Hurricane FRANCES

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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
 
 
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