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Alberto nears hurricane intensity

With the 11AM advisory, the National Hurricane Center bumped the intensity of Tropical Storm Alberto to 70 mph. This was a little bit stronger than I expected (see last post), but not too far off. The main reason Alberto has intensified over the last 6 hours has been intense convection to the northeast of the (old) storm center. A new center of circulation formed underneath the intense convection, leading to deepening.

Figure 1. Infrared satellite image of TS Alberto. (Source: NHC)

Figure 2. Water vapor image of the Gulf of Mexico. (Source: NRL)

Also enhancing the convection was the Loop Current in the Gulf of Mexico. Alberto is positioned nearly directly over a warm tongue of water. This warm water led to additional instability, allowing convection to fire more easily in the face of strong southwesterly shear.
Figure 3. Sea-surface temperatures for the Atlantic ocean. Notice the warm tounge of water positioned roughly where Alberto is located.(Source: UM-RSMAS)

This shear will be the limiting factor as to how intense Alberto can become. Alberto is still centered over a region experiencing southwesterly shear at 25 kts. As Alberto moves away from the warm water, the shear will have a larger effect on the storm, weakening it before it makes landfall.
Figure 4. Shear values in knots over the Gulf of Mexico and Carribean. The red line indicates a shear value of 20 kts, the green line 30 kts, and the aqua line 40 kts. Alberto is located in a region of shear of about 25 kts. (Source: UW-CIMSS)

The forecast models have been trending to the west over the last few model runs. I think this should be about right, with landfall somewhere south of Tallahassee, in the western part of the NHC cone. It looks like while this system's primary nuisance will be heavy rainfall, storm surge along the coast will also be important. The shape of the continental shelf along the Florida panhandle is such that it gets worse than usual surge from tropical cyclones. NHC is forecasting surge values as high as 8-to-10 feet. Stay tuned to The StormTrack for more.

Posted by Adam Moyer | Permalink