ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM HURRICANE ISABEL DISCUSSION NUMBER 23 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 PM EDT THU SEP 11 2003 ISABEL HAS CONTINUED TO INTENSIFY TODAY. DVORAK T-NUMBERS FROM ALL 3 AGENCIES...TAFB...SAB...AND AFWA ARE NOW 7.0 AND OBJECTIVE T-NUMBERS ARE ALSO ABOUT THE SAME VALUE. THIS SUPPORTS A CURRENT INTENSITY ESTIMATE OF 140 KT...A CATEGORY 5 ON THE SAFFIR-SIMPSON HURRICANE SCALE. HURRICANES RARELY MAINTAIN SUCH STRENGTH FOR VERY LONG...AND ISABEL MAY NOT STAY A CAT 5 FOR EVEN AS LONG AS SHOWN HERE. THERE IS AN UPPER-LEVEL CYCLONE ABOUT 15 DEGREES TO THE WEST-NORTHWEST OF THE HURRICANE BUT THIS SYSTEM APPEARS TO BE NARROWING AND IF THIS TREND CONTINUES...IT SHOULD NOT HAVE MUCH OF AN IMPACT ON THE INTENSITY OF ISABEL. ANOTHER POSSIBLE FACTOR IS THE COOLED SST WAKE PRODUCED BY HURRICANE FABIAN IN THE VICINITY OF 63W. SINCE THERE DO NOT TO BE ANY MAJOR INHIBITING FACTORS IN THE ENVIRONMENT...INTERNAL DYNAMICS SUCH AS EYEWALL REPLACEMENT CYCLES WILL PROBABLY HAVE THE GREATEST INFLUENCE ON INTENSITY CHANGE. THE OFFICIAL FORECAST ASSUMES THAT WE WILL CONTINUE TO HAVE A MAJOR HURRICANE ON OUR HANDS THROUGHOUT THE FORECAST PERIOD. MOTION CONTINUES AT ABOUT 280/8...ALONG WITH SOME MINOR TROCHOIDAL WOBBLES. A DEEP-LAYER HIGH PRESSURE AREA TO THE NORTH OF ISABEL IS LIKELY TO MAINTAIN THE SLOW WESTWARD TO WEST-NORTHWESTWARD STEERING OVER THE NEXT SEVERAL DAYS. THE CURRENT NHC FORECAST IS SOMEWHAT SLOWER THAN THE PREVIOUS ONE...BUT FASTER THAN THE GUNA CONSENSUS. THIS IS FAIRLY CLOSE TO THE LATEST U.K. MET OFFICE TRACK. THE LATTER MODEL IS THE WESTERNMOST OF THE GUIDANCE SUITE. THE BIG QUESTION CONTINUES TO BE WHAT WILL HAPPEN BEYOND THE 5-DAY FORECAST PERIOD. IT IS STILL IMPOSSIBLE TO STATE WITH ANY CONFIDENCE WHETHER A SPECIFIC AREA ALONG THE U.S. COAST WILL BE IMPACTED BY ISABEL. THIS WILL LIKELY DEPEND ON THE RELATIVE STRENGTH AND POSITIONING OF A MID-TROPOSPHERIC RIDGE NEAR THE EAST COAST AND A MID-LATITUDE TROUGH TO THE WEST OR NORTHWEST AROUND THE MIDDLE OF NEXT WEEK. UNFORTUNATELY...WE HAVE LITTLE SKILL IN PREDICTING THE EVOLUTION OF STEERING FEATURES AT THESE LONG RANGES. FORECASTER PASCH FORECAST POSITIONS AND MAX WINDS INITIAL 11/2100Z 21.6N 55.3W 140 KT 12HR VT 12/0600Z 21.7N 56.7W 140 KT 24HR VT 12/1800Z 21.9N 58.6W 135 KT 36HR VT 13/0600Z 22.4N 60.5W 130 KT 48HR VT 13/1800Z 22.9N 62.3W 125 KT 72HR VT 14/1800Z 24.0N 65.5W 115 KT 96HR VT 15/1800Z 25.0N 68.5W 115 KT 120HR VT 16/1800Z 26.0N 71.5W 115 KT NNNN
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