Tropical Storm IVAN

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TROPICAL STORM IVAN DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT FRI SEP 03 2004
 
SATELLITE DVORAK INTENSITY ESTIMATES REMAIN AT 45 KT FROM TAFB AND
SAB.  A RECENT QUIKSCAT PASS HAD RAIN-FLAGGED 55 KT SURFACE WINDS
WELL SOUTH OF THE CENTER AND SO DID A PASS FROM EARLY FRIDAY
MORNING.  SINCE THE DVORAK ESTIMATES HAVE BEEN THE SAME ALL DAY
FROM SAB...THE OFFICIAL INTENSITY WILL STAY THE SAME AS THE
PREVIOUS ADVISORY...45 KT.
 
THE SHIPS MODEL BRINGS THE WIND SPEED TO 96 KT IN 120 HOURS UNDER
DECREASING VERTICAL WIND SHEAR AND OF COURSE WARM SSTS OVER THE
TROPICAL ATLANTIC.  THE GFDL IS MUCH MORE AGGRESSIVE BUT...AS IS
USUALLY THE CASE...THE OFFICIAL FORECAST FOLLOWS THE SHIPS MODEL
AND IS SIMILAR TO THE PREVIOUS ADVISORY.
 
THE INITIAL POSITION IS A LITTLE NORTH OF THE GOES 12 INFRARED FIXES
BASED ON AN ANALYSIS OF THE 2228Z QUIKSCAT AMBIGUITY WIND FIELD.
THIS GIVES AN INITIAL MOTION ESTIMATE OF 265/15.  THE GLOBAL MODELS
ALL SHOW THE SUBTROPICAL RIDGE HOLDING TO THE NORTH OF IVAN AND ALL
SHOW A WEST-NORTHWEST TRACK EXCEPT BECOMING A LITTLE MORE
NORTHWESTWARD AFTER 96 HOURS.  THE GFS IS THE LEFT-MOST TRACK AND
THE NOGAPS AND GFDL EMBEDDED IN THE NOGAPS ARE THE RIGHT-MOST
TRACKS.  THE OFFICIAL TRACK FORECAST IS ADJUSTED TO THE RIGHT OF
THE PREVIOUS FORECAST BUT IS STILL LEFT OF A CONSENSUS OF THE
GLOBAL MODELS.  IN ANY CASE IVAN SHOULD MOVE SOMEWHERE ACROSS THE
LESSER ANTILLES IN 4 TO 5 DAYS.
 
 
FORECASTER LAWRENCE
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      04/0300Z  9.1N  35.8W    45 KT
 12HR VT     04/1200Z  9.2N  38.0W    55 KT
 24HR VT     05/0000Z  9.4N  41.0W    60 KT
 36HR VT     05/1200Z 10.2N  44.0W    65 KT
 48HR VT     06/0000Z 11.0N  47.0W    75 KT
 72HR VT     07/0000Z 12.5N  53.5W    85 KT
 96HR VT     08/0000Z 14.5N  59.5W    90 KT
120HR VT     09/0000Z 16.5N  64.0W    95 KT
 
 
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