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#113738 (Received by flhurricane at: 11:11 AM 30.Sep.2006) TCDAT4 HURRICANE ISAAC DISCUSSION NUMBER 12 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL092006 1100 AM EDT SAT SEP 30 2006 SATELLITE IMAGES INDICATE THAT ISAAC FORMED A RAGGED EYE SHORTLY AFTER THE PREVIOUS ADVISORY. A HIGH RESOLUTION QUIKSCAT PASS NEAR 1000 UTC SHOWED ONE BELIEVABLE WIND SPEED OF 63 KT. HOWEVER THE SATELLITE PRESENTATION HAS IMPROVED SOMEWHAT IN ORGANIZATION SINCE THAT TIME. AFTER BECOMING OBSCURED A FEW HOURS AGO... THE EYE HAS BECOME A LITTLE BETTER-DEFINED IN VISIBLE IMAGERY. IN ADDITION... A SATELLITE ESTIMATE FROM TAFB IS AT T4.0... 65 KT... WHILE CIMSS/CIRA AMSU ESTIMATES ARE BOTH ANALYZING ISAAC WITH 64 KT WINDS. THEREFORE ISAAC IS UPGRADED TO A HURRICANE WITH 65 KT WINDS... THE FIFTH HURRICANE OF THE SEASON. THE ENVIRONMENT LOOKS CONDUCIVE FOR A LITTLE STRENGTHENING AS ISAAC REMAINS IN A RELATIVELY LIGHT SHEAR AREA AND OVER SUFFICIENTLY WARM WATER TEMPERATURES. HOWEVER... SOUTHWESTERLY SHEAR SHOULD BEGIN TOMORROW DUE TO AN APPROACHING UPPER TROUGH AND LIMIT ANY FURTHER INTENSIFICATION. THE INTENSITY FORECAST IS A BLEND OF THE FSU SUPERENSEMBLE... GFDL AND THE PREVIOUS FORECAST. ISAAC IS EXPECTED TO REMAIN A STRONG EXTRATROPICAL LOW BEFORE ITS EVENTUAL ABSORPTION BY A LARGER LOW. THE INITIAL MOTION ESTIMATE IS 300/6. A GRADUAL RIGHTWARD TURN SHOULD OCCUR DURING THE NEXT 24 HOURS AS ISAAC ROUNDS THE WESTERN PORTION OF THE SUBTROPICAL RIDGE. THEREAFTER THE CYCLONE SHOULD BE ACCELERATING NORTHWARD AHEAD OF A DEEP MIDDLE-LATITUDE TROUGH OVER THE WESTERN ATLANTIC OCEAN. MODEL GUIDANCE REMAINS IN GOOD AGREEMENT AND THE OFFICIAL FORECAST IS BASICALLY AN UPDATE OF THE PREVIOUS ONE. ISAAC SHOULD ENCOUNTER A MORE BAROCLINIC ENVIRONMENT IN 36-48 HOURS... WHICH IS EXPECTED TO CAUSE IT TO TRANSITION INTO AN EXTRATROPICAL CYCLONE BY 3 DAYS. GLOBAL MODELS ARE FORECASTING THE REMNANTS OF ISAAC TO BE ABSORBED BY A LARGER EXTRATROPICAL LOW NEAR THE 96 HOUR TIME FRAME. FORECAST POSITIONS AND MAX WINDS INITIAL 30/1500Z 30.9N 58.7W 65 KT 12HR VT 01/0000Z 31.6N 59.6W 70 KT 24HR VT 01/1200Z 33.4N 60.5W 75 KT 36HR VT 02/0000Z 36.8N 60.5W 70 KT 48HR VT 02/1200Z 41.5N 59.0W 60 KT...EXTRATROPICAL 72HR VT 03/1200Z 50.0N 50.0W 50 KT...EXTRATROPICAL 96HR VT 04/1200Z...ABSORBED $$ FORECASTER BLAKE/STEWART |