ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM HURRICANE ISABEL DISCUSSION NUMBER 19 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 PM EDT WED SEP 10 2003 SATELLITE IMAGERY INDICATES ISABEL HAS STRENGTHENED THIS AFTERNOON AS EYEWALL CLOUD TOPS HAVE COOLED TO -75C AND COLDER...WHILE THE EYE HAS CLEARED OUT AND WARMED SIGNIFICANTLY. OBJECTIVE DVORAK T-NUMBERS OVER THE PAST 2 HOURS AVERAGE OUT TO T6.5...OR 127 KT... WITH A PEAK T-NUMBER OF 7.1...OR 143 KT...AT 1815Z. THE 3-HOUR ODT AVERAGE IS T6.3...OR 122 KT. THESE INTENSITY ESTIMATES EASILY JUSTIFY INCREASING THE INTENSITY TO 120 KT FOR THIS ADVISORY. IT IS QUITE POSSIBLE THAT ISABEL IS A LITTLE STRONGER THAN THE ADVISORY INTENSITY INDICATES...BUT WE PREFER TO USE THE 3-HOUR ODT VALUES TO SMOOTH OUT ANY INTENSITY FLUCTUATIONS. THE INITIAL MOTION ESTIMATE IS 275/10. THERE REMAINS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACKS OR REASONINGS. ISABEL HAS DEFINITELY MADE THE TURN TOWARD THE WEST. UNFORTUNATELY...THE 12Z GFS MODEL HAS RETURNED TO ITS OLD WAYS AND NOW MAKES A JOG BACK TO THE WEST-SOUTHWEST ALONG 20N LATITUDE IN 36-48 HOURS. THIS APPEARS TO BE DUE TO POOR INITIALIZATION OF ISABEL BY THE MODEL...AND THE GFS MAINTAINS A PATHETIC LOOKING LOW- TO MID-LEVEL CIRCULATION... CERTAINLY NOTHING REMOTELY RESEMBLING A MAJOR HURRICANE...THROUGH 72 HOURS. THE RESULT IS THAT WEAK MID-LEVEL RIDGING TO THE WEST OF ISABEL FORCES THE CYCLONE WEST-SOUTHWESTWARD. THE CANADIAN MODEL AND THE UKMET... TO A SLIGHTLY LESSER DEGREE...ALSO HAVE SIMILAR LOOKING WEAK CIRCULATIONS...THROUGH THE SAME TIME PERIOD. ONLY THE 12Z NOGAPS MODEL INITIALIZES ISABEL AS A SIGNIFICANT TROPICAL CYCLONE. SINCE THE NOGAPS MODEL IS VERY CLOSE TO THE PREVIOUS FORECAST TRACK...LITTLE CHANGE WAS MADE TO THE PREVIOUS TRACK ....WHICH IS A LITTLE SOUTH OF THE NHC MODEL CONSENSUS AND CLOSE TO THE NOGAPS AND GFDL SOLUTIONS. THE OUTFLOW ON THE WEST SIDE OF ISABEL CONTINUES TO EXPAND WESTWARD AS IS GETS DRAWN INTO THE LARGE MID-/UPPER-LOW NORTH OF HISPANIOLA. THE CYCLONE WILL CONTINUE TO MOVE OVER WARMER WATER AND REMAIN IN A FAVORABLE UPPER-LEVEL OUTFLOW PATTERN...SO SOME ADDITIONAL SLIGHT STRENGTHENING IS STILL POSSIBLE AT ANY TIME. HOWEVER...THE ONLY GOOD NEWS ABOUT INTENSE HURRICANES IS THAT THEY GENERALLY DO NOT REMAIN INTENSE FOR VERY LONG...SO SOME SLIGHT WEAKENING IS FORECAST. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 10/2100Z 21.2N 51.9W 120 KT 12HR VT 11/0600Z 21.3N 53.5W 125 KT 24HR VT 11/1800Z 21.4N 55.2W 120 KT 36HR VT 12/0600Z 21.5N 56.9W 120 KT 48HR VT 12/1800Z 21.7N 58.6W 120 KT 72HR VT 13/1800Z 22.0N 62.5W 115 KT 96HR VT 14/1800Z 23.0N 66.0W 115 KT 120HR VT 15/1800Z 23.5N 69.5W 115 KT NNNN
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Page last modified: Monday, 07-Feb-2005 16:49:58 UTC