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| #4298 (Received by flhurricane at: 4:47 PM 11.Aug.2004) TCDAT2 TROPICAL STORM BONNIE DISCUSSION NUMBER 15 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 PM EDT WED AUG 11 2004 RECONNAISSANCE AND SATELLITE DATA INDICATE BONNIE HAS MADE THE EXPECTED SHARP TURN TO THE NORTHEAST. HOWEVER...IT HAS BEEN DIFFICULT FOR THE FLIGHT CREW TO ASSESS A SOLID CENTER LOCATION DUE TO THE MULTIPLE CONVECTIVE BURSTS AND SMALL MESOVORTICES THAT HAVE BEEN SPINNING UP AND SPINNING DOWN. THE ADVISORY POSITION IS A COMPROMISE OF THE LAST 4 RECON POSITIONS...SATELLITE ESTIMATES... AND CONTINUITY WITH THE PREVIOUS FORECAST TRACK AND THE LATEST MODEL FORECAST TRACKS. THE ADVISORY PRESSURE IS LOWER THAN THE RECON REPORTS AND IS BASED ON NEARBY BUOY REPORTS AND REDUCING THE PRESSURE ABOUT 10 MB ASSUMING A GRADIENT A WIND OF 50-55 KT. A SUBSEQUENT LATE REPORT FROM NOAA BUOY 42001 INDICATED A GUST TO 66 KT...WHICH WOULD SUGGEST A SURFACE WIND OF ABOUT 55 KT. REDUCTION OF A 72-KT FLIGHT-LEVEL WIND ALSO YIELDS A 57 KT SURFACE WIND. THE INITIAL MOTION ESTIMATE IS 040/10. BONNIE HAS CLEARLY MADE THE TURN TO THE NORTHEAST NOW THAT THE CYCLONE IS BEING DIRECTLY INFLUENCED BY AN APPROACHING SHORTWAVE TROUGH ALONG THE TEXAS COAST. WATER VAPOR IMAGERY AND 18Z UPPER-AIR OBSERVATIONS SUGGEST THAT THE SUBTROPICAL RIDGE TO THE SOUTH OF BONNIE LOCATED OVER SOUTHERN FLORIDA IS BEGINNING TO SHIFT SLOWLY NORTHWARD. THIS SHOULD FURTHER ENSURE THAT BONNIE WILL GENERALLY MOVE IN A NORTHEASTWARD DIRECTION. THE NHC MODEL GUIDANCE REMAINS IN GOOD AGREEMENT ON THIS DEVELOPING SCENARIO AND SUGGESTS LANDFALL IN ABOUT 18 HOURS ALONG THE CENTRAL COAST OF THE FLORIDA PANHANDLE. AFTER THE EARLIER TREMENDOUS BURST OF DEEP CONVECTION...THE CONVECTION HAS LEVELED OFF AND SO HAVE THE WIND SPEEDS. HOWEVER... THE OVERALL LOW-LEVEL WIND FIELD AND CONVECTIVE PATTERN HAS IMPROVED THIS AFTERNOON...ESPECIALLY WHEN COMPARED TO 24 HOURS AGO. BONNIE IS EXPECTED TO PASS OVER OR JUST NORTH OF A WARMER GULF EDDY IN ABOUT 12 HOURS...COINCIDENTALLY THE SAME TIME AS THE NIGHT TIME CONVECTIVE MAXIMUM PERIOD. THE STRONG SOUTHWESTERLY UPPER-LEVEL SHEAR IS EXPECTED TO HOLD OFF UNTIL ABOUT 18 HOURS AND NORTH OF 29N LATITUDE...SO BONNIE MAY BECOME A LOW END CATEGORY 1 HURRICANE BY THURSDAY MORNING. AFTER THAT...HOWEVER...35-50 KT 200 MB WINDS MAY BRING ABOUT WEAKENING JUST BEFORE LANDFALL. HOWEVER...UNCERTAINTY IN THE TIMING OF THIS WEAKENING REQUIRES THAT A HURRICANE WARNING BE ISSUED FOR THE FLORIDA PANHANDLE AND BIG BEND AREA. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 11/2100Z 26.7N 89.3W 55 KT 12HR VT 12/0600Z 28.2N 87.3W 65 KT 24HR VT 12/1800Z 30.8N 84.7W 50 KT...INLAND 36HR VT 13/0600Z 34.1N 81.3W 35 KT...INLAND 48HR VT 13/1800Z 38.3N 77.0W 30 KT...INLAND EXTRATROPICAL 72HR VT 14/1800Z 48.0N 67.0W 30 KT...INLAND EXTRATROPICAL 96HR VT 15/1800Z...ABSORBED BY FRONTAL ZONE |
