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| #536933 (Received by flhurricane at: 5:05 PM 25.Aug.2012) TCDAT4 TROPICAL STORM ISAAC DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 500 PM EDT SAT AUG 25 2012 THE CENTER OF ISAAC IS CURRENTLY MOVING ALONG THE NORTH COAST OF EASTERN CUBA. THE SATELLITE APPEARANCE IS SOMEWHAT DISORGANIZED... WITH THE MAIN CONVECTIVE MASS 50 N MI OR MORE EAST OF THE LOW-LEVEL CENTER. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT HAS REPORTED 850 MB FLIGHT-LEVEL WINDS OF 56 KT TO THE NORTHEAST OF THE CENTER...WITH RELIABLE-LOOKING SFMR SURFACE WIND DATA NEAR 50 KT. BASED ON THIS...THE INITIAL INTENSITY REMAINS 50 KT. THE CENTRAL PRESSURE OF 997 MB IS BASED ON A COMBINATION OF AIRCRAFT DATA AND CUBAN SURFACE OBSERVATIONS. THE INITIAL MOTION IS NOW 310/18. ISAAC IS CURRENTLY PART OF A LARGE LOW/MID-LEVEL LOW PRESSURE SYSTEM COVERING THE NORTHWESTERN CARIBBEAN SEA AND THE ADJACENT LAND AND OCEAN AREAS. THIS LOW PRESSURE AREA HAS A SECOND VORTICITY CENTER BETWEEN JAMAICA AND THE CAYMAN ISLANDS...AND FOR THE NEXT 24-36 HR ISAAC AND THIS CENTER WILL LIKELY ROTATE AROUND EACH OTHER. BASED ON THIS EXPECTATION... THE FORECAST TRACK SHOWS ISAAC MOVING NORTHWESTWARD FOR 12 HR OR SO...FOLLOWED BY A TURN TOWARD THE WEST-NORTHWEST. IT IS POSSIBLE THE STORM COULD MAKE A SHARPER TURN THAN FORECAST...AS THE UKMET IS SHOWING AN ALMOST DUE WEST MOTION BETWEEN THE FLORIDA KEYS AND CUBA NEAR THE 36 HR POINT. THE EARLY PART OF THE FORECAST TRACK IS SHIFTED A LITTLE TO THE LEFT OF THE PREVIOUS FORECAST...BUT STILL LIES TO THE RIGHT OF THE CONSENSUS MODELS AND THE BULK OF THE DYNAMICAL MODELS. AFTER 36 HR...ISAAC SHOULD BREAK FREE OF OR ABSORB THE REST OF THE LOW...WITH THE SUBTROPICAL RIDGE TO THE EAST BECOMING THE DOMINANT STEERING INFLUENCE. THIS SHOULD ALLOW THE STORM TO GRADUALLY TURN TOWARD THE NORTHWEST AND NORTH OVER THE EASTERN AND NORTHERN GULF OF MEXICO...WITH AN EVENTUAL LANDFALL ALONG THE NORTHERN GULF COAST IN 72-96 HR. WHERE THIS MIGHT OCCUR IS STILL RATHER UNCERTAIN...WITH THE TRACK GUIDANCE SPREAD BETWEEN SOUTHEASTERN LOUISIANA AND THE CENTRAL FLORIDA PANHANDLE. THIS PART OF THE TRACK FORECAST LIES IN THE CENTER OF THE GUIDANCE ENVELOPE NEAR THE CONSENSUS MODELS AND IS SIMILAR TO THE PREVIOUS FORECAST. A COMBINATION OF LIGHT WESTERLY VERTICAL WIND SHEAR AND LAND INTERACTION SHOULD AT LEAST SLOW INTENSIFICATION FOR THE NEXT 12 HR. AFTER THAT...THE SHEAR SHOULD DIMINISH WHILE THE CYCLONE REACHES OPEN WATER. THIS SHOULD ALLOW ISAAC TO GRADUALLY STRENGTHEN INTO A HURRICANE NEAR THE FLORIDA KEYS OR OVER THE SOUTHEASTERN GULF OF MEXICO. THE NEW INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS FORECAST AND IS NEAR OR A LITTLE ABOVE THE INTENSITY CONSENSUS. IT SHOULD BE NOTED THAT THE GLOBAL MODELS ARE FORECASTING A VERY FAVORABLE PATTERN OF UPPER-LEVEL WINDS OVER THE NORTHERN GULF OF MEXICO BY 72 HR. SHOULD THIS VERIFY AND SHOULD ISAAC ESTABLISH AN INNER CORE...THE CYCLONE COULD BE SIGNIFICANTLY STRONGER THAN CURRENTLY FORECAST. IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK OF ISAAC DUE TO THE UNCERTAINTIES IN THE FORECAST AND THE FACT THAT ISAAC HAS A LARGE AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED WITH IT. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 21.3N 76.0W 50 KT 60 MPH 12H 26/0600Z 22.6N 78.0W 55 KT 65 MPH 24H 26/1800Z 24.1N 80.6W 60 KT 70 MPH 36H 27/0600Z 25.2N 82.7W 65 KT 75 MPH 48H 27/1800Z 26.5N 84.3W 75 KT 85 MPH 72H 28/1800Z 29.0N 86.0W 85 KT 100 MPH 96H 29/1800Z 31.5N 86.0W 55 KT 65 MPH...INLAND 120H 30/1800Z 33.5N 85.5W 25 KT 30 MPH...INLAND $$ FORECASTER BEVEN |
