, the models were in near unaminous agreement on a panhandle hit.

I wouldn’t put too much weight on the forecast models until they are fed the upper air data collected by the GulfStream IV and that won’t happen until Sunday evening at the earliest. It would not be surprising to see the NHC continue their neutral hedge until then.  People from the Big Bend of Florida to Texas should keep an eye on it this weekend and be thinking about the preparations that they would start making next week if Ernesto were to head their way.


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