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August 2012

Isaac to Impact Hispaniola and Cuba, on Course for Florida After

   Posted by Levi at 4:57pm on August 24, 2012

Tropical Storm Isaac continued to struggle yesterday as its circulation was still decoupled, with the surface center off to the north of the mid-level center. The biggest pressure falls remained in the vicinity of the mid-level center, however, and thus overnight the system has reformed with what looks like a much better vertically-stacked center farther to the south. Convection is now trying to wrap up the eastern side of the storm, though the northwest quadrant is void of deep thunderstorms. The last recon mission found a stronger storm with 60mph winds and a pressure of 1000mb. Outflow is healthy all around the system, and the only truly limiting factor left is dry air getting entrained from the western Caribbean. Isaac should strengthen on approach to Hispaniola today, and if he passes only over the western tip of Haiti, extra water time before hitting Cuba could allow him to make a run at hurricane status. If the mountains of Hispaniola draw him north into the island more quickly, however, he will have less time to strengthen. The mountains of Haiti and Cuba will weaken Isaac a bit during the crossing, but due to improving environmental conditions, only moderate weakening is expected. Once in the Florida Straights, strengthening should quickly resume. The current forecast track has Isaac interacting with the Florida Peninsula rather quickly after exiting Cuba, and thus keeps Isaac a tropical storm. If, however, Isaac passes just on either side of Florida, it will have much more time over water, and could easily become a hurricane.

The forecast track reasoning remains unchanged. A trough over the SE US is eroding the western periphery of the Bermuda High, and is allowing Isaac to begin moving northwestward. The average heading from the last 4 recon fixes was 305 degrees. This should take Isaac across the greater Antilles and in the general direction of Florida during the next 3 days. The forecast track has been shifted a bit westward due to the southward reformation of Isaac’s center, which has placed him well southwest of where he was expected to be this morning. The track now takes Isaac up the Florida Penisula. This track is still slightly to the east of the model consensus. The models have been shifting slightly eastward with each run ever since recon G-IV data was injected into their routines last night, and they now show a much more reasonable-looking recurvature into the Florida panhandle and then Georgia and the Carolinas, as opposed to the nonsensical northwest track across the Mississippi River that they showed last night. I believe some eastward adjustments of the models are still likely to occur with time. It should be noted that there is still great uncertainty in the track due to the crossing of the Caribbean mountains, since they are known to jerk storms around in unpredictable fashions, and could cause am abrupt shift in the track at any time. The entire eastern gulf coast, Florida, and the other southeastern states should monitor Isaac closely, both for direct landfall impacts, and heavy rainfall afterwards.

Elsewhere…Joyce is sheared and weak, and is not an imminent threat to land. She will be moving northwest in the general direction of Bermuda during the next 4 days.

We shall see what happens!