Tropical Depression Two forms in the Gulf of Mexico

July 7, 2010

Waiting virtually until the last minute before the nominal advisory time of 10 PM CDT, the National Hurricane Center has classified former Invest 96 as Tropical Depression Two.

At 7 PM CDT, Stacy Stewart and John Cangialosi issue the evening Tropical Weather Outlook increasing the probability of tropical cyclone formation to 80%, citing observations from NOAA research aircraft.    Contemporaneous satellite intensity estimates rate the system as a tropical depression. Infrared image from 45 minutes before that:

As before, the heavy thunderstorm activity is not in the center of the storm circulation; the heaviest that can be seen here is well removed from it. That trend continued later into this evening:

Because of that, it was surprising to see the upgrade happen, despite observations from the NOAA aircraft reinforcing the evidence of a surface circulation (given this trend, I would be surprised to see 06Z satellite estimates stay where they were at 00Z). The discussion explains this in a sentence: ”

ALTHOUGH INNER-CORE CONVECTION HAS WANED OVER THE PAST FEW HOURS...OUTER CONVECTIVE BANDING TO THE EAST OF THE CENTER HAS BEEN INCREASING."

True enough, I suppose.

The dilemma that Stewart and Cangialosi faced was that intensity guidance showed that if there’s a tropical depression, there would be a tropical storm, therefore, there should be tropical storm warnings.  It is awfully awkward to post warnings without a classified system. That may have been a bit of the motivation in this case.

Landfall of a weak tropical storm in vicinity of the Rio Grande is forecast to occur by 7 PM Thursday night. As I mentioned in the conclusion of my previous post, rainfall on already saturated ground is more of a concern than any winds this may bring.

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