Friday, August 24, 2012

Friday afternoon update on Tropical Storm Isaac

Last night, I wrote a pretty detailed blog on Tropical Storm Isaac.  If you wish to review it, click here. I won't go into quite as much detail today, but there have been a couple of fairly noteworthy developments since last night.

1. Intensity - As expected, the appearance of Isaac has improved and that has been reflected in the overall strength of the storm.  As of the 4pm update from the National Hurricane Center, maximum sustained wind is up to 65 mph and minimum central pressure has dropped to 994 mb. Little additional strengthening is expected until after the storm passes Cuba.  Some weakening is likely if it passes over enough land (esp. Cuba).

2. Motion - After moving generally westerly for a couple of days, Isaac made it's turn to the northwest as it moves into a weakness in the high pressure ridge it was moving to the south of previously. This sets it's course across Haiti and Cuba as it gets ready to head into generally towards south Florida this weekend.

Mid-afternoon Friday visible satellite image of Isaac and it's approximate forecast path. Note the better organization of the storm than shown in yesterday's blog post.
3. Forecast track - Watching each run of the model tracks is rather interesting.  After overnight observations of the upper level pattern made by a NOAA jet were ingested into the models, the tracks stopped their incessant westward shift and have now started sliding back to the east.  While the central Gulf Coast from Mobile to Apalachicola needs to continue to remain on high alert, there is now increasing worry for the Florida peninsula.  In fact, the 4pm "official" track from the Hurricane Center (below) moves the forecast path nearly over Key West and on to a landfall near Pensacola on Tuesday. However the forecaster's discussion leaves open the possibility of a further eastward shift in the track of models continue to converge on that solution.

Friday afternoon computer model tracks showing potential paths. All eyes are on the FL panhandle, though south Florida and the Florida Gulf Coast need to also be on high alert. 
4pm CDT "official" hurricane track from NHC. Courtesy Weather Underground. Any more rightward (east) shift in the first day or so will place much of South FL in a higher risk.
4.  Affects - This eastward model shift means that a much larger population is now potentially in harm's way, including (once again) Tampa and the RNC next week, as well as much of south Florida. Depending on how close the storm moves to the west coast of Florida and how much (if any) of south Florida the storm moves over, the ultimate strength of Isaac could vary greatly. As most people know, more warm water = stronger storms. A direct path across the Gulf to MS/AL/FL panhandle could bring a much stronger storm than one that crosses south Florida and skirts the west coast of the peninsula.  Time will tell and many more model runs lie between now and any potential landfall.

South Florida in particular needs to start preparing as Tropical Storm Watches have been issued from south of Fort Myers around the southern tip of the state to north of West Palm Beach, including all inland areas from Lake Okeechobee south. There is enough warm water between the current location and the tip of Florida (and less land area to traverse) that a hurricane-strength storm would cause major issues for places from Fort Myers to Fort Lauderdale.  NHC leaves open the possibility of Hurricane Watches for south Florida with any further eastward shift in the track.

We'll continue to monitor developments, provide bits of useful information on our social feeds (listed below), and update the blog as necessary and warranted.  Visit the MWN Tropical page for the latest information.

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