Isaac expected to cross the Florida Keys as a hurricane by late Sunday (26)
Sunday, August 26, 2012 7:56 am
by Rob Lightbown of Crown Weather
Tropical Storm Isaac:
Tropical Storm Isaac looks pretty ragged on satellite imagery this morning with 
some deeper thunderstorm activity noted on the north and east sides of the storm. This is deceptive, however, as reconnaissance aircraft have found central pressures of 995 millibars and 65 mph winds. The overall track forecast from the various forecast guidance seem to be in good agreement that Isaac will track across the Florida Keys, likely between Key West and Marathon late this afternoon with hurricane conditions expected across the Florida Keys and southwest Florida, including Naples and Marco Island this afternoon into tonight.
So, by Monday morning, I expect that Isaac will be located over the southeastern Gulf of Mexico, approximately 100 miles northwest of Key West. Isaac is expected to track northwestward across the 
eastern Gulf of Mexico where it will strengthen on Monday into Tuesday. The forecast guidance from Monday through Tuesday start to diverge quite a bit and the various guidance cannot agree on a final landfall location on the northern Gulf Coast. The reason for the divergence in the guidance is due to how they are forecasting the track of a trough of low pressure and a high pressure ridge that is located to the west and to the east of this trough. The GFS and Canadian model guidance forecast that Isaac will miss this trough and that the high pressure ridge will steer Isaac towards a landfall in southeastern Louisiana on Wednesday afternoon. The European and NAM model guidance forecast enough of a gap in the ridges of high pressure that leads to a turn to the north and a landfall somewhere between Mobile Bay and Pensacola and Fort Walton Beach.
Taking a closer look at the European model guidance, yesterday’s forecast runs of this model showed a forecast of Isaac making landfall near Apalachicola. The most recent forecast run of the European model shows a landfall very close to Mobile Bay; so, it seems the European model may be edging westward towards the idea of a landfall somewhere between New Orleans and Pensacola.
The ensembles of the GFS and European models have a forecast track that is in-between the operational models with the GFS ensemble forecasting a landfall near Gulfport, Mississippi early Wednesday morning and the European ensemble guidance forecasting a landfall near the Mississippi-Alabama stateline.
So, my thinking as of this morning is to shift the forecast track of Isaac westward as the trough of low pressure may not be strong enough to fully capture the storm. My forecast is close to the European model guidance, the consensus track guidance and is close to the latest NHC forecast track and takes Isaac across the western side of Mobile Bay just after midnight Tuesday night as a 105-110 mph Category 2 hurricane.
It should be pointed out that should the GFS model forecast of the ridge of high pressure steering Isaac instead of the storm tracking into the trough of low pressure turn out correct, then further adjustments in the forecast track to the west towards central and southeastern Louisiana may be needed. All interests from coastal Louisiana to the Florida Panhandle need to closely monitor the progress and forecast track of Isaac. Hurricane Watches are now in effect for the entire coasts of Mississippi and Alabama as well as the Florida Panhandle as far east as Panama City. These Hurricane Watches may need to be extended westward across coastal Louisiana, including New Orleans at some point today.
Impacts From Isaac: Rainfall Impact: Total rainfall amounts of 5 to 10 inches are expected across the Florida Keys and south Florida today into tonight. Much of the central and western Florida Peninsula will receive between 3 and 7 inches of rainfall from later today through all of Monday and into Tuesday. As for the northern Gulf coast, 5 to 10 inches of total rainfall is likely from southeastern Louisiana eastward to the Florida Panhandle from Tuesday through Wednesday.
Wind Impact: Hurricane conditions are expected across southwest Florida, including Naples and Marco Island as well as the Florida Keys this afternoon through tonight. Tropical storm force winds will begin to affect southwest Florida and the Florida Keys within the next couple of hours. Tropical storm conditions are already occurring in parts of southeastern Florida and will spread up Florida’s East Coast a little later this morning. Along Florida’s West Coast, tropical storm conditions are expected tonight into Monday.
As for the northern Gulf Coast, hurricane conditions seem likely along the coasts of Mississippi, Alabama and the western Florida Panhandle starting on Tuesday afternoon and continuing through Tuesday night before slowly subsiding Wednesday morning. It needs to be pointed out that hurricane conditions may affect southeastern Louisiana should the track of Isaac shift further to the west.
Storm Surge Impact: The following storm surges can be expected:
From Crystal River through Florida’s Big Bend: 4 to 7 Feet. Southwestern Florida: 4 to 7 Feet. Tampa Bay: 3 to 5 Feet. Southeastern Florida and the Florida Keys: 1 to 3 Feet.
Across the Florida Keys and southwestern Florida, all storm preparations should already be complete; this includes the securing of your property and boats. The following shelters are now open that will accommodate people who need to go for a safe place from the storm:
Key West High School on Flagler Avenue in Key West. Sugarloaf school on upper Sugarloaf Key. Stanley switlik school in Marathon. Coral shores High School in Islamorada.
If you live in a mobile home, or on a boat or in a low-lying area, I strongly urge you to go to a shelter for your own safety.
The Key West International Airport and the Florida Keys Marathon Airport are closed. The port of Key West is closed.
I will continue to monitor the progress of Isaac extremely closely and will continue to have frequent updates on the storm.
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