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| #6351 (Received by flhurricane at: 4:49 PM 28.Aug.2004) TCDAT1 HURRICANE FRANCES DISCUSSION NUMBER 16 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 PM EDT SAT AUG 28 2004 FRANCES HAS CONTINUED TO STRENGTHEN WHILE MAINTAINING A 20 NMI DIAMETER EYE. THE INITIAL INTENSITY IS SET AT 115 KT BASED ON A DVORAK INTENSITY ESTIMATE OF T6.0...OR 115 KT...FROM BOTH TAFB AND SAB...A 3-HR AVERAGE ODT OF T5.9...OR 113 KT...A 2.5-HR AVERAGE ODT OF T6.0...AND A SUBSEQUENT INCREASE IN THE DVORAK DATA T-NUMBER TO T6.5...OR 127 KT...SINCE THE 18Z SATELLITE ESTIMATES WERE MADE. BASED ON THIS INFORMATION...FRANCES IS NOW A CATEGORY 4 HURRICANE ON THE SAFFIR-SIMPSON HURRICANE SCALE. THE INITIAL MOTION IS 305/08. FRANCES REMAINS ON TRACK AND APPEARS TO BE MAKING A TURN BACK TOWARD THE WEST-NORTHWEST. OTHERWISE... THERE IS NO CHANGE TO THE PREVIOUS TRACK FORECASTS OR REASONINGS. MOST OF THE NHC MODEL GUIDANCE AGREES ON GRADUALLY BUILDING THE SUBTROPICAL RIDGE WESTWARD TO THE NORTH OF FRANCES THROUGHOUT THE FORECAST PERIOD. THE NHC RUNNING TRACK ERRORS THROUGH 28/18Z ARE 44...71...AND 104 NMI AT 24-...48-...AND 72-HR...RESPECTIVELY. THESE ERRORS ARE HALF OUR AVERAGE ERRORS...AND ARE BETTER THAN ALL OF THE COMPUTER MODELS...INCLUDING THE CONSENSUS MODELS. THEREFORE ...WE HAVE A FAIR DEGREE OF CONFIDENCE IN OUR FORECAST TRACK...WHICH REMAINS BETWEEN THE GFS MODEL TO THE SOUTH AND THE UKMET MODEL TO THE NORTH. THE NOGAPS MODEL HAS BEEN BY FAR THE WORSE PERFORMING MODEL WITH ITS STRONG RIGHT OF TRACK BIAS...SO IT WAS IGNORED FOR THIS PACKAGE. WHILE OUR CURRENT FORECAST ERRORS ARE QUITE GOOD... THERE IS STILL ENOUGH UNCERTAINTY IN THE LONGER TIME PERIODS TO MAKE IT TOO EARLY TO TRY AND DETERMINE IF...WHEN...AND WHERE FRANCES WILL MAKE LANDFALL. HOWEVER...NOW WOULD BE A GOOD TIME FOR EVERYONE IN THE SOUTHEASTERN U.S...THE BAHAMAS...AND THE TURKS AND CAICOS ISLANDS TO CHECK THEIR HURRICANE PREPAREDNESS PLANS AND SUPPLIES. FRANCES IS EMBEDDED IN A LOW-SHEAR ENVIRONMENT WITH EXCELLENT OUTFLOW IN ALL QUADRANTS...INCLUDING AN OUTFLOW CHANNEL TO THE NORTH. THE SSTS BETWEEN 62-68W LONGITUDE ARE NEAR 29C...SO AT LEAST SOME ADDITIONAL SLOW INTENSIFICATION SHOULD OCCUR. IT IS POSSIBLE THAT FRANCES COULD EVEN REACH NEAR-CATEGORY 5 INTENSITY AT ANY TIME DURING THE FORECAST PERIOD...BUT A BETTER OPPORTUNITY WOULD BE AFTER 84 HOURS WHEN THE HURRICANE WILL BE MOVING OVER NEAR-30C SSTS WHEN A 50-60 KT NORTHERLY WIND SPEED MAXIMUM IS FORECAST BY THE GFS ...UKMET...GFDL...AND NOGAPS MODELS TO DIG SOUTHWARD ALONG THE EAST SIDE OF FRANCES...ENHANCING THE OUTFLOW IN THE EASTERN SEMICIRCLE. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 28/2100Z 17.9N 52.6W 115 KT 12HR VT 29/0600Z 18.7N 53.9W 120 KT 24HR VT 29/1800Z 19.4N 55.8W 125 KT 36HR VT 30/0600Z 20.0N 58.0W 125 KT 48HR VT 30/1800Z 20.5N 60.5W 125 KT 72HR VT 31/1800Z 21.3N 65.4W 125 KT 96HR VT 01/1800Z 22.5N 70.5W 125 KT 120HR VT 02/1800Z 24.0N 75.5W 125 KT |
