NHC Track to MS or AL Coast

A center has just formed for the future Isaias as shown by the arcing cloud where I place an arrow. My take is that this will strengthen enough to be named by morning. There’s presently little motion, but the system should should be steered eastward by the westerlies as more thunderstorms extend to a higher level.

Here’s the official NHC forecast which I concur with. It calls for a fast moving, rapidly developing storm that reaches hurricane strength by the time it reaches the middle of the Gulf, but encounters shear and dies down a bit before making landfall as early as Friday evening in the Dauphin Island, Alabama area as a strong tropical storm. Note that the Slidell area is right at the edge of the cone and Gulfport-Biloxi is certainly within the margin of error for landfall as is Gulf Shores and Pensacola.

The formation of a center today has helped consolidate the forecasts. The majority of models, including the often maligned American GFS, are in or near the Mobile Bay area. The only big exception is the ECMWF from this morning which has a landfall near New Orleans and Slidell. BUT that was from this morning and didn’t include the center location or data from NOAA jets. These jets, criss- crossing the Gulf gathering upper air data plus the extra radiosondes (weather balloon observations) that have been made in the Southern Plains should give us an even better set of data to run tonight’s models. So, NHC has largely discounted that ECMWF run - something you don’t see very often.

The physical reason why the storm is forecast to move northeast is seen in this graphic showing the upper air winds. This was made earlier in the day before the NHC cone was created, but the idea is still valid.

Though it’s too early to nail this down, a few points can be made, all of them good:

1) The further west this storm heads, the weaker it should be because it will be bucking wind shear sooner.

2) The rainfall rates north and northwest of the storm will not be that great at landfall. I’m looking for a steady rain of possibly several inches rather than flash flooding deluges. The challenged is the timing of the storm- rain could start as early as Friday morning or as late as Friday evening and be over by daybreak Saturday or as late as Saturday afternoon. The MS Gulf Coast will get more rain that St. Tammany or New Orleans.

3) The tornado threat will be east of the center and probably won’t be an issue for Louisiana.

4) This will not be a big storm. Winds will die off rapidly 40 miles west of the center.

I’m not showing the time series forecast because it is based largely on the probably erroneous ECMWF. The bad news has nothing to do with the storm: I see no break into cool fall weather in sight. Highs on sunny afternoons will still it the mid 80s, but many mornings will be nice.