ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM HURRICANE ISABEL DISCUSSION NUMBER 20 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 PM EDT WED SEP 10 2003 SATELLITE INTENSITY ESTIMATES ARE A CONSENSUS T6.5...127 KT...AND SO THE ADVISORY INTENSITY IS INCREASED TO 125 KT. THE MOST RECENT 3-HR AVERAGE OBJECTIVE DVORAK INTENSITY ESTIMATE WAS JUST BELOW 130 KT. ALTHOUGH THERE IS CURRENTLY NO UPPER-LEVEL OUTFLOW TO THE NORTH... THERE ARE TWO VERY EFFICIENT OUTFLOW CHANNELS OPERATING TO THE WEST AND EAST OF THE HURRICANE. ISABEL IS EXPECTED TO REMAIN A MAJOR HURRICANE THROUGHOUT THE FORECAST PERIOD. WIND RADII HAVE BEEN ADJUSTED SLIGHTLY INWARD BASED ON A RECENT QUIKSCAT PASS. THE INITIAL MOTION ESTIMATE IS 270/9. THE WESTWARD TRACK IS THE RESULT OF A MID TO UPPER-LEVEL HIGH CURRENTLY LOCATED NORTH OF ISABEL NEAR 30N. THIS HIGH IS FORECAST BY GLOBAL MODELS TO SLIDE WESTWARD WITH ISABEL FOR THE NEXT TWO TO THREE DAYS...AND MAINTAIN ISABEL ON A TRACK JUST A BIT NORTH OF DUE WESTWARD. BY DAYS 4 AND 5 OF THE FORECAST PERIOD...NEARLY ALL OF THE GLOBAL MODEL GUIDANCE SLOWS THE WESTWARD PROGRESSION OF THE HIGH AND ALLOWS THE TRACK TO SLOW AND BEND SLIGHTLY TO THE RIGHT. THE FOUR MAIN TRACK MODELS... THE GFDL...GFS...UKMET...AND NOGAPS...ARE NOW IN VERY GOOD AGREEMENT THROUGH DAY 5...AS THE GFS HAS SHIFTED SUBSTANTIALLY NORTHWARD FROM ITS PREVIOUS RUN. THE OFFICIAL FORECAST HAS BEEN ADJUSTED NORTHWARD TO BE IN BETTER AGREEMENT WITH THE CURRENT GUIDANCE...BUT IS STILL ON THE SOUTH EDGE OF THE GUIDANCE ENVELOPE. THE ONE OUTLIER IS THE ECMWF...A MODEL VERY SKILLED AT FORECASTING LARGE-SCALE ATMOSPHERIC PATTERNS...WHICH IS SUBSTANTIALLY SOUTH OF THE OTHERS IN BRINGING ISABEL NEAR THE EXTREME SOUTHEASTERN BAHAMAS BY DAY 5. IT IS NATURAL TO WANT TO SPECULATE ON THE FORECAST TRACK BEYOND 5 DAYS...BUT IT SIMPLY IS NOT POSSIBLE TO DO SO WITH CONFIDENCE. THE GLOBAL MODELS BEGIN TO DIVERGE MARKEDLY ON HOW MUCH RIDGING WILL REMAIN OFF THE U.S. SOUTHEAST COAST BY DAY 5. THE EXTENT AND ORIENTATION OF THIS RIDGING WILL BE CRUCIAL IN DETERMINING THE POTENTIAL IMPACTS TO THE BAHAMAS AND THE EASTERN UNITED STATES. GIVEN THAT ISABEL IS STILL SEVERAL DAYS AWAY FROM THESE AREAS...THIS WOULD BE A GOOD TIME FOR RESIDENTS TO REVIEW THEIR PREPAREDNESS PLANS IN CASE ISABEL BECOMES A DIRECT THREAT. THE FIRST RECONNAISSANCE AIRCRAFT FLIGHT INTO ISABEL IS SCHEDULED FOR FRIDAY AFTERNOON. MISSIONS TO SAMPLE THE SYNOPTIC ENVIRONMENT OF ISABEL ARE ALSO SCHEDULED TO BEGIN ON FRIDAY. FORECASTER FRANKLIN FORECAST POSITIONS AND MAX WINDS INITIAL 11/0300Z 21.1N 52.8W 125 KT 12HR VT 11/1200Z 21.2N 54.3W 125 KT 24HR VT 12/0000Z 21.4N 56.2W 125 KT 36HR VT 12/1200Z 21.7N 58.0W 120 KT 48HR VT 13/0000Z 22.0N 60.0W 120 KT 72HR VT 14/0000Z 23.0N 64.0W 115 KT 96HR VT 15/0000Z 24.0N 68.0W 115 KT 120HR VT 16/0000Z 25.0N 71.5W 115 KT NNNN
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