ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM HURRICANE ISABEL DISCUSSION NUMBER 30 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 AM EDT SAT SEP 13 2003 ISABEL HAS COMPLETED AN EYEWALL REPLACEMENT CYCLE BASED ON A 13/1102Z SSMI OVERPASS SHOWING A CLOSED 35 NMI DIAMETER EYE. THE INTENSITY IS MAINTAINED AT 130 KT BASED ON CONTINUITY WITH THE PREVIOUS DATA...A CONSENSUS SATELLITE INTENSITY ESTIMATE OF 127 KT...RAW ODT VALUES OF T6.5...OR 127 KT...AND THE FACT THAT THE EYE HAS CLEARED OUT NICELY AND SURROUNDING EYEWALL CLOUD TOPS HAVE COOLED TO -70C AND COLDER ONCE AGAIN. NEXT RECON MISSION IS AT 18Z. THE INITIAL MOTION IS 280/08. OVER THE PAST 72 HOURS...ISABEL HAS BEEN MOVING AT 275 DEGREES. THE HURRICANE MADE A SLIGHT NORTHWARD WOBBLE DURING THE EARLIER EYEWALL REPLACEMENT CYCLE...BUT IT NOW APPEARS TO HAVE RESUMED A 275-280 DEGREES MOTION. ALL OF THE GLOBAL AND REGIONAL MODELS HAVE HAD A DISTINCT RIGHT-OF-TRACK BIAS BY AS MUCH AS 10 DEGREES...AND EACH MODEL RUN HAS BEEN A LITTLE FARTHER WEST AND SLOWER. THE EXCEPTION IS THE 06Z GFDL RUN WHICH MADE A MAJOR SHIFT WESTWARD BY MORE 200 NMI IN THE LATER FORECAST PERIODS ...WHILE THE 06Z NOGAPS MODEL ACCELERATED ISABEL AND HAS THE HURRICANE ONSHORE THE SOUTHEAST COAST OF NORTH CAROLINA IN 120 HOURS. HOWEVER...THE MODEL CONSENSUS IS SLOWER AND FARTHER WEST BEFORE A TURN TO THE NORTHWEST OCCURS IN THE LATER PERIODS. THE MODELS OBVIOUSLY HAVE NOT BEEN HANDLING THE STRONG RIDGING TO THE NORTH OF ISABEL VERY WELL. THIS MAY BE DUE TO THE OUTFLOW ON THE NORTH SIDE BEING DRAWN NORTHWARD AND SINKING ALONG 30N-33N...WHICH MAY HAVE HELPED TO STRENGTHEN THE SUBTROPICAL RIDGE. WATER VAPOR IMAGERY INDICATES THIS PATTERN HAS PERSISTED FOR MORE THAN 72 HOURS AND CONTINUES TO SHIFT WESTWARD WITH ISABEL. THEREFORE...A GENERAL WESTWARD MOTION SHOULD CONTINUE FOR ANOTHER 36 HOURS OR SO. AFTERWARDS...THERE REMAINS CONSIDERABLE DIVERGENCE AMONG THE MODELS AND HOW THEY HANDLE THE CURRENT SHORTWAVE TROUGH/LOW OVER THE SOUTHEASTERN U.S. WATER VAPOR IMAGERY INDICATES THE TROUGH HAS BECOME NEGATIVELY TILTED IN AN EAST-WEST ORIENTATION. THIS WOULD SUGGEST THAT THE LOW SHOULD BEGIN TO LIFT OUT AND ALLOW THE RIDGE NORTH OF ISABEL TO GRADUALLY BUILD WESTWARD...WHICH IS SIMILAR TO THE 06Z GFS...GFDL...AND ETA...AND 00Z UKMET SOLUTIONS. THE KEY WILL BE HOW THE CENTRAL U.S. TROUGH EVOLVES AND HOW DEEP IT DIGS INTO THE SOUTHERN U.S. AND GULF OF MEXICO. THE OFFICIAL FORECAST WAS ADJUSTED SLIGHTLY TO THE LEFT OF AND SLOWER THAN THE PREVIOUS FORECAST...WHICH IS CONSISTENT WITH THE GUNA MODEL CONSENSUS. HOWEVER...IT IS STILL TOO EARLY TO DETERMINE WHEN OR WHERE ISABEL WILL MAKE LANDFALL. HOPEFULLY...THE NOAA GULFSTREAM-IV SYNOPTIC DATA MISSION AT 14/00Z WILL PROVIDE BETTER MODEL CONVERGENCE. ALTHOUGH ISABEL HAS A RATHER LARGE EYE DIAMETER...CONDITIONS APPEAR FAVORABLE FOR AT LEAST SOME SLIGHT ADDITIONAL STRENGTHENING OVER THE NEXT COUPLE OF DAYS AS THE HURRICANE MOVES OVER WARMER WATER. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 13/1500Z 22.2N 61.5W 130 KT 12HR VT 14/0000Z 22.6N 63.0W 135 KT 24HR VT 14/1200Z 23.0N 64.8W 135 KT 36HR VT 15/0000Z 23.7N 66.7W 130 KT 48HR VT 15/1200Z 24.5N 68.7W 130 KT 72HR VT 16/1200Z 26.0N 71.0W 125 KT 96HR VT 17/1200Z 28.5N 73.0W 120 KT 120HR VT 18/1200Z 31.5N 75.0W 110 KT NNNN
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Page last modified: Monday, 07-Feb-2005 16:49:58 UTC