Tropical Storm FRANCES

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TROPICAL STORM FRANCES DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT WED AUG 25 2004
 
AFTER LOOKING RAGGED THIS MORNING...THE CONVECTION ASSOCIATED WITH
TROPICAL DEPRESSION SIX HAS BECOME BETTER ORGANIZED THIS AFTERNOON
WITH A SMALL CENTRAL DENSE OVERCAST AND A BAND WRAPPED AROUND THE
WESTERN SEMICIRCLE.  SATELLITE INTENSITY ESTIMATES ARE 35 KT FROM
TAFB AND SAB...SO THE DEPRESSION IS UPGRADED TO TROPICAL STORM
FRANCES WITH 35 KT WINDS.
 
THE INITIAL MOTION IS 275/15.  THE CYCLONE REMAINS SOUTH OF A
SUBTROPICAL RIDGE.  LARGE-SCALE MODELS INDICATE THAT A MID/
UPPER-LEVEL LEVEL LOW CURRENTLY SEEN IN WATER VAPOR IMAGERY SOUTH OF
NEWFOUNDLAND WILL DIVE SOUTHEASTWARD AND WEAKEN THE RIDGE FROM
48-96 HR...AND THEN LIFT OUT TO THE NORTHEAST.  IF THIS VERIFIES...
IT WOULD ALLOW FRANCES TO TURN NORTHWESTWARD AFTER 24 HR...AND THEN
POSSIBLY TURNING MORE WESTWARD BY 120 HR AS THE RIDGE REBUILDS TO
THE NORTH.  THE DYNAMICAL MODELS GENERALLY AGREE WITH THIS
SCENARIO.  HOWEVER...THE GFS TRACK REMAINS TO THE SOUTH AND WEST OF
THE GFDL...UKMET...AND NOGAPS.  THE OFFICIAL FORECAST TRACK FOLLOWS
THIS SCENARIO AND IS SHIFTED JUST A LITTLE WEST OF THE PREVIOUS
PACKAGE...IN BEST AGREEMENT WITH THE GFDL AND WEST OF ALL THE
DYNAMICAL MODELS EXCEPT THE GFS.
 
CONDITIONS GENERALLY APPEAR FAVORABLE FOR STRENGTHENING FOR THE
FIRST 72-96 HR...WITH THE ONLY SEEMING NEGATIVE FACTOR BEING THE
DRY AIR SURROUNDING FRANCES IN WATER VAPOR IMAGERY. THE INTENSITY
FORECAST WILL CALL FOR SLOW STRENGTHENING FOR THE FIRST 36 HR OR SO
IN AGREEMENT WITH THE CURRENT ORGANIZATION AND TRENDS...THEN CALL
FOR FASTER DEVELOPMENT AS THE SYSTEM NEARS HURRICANE STRENGTH.
AFTER 72-96 HR...IF THE CYCLONE TRACKS AS FAR NORTH AS
FORECAST...IT MAY ENCOUNTER WESTERLY SHEAR TO THE NORTH OF THE
UPPER-LEVEL RIDGE FORECAST TO LIE EAST- WEST ALONG 18-19N. THAT
WOULD LIMIT STRENGTHENING AS INDICATED IN THE FORECAST. A
CONTINUING ALTERNATE SCENARIO WOULD BE IF THE CYCLONE STAYS SOUTH
OF THE RIDGE AXIS...WHICH WOULD ALLOW GREATER STRENGTHENING THAN
CURRENTLY FORECAST.


FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      25/2100Z 11.6N  40.5W    35 KT
 12HR VT     26/0600Z 12.0N  42.7W    40 KT
 24HR VT     26/1800Z 13.0N  45.0W    45 KT
 36HR VT     27/0600Z 13.9N  46.6W    50 KT
 48HR VT     27/1800Z 14.9N  48.1W    60 KT
 72HR VT     28/1800Z 17.0N  50.5W    70 KT
 96HR VT     29/1800Z 18.5N  52.5W    80 KT
120HR VT     30/1800Z 20.5N  55.5W    80 KT
 
 
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