Tropical Storm FRANCES

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TROPICAL STORM FRANCES DISCUSSION NUMBER   7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT THU AUG 26 2004
 
FRANCES HAS BECOME MUCH BETTER ORGANIZED DURING THE PAST 12 HOURS...
AS NOTED BY THE TIGHT COILING OF BOTH THE INNER AND OUTER
CONVECTIVE BANDS...AND AN OCCASIONAL HINT OF A BANDING EYE FEATURE.
A DVORAK SATELLITE INTENSITY ESTIMATE OF T3.5 WAS OBTAINED FROM
BOTH TAFB AND SAB. HOWEVER...BANDING FEATURES AND INNER-CORE
CONVECTION HAVE IMPROVED SINCE THE 12Z FIXES...SO I HAVE CONTINUED
THE TREND FROM THE PREVIOUS ADVISORY OF GOING SLIGHTLY HIGHER THAN
THE SATELLITE ESTIMATES ARE INDICATING. UPPER-LEVEL OUTFLOW IS GOOD
IN ALL QUADRANTS AND IS BECOMING MORE CIRCULAR.
 
THE INITIAL MOTION REMAINS 290/15. FRANCES HAS BASICALLY REMAINED ON
TRACK THE PAST 24 HOURS. HOWEVER...THE NHC MODEL GUIDANCE IS NOT IN
GOOD AGREEMENT AFTER 36 HOURS. THE NOGAPS...UKMET...AND ECMWF TAKE
FRANCES MORE NORTHWESTWARD THOUGHOUT THE FORECAST PERIOD...WHEREAS
THE GFDL...GFS...AND THE CANADIAN MODELS TAKE THE CYCLONE MORE
WEST-NORTHWESTWARD AND EVEN WESTWARD. THE MAIN DIFFERENCES LIE IN
HOW MUCH EROSION OF THE SUBTROPICAL RIDGE OCCURS NORTH OF FRANCES
IN 36-72 HOURS AS A LARGE EXTRATROPICAL LOW OFF THE CANADIAN
MARITIMES DIGS SOUTHWARD. THE UKMET AND NOGAPS MODEL SHOW MORE
EROSION OF THE RIDGE...WHILE THE GFS...GFDL...AND CANADIAN MODELS
LIFT OUT THE UPPER-LOW MORE QUICKLY...WHICH ALLOWS THE RIDGE TO
BUILD BACK WESTWARD TO THE NORTH OF THE CYCLONE AFTER 72 HOURS. THE
PAST 24 HOUR TREND IN WATER VAPOR IMAGERY SUGGESTS THAT THE
UPPER-LOW HAS PROBABLY PUSHED ABOUT AS FAR SOUTH AS IT CAN...WHICH
WOULD SUPPORT THE GFS-GFDL-CANADIAN SCENARIO OF A MORE WESTWARD
TRACK BY 96 HOURS. THE PAST 4 GFDL RUNS HAVE SUCCESSIVELY SHIFTED
THE TRACK MORE WESTWARD WITH EACH RUN...WHILE THE GFS HAS A LEFT OF
TRACK BIAS. THEREFORE...THE OFFICIAL TRACK WAS SHIFTED SLIGHTLY
LEFT OF THE PREVIOUS FORECAST AND LEFT OF THE LATEST GFDL RUN...BUT
NOT AS FAR WEST OR AS FAST AS THE GFS AND CANADIAN MODELS.

FRANCES MAY BE ON A FAST-TRACK IN ITS DEVELOPMENT PROCESS...BUT I
WOULD PREFER TO WAIT AND SEE IF ANY DRY AIR ON THE EAST SIDE GETS
WRAPPED INTO THE CENTER.  HOWEVER...IF A DISTINCT EYE APPEARS LATER
TODAY...THEN RAPID INTENSIFICATION...AND ALSO MAKING FRANCES A
MAJOR HURRICANE IN 48-72 HOURS LIKE THE GFDL AND SHIPS MODELS ARE
INDICATING...WILL HAVE TO BE CONSIDERED ON THE NEXT ADVISORY.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/1500Z 13.1N  45.0W    60 KT
 12HR VT     27/0000Z 14.0N  47.0W    70 KT
 24HR VT     27/1200Z 15.2N  49.2W    80 KT
 36HR VT     28/0000Z 16.4N  51.1W    90 KT
 48HR VT     28/1200Z 17.5N  52.3W    95 KT
 72HR VT     29/1200Z 18.6N  54.0W    95 KT
 96HR VT     30/1200Z 20.0N  57.0W    95 KT
120HR VT     31/1200Z 21.0N  61.0W    95 KT
 
 
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