[Tropical] Tropical Cyclone Discussion

[Nashville EMWIN]

WTNT41 KNHC 040259
TCDAT1
HURRICANE FRANCES DISCUSSION NUMBER  41
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT FRI SEP 03 2004

RADAR...SATELLITE...RECON DATA...AND NUMEROUS SURFACE REPORTS FROM
HAM RADIO OPERATORS...SURFACE STATIONS...AND SHIPS IN AND AROUND
THE CENTRAL AND NORTHWESTERN BAHAMAS...AND THE FLORIDA EAST COAST
INDICATE THAT FRANCES HAS WEAKENED SINCE THE 18Z ADVISORY. HOWEVER
...THE SURFACE PRESSURE IN THE EYE HAS NOT CHANGED FROM 959-960 MB
SINCE ABOUT 22Z. BRIEF BURSTS OF DEEP CONVECTION HAVE BEEN
DEVELOPING IN THE NORTHERN SEMICIRCLE WHICH HAVE BEEN HELPING TO
MAINTAIN A 90-KT INTENSITY.

THE INITIAL MOTION HAS SLOWED TO 295/05. DROPSONDE DATA AND 18Z
UPPER-AIR DATA INDICATE THE WRAPAROUND MID-LEVEL RIDGE TO THE NORTH
OF FRANCES HAS NOT MOVED...WITH A HIGH CENTER LOCATED OVER
SOUTHEAST GEORGIA AND RIDGES EXTENDING EASTWARD AND SOUTHWESTWARD
FROM THE HIGH FOR SEVERAL HUNDRED MILES. THIS HAS TRAPPED FRANCES
IN A WEAK STEERING REGIME...WHICH IS EXPECTED TO LAST FOR AT LEAST
THE NEXT 36 HOURS. AFTER THAT...THE RIDGE OVER THE EASTERN GULF OF
MEXICO IS FORECAST BY ALL OF THE MODELS TO ERODE SLOWLY EASTWARD
AND ALLOW FRANCES TO TURN NORTHWESTWARD AND THEN NORTHWARD BY 72
HOURS. IT IS INTERESTING TO POINT OUT THAT THE GFDL AND GFS MODELS
THAT PREVIOUSLY FOR SEVERAL DAYS HAD BEEN THE RIGHTMOST OF THE NHC
MODEL SUITE ARE NOW THE LEFTMOST MODELS...AND TAKE FRANCES ACROSS
THE NORTHERN PORTION OF LAKE OKEECHOBEE IN ABOUT 36 HOURS. THE
OFFICIAL TRACK IS SLIGHTLY LEFT OF THE PREVIOUS TRACK AND TO THE
LEFT OF THE GUNA CONSENSUS MODEL.

SOME WESTERLY WINDS BETWEEN 300-250 MB HAVE BEEN UNDERCUTTING THE
IMPRESSIVE UPPER-LEVEL OUTFLOW LAYER. THIS UNFAVORABLE SHEAR
PATTERN...COMBINED WITH MID-LEVEL DRY AIR ENTRAINMENT...HAS LIKELY
LED TO THE WEAKENING OVER THE PAST 24 HOURS. THE GFS-ETA-GFDL
MODELS FORECAST THE SHEAR PATTERN TO WEAKEN OR DISAPPEAR IN 18-24
HOURS...AT ABOUT THE TIME FRANCES IS SLOWLY CROSSING THE WARMER
GULFSTREAM. HOWEVER...GIVEN THE ALREADY EXPANDED AND LARGE INNER
CORE WIND FIELD...ONLY SLIGHT INTENSIFICATION IS EXPECTED. THIS
SCENARIO IS SIMILAR TO THE GFDL INTENSITY FORECAST.

BECAUSE FRANCES IS A SLOW MOVING HURRICANE...IT COULD BRING
TORRENTIAL RAINS TO PORTIONS OF FLORIDA SATURDAY NIGHT AND SUNDAY.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL      04/0300Z 26.1N  77.8W    90 KT
 12HR VT     04/1200Z 26.5N  78.6W    90 KT
 24HR VT     05/0000Z 27.0N  79.8W    95 KT
 36HR VT     05/1200Z 27.6N  81.2W    55 KT...INLAND
 48HR VT     06/0000Z 28.7N  83.1W    35 KT...OVER GULF OF MEXICO
 72HR VT     07/0000Z 31.9N  86.2W    30 KT...INLAND
 96HR VT     08/0000Z 35.0N  87.0W    25 KT...INLAND
120HR VT     09/0000Z 40.0N  84.5W    20 KT...INLAND


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