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| #6206 (Received by flhurricane at: 10:48 AM 27.Aug.2004) TCDAT1 HURRICANE FRANCES DISCUSSION NUMBER 11 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 AM EDT FRI AUG 27 2004 FRANCES CONTINUES TO BECOME BETTER ORGANIZED WHILE STRENGTHENING TO 90 KT. THE INITIAL INTENSITY IS SUPPORTED BY A DVORAK SATELLITE INTENSITY ESTIMATE OF T5.0...OR 90 KT...FROM TAFB...A SATELLITE DATA T-NUMBER OF 5.0 FORM AFWA...AND 27/1010Z UW-CIMSS AMSU PRESSURE RETRIEVAL OF 969.8 MB...WHICH EQUATES TO ABOUT 90 KT. THE OUTFLOW REMAINS EXCELLENT AND ALSO CONTINUES TO IMPROVE. THE MOTION IS NOW 300/09. FRANCES REMAINS ON TRACK AND HAS BEGUN TO SLOW DOWN. A NORTHWESTWARD JOG MAY OCCUR...BUT IT IS EXPECTED TO BE SHORT-LIVED AS THE WEAKNESS IN THE SUBTROPICAL RIDGE TO THE NORTH OF FRANCES IS FORECAST TO QUICKLY FILL IN AS THE SHORTWAVE TROUGH NOTED IN WATER VAPOR IMAGERY ALONG 52W LONGITUDE CONTINUES TO ZIP ALONG EASTWARD. THE NHC MODEL GUIDANCE IS IN STRONG AGREEMENT ON A WEST-NORTHWEST TO NORTHWESTWARD TRACK THROUGH 48 HOURS...BUT THEN DIVERGE SIGNIFICANTLY AFTER THAT. HOWEVER...DESPITE THE DIFFERING TRACKS...ALL OF THE MODELS AGREE ON HIGH ZONAL FLOW WITH STRONG WESTERLIES DEVELOPING ACROSS THE NORTHERN U.S. AND THE NORTH ATLANTIC AFTER 48HR. SUCH A STRONG HIGH-LATITUDE ZONAL FLOW PATTERN IS USUALLY REFLECTED BY A STRONG SUBTROPICAL RIDGE TO THE SOUTH THAT EXTENDS EAST-WEST FROM THE AZORES TO BERMUDA AND INTO THE SOUTHEASTERN U.S. MY CONCERN IS THAT THE RIDGE MAY BUILD IN FASTER THAN EXPECTED AND DRIVE FRANCES MORE WESTWARD SOONER THAN FORECAST ...WHICH IS WHAT THE 06Z GFS MODEL IS INDICATING. HOWEVER...MAKING SUCH A SUDDEN AND SHARP 45 DEGREE LEFT-OF-TRACK TURN AT 48 HOURS IS PROBABLY OVERDOING IT SOME...BUT OUT OF RESPECT FOR THE CONSISTENT TREND IN THE GFS MODEL THE PAST 24 HOURS...THE FORECAST TRACK HAS BEEN NUDGED A LITTLE MORE SOUTH AND WESTWARD IN 72-120HR. FRANCES IS EXPECTED TO REMAIN IN A LOW SHEAR ENVIRONMENT AND OVER INCREASING SSTS THROUGHOUT THE PERIOD...SO AT LEAST SOME SLOW INTENSIFICATION SHOULD OCCUR. THE SHIPS MODEL SHARPLY BRINGS DOWN THE INTENSITY TO 73 KT AFTER 72 HOURS DUE TO INCREASING WESTERLY SHEAR OF 25-30 KT. HOWEVER...THE VERTICAL SHEAR IS FICTITIOUS AND 'SELF-INFLICTED' BY THE GFS/SHIPS MODEL...DUE TO THE OFFICIAL FORECAST TRACK BEING ABOUT 180 NMI NORTH OF THE GFS FORECAST POSITIONS IN 72-120H. THIS PUTS FRANCES IN THE STRONG WESTERLY FLOW IN THE NORTHERN SEMICIRCLE OF A VERY INTENSE UPPER-LEVEL HIGH THAT ALL THE MODELS DEVELOP OVER FRANCES. THE SHIPS MODEL WAS DISCOUNTED AND THE OFFICIAL INTENSITY FORECAST LEANS TOWARD THE GFDL SOLUTION. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 27/1500Z 15.0N 49.0W 90 KT 12HR VT 28/0000Z 15.8N 50.4W 100 KT 24HR VT 28/1200Z 17.0N 52.1W 100 KT 36HR VT 29/0000Z 18.0N 53.6W 105 KT 48HR VT 29/1200Z 18.9N 55.2W 105 KT 72HR VT 30/1200Z 20.2N 58.5W 110 KT 96HR VT 31/1200Z 21.0N 62.0W 110 KT 120HR VT 01/1200Z 22.0N 67.0W 110 KT |
