Written by Amy Godsey, Florida State Meteorologist Monday, 27 August 2012 08:25
5am Monday, 8/27/12 Summary:
After moving around the FL Keys and Dry Tortugas overnight, at 5am EDT Sunday, Tropical Storm Isaac was located in the eastern Gulf of Mexico about 180 miles southwest of Ft. Myers, or approximately 315 miles south-southeast of Apalachicola, FL.
There continues to be an unusual high degree of uncertainty in the track forecast past the next 24 hours. Some of the more reliable models are still to the east while others are trending further westward with time, keeping the range of possibilities between the Florida Panhandle and northeast Texas. The models that still show a more eastward track have Isaac being picked up by a storm system and trough moving into the Tennessee Valley, while the westward models show that the trough will be too weak and will bypass Isaac completely, instead, being steered by high pressure westward.
The official NHC forecast has sped up slightly and shifted west, taking Tropical Storm Isaac south of the Florida Panhandle today and tomorrow, then making landfall in southeastern Louisiana.
Maximum sustained winds remain near 65 mph. Isaac has a rather large circulation and no well-defined core. In addition, an upper level low pressure area near Isaac for the past few days has resulted in some increased shear. Although Isaac is moving through very warm waters, the lack of definition and shear will prohibit any rapid strengthening.
Isaac is still forecast to become a hurricane later today and gradually strengthen until landfall on Tuesday night.
Isaac remains a large storm, and tropical storm force winds extend as far as 240 miles from the center. Due to the large wind field associated with Isaac, effects will continue to be felt far away from the center.
A tropical wave and associated area of low pressure in the eastern Atlantic, designated as invest area 97L, is slowly trying to organize. However, environmental conditions are forecast to become increasingly hostile for development as it moves northwest at 10-15mph.
The National Hurricane Center is now forecasting a medium (30%) chance of becoming a tropical depression within the next 2 days.
A new tropical wave emerging from western Africa may begin to organize over the next several days. There is currently only a 10% chance of becoming a tropical cyclone within the next 48 hours, but chances may increase in a few days as it moves west around 10-15mph.
Watches and Warnings Issued for Florida:
Hurricane Warning – Destin westward to Morgan City, Louisiana. This includes the FL counties of Escambia, Santa Rosa, Okaloosa.
Hurricane Watch – (Florida Panhandle) Indian Pass to Destin. This includes the counties of Gulf, Bay, Walton.
Tropical Storm Warning – (Florida Panhandle) Destin to Suwannee River; (West Coast) Tarpon Springs to Florida Bay; Florida Keys to Ocean Reef. This includes the counties of Gulf, Bay, Walton, coastal Franklin, coastal Wakulla, coastal Jefferson, coastal Taylor, coastal Dixie, Polk, Hillsborough, Pinellas, Manatee, Sarasota, Hardee, DeSoto, Highlands, Charlotte, Lee, coastal Collier, far south Miami-Dade, Monroe.
Although wind probabilities are decreasing, the large nature of Isaac could still produce a greater than 40% chance of receiving tropical storm force winds along coastal Southwest Florida, and much of the Florida Panhandle. Tampa currently has a 28% chance of receiving tropical storm force winds and Tallahassee has a 27% chance. All of Florida now has a less than 5% chance of seeing hurricane force winds.
Tropical storm force winds will exit South Florida later this morning and could affect coastal areas of the Panhandle later this evening through the overnight hours into Tuesday. Tropical storm conditions could linger over the western Panhandle for several hours, from Monday night through Wednesday morning.
Although sustained tropical storm force winds for any significant length of time is low in the Florida Big Bend, gusts to tropical storm force are possible. However, large storm tide heights are still expected in Apalachee Bay and a Tropical Storm Watch includes the hazard for wind and surge.
Heavy rainfall will continue to affect much of Central and South Florida today as the outer bands of Isaac rotate through the Peninsula. An estimated 2-4 inches of rainfall has fallen over much of South Florida since Sunday morning. Higher amounts of 4-8 inches have fallen over some areas of Broward County, with as much as 9-13 inches in parts of Palm Beach County.
An additional 1-3 inches will be possible over West Central and South Florida today. A Flood Watch is in effect for South Florida until 8pm tonight. Gusty winds will still be capable of knocking down trees in saturated ground.
Over the next 3 days, areas of the Florida Big Bend may receive up to 4 inches, with many Panhandle areas forecast to receive between 3 and 9 inches and locally higher amounts to 15 inches.
Storm tide (surge + tide) heights may reach 3-5 feet along the southwest coast of Florida, 2-3 feet along West Central Florida (Tampa Bay northward), and 3-5 feet in Apalachee Bay and along the Florida Panhandle. However, higher surges up to 7-8 feet are possible near Perdido Key and at the head of Apalachee Bay.
Large waves statewide will result in a high risk of rip currents. A High Surf Advisory is in effect from Nassau County to Martin County.
A Tornado Watch is in effect for South Florida until 9am. Additional watches are possible. The Storm prediction Center has placed much of the state in a slight risk for severe weather on Monday and Tuesday and for Northwest Florida on Wednesday.
More information on Tropical Storm Isaac and 97L can be found at www.nhc.noaa.gov.
Click here to view storm related graphics and images. Another update will be issued Monday afternoon.
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