Tropical Storm BONNIE

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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
 
 
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