Hurricane ISABEL

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HURRICANE ISABEL DISCUSSION NUMBER  19
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT WED SEP 10 2003
 
SATELLITE IMAGERY INDICATES ISABEL HAS STRENGTHENED THIS AFTERNOON
AS EYEWALL CLOUD TOPS HAVE COOLED TO -75C AND COLDER...WHILE THE EYE
HAS CLEARED OUT AND WARMED SIGNIFICANTLY. OBJECTIVE DVORAK
T-NUMBERS OVER THE PAST 2 HOURS AVERAGE OUT TO T6.5...OR 127 KT...
WITH A PEAK T-NUMBER OF 7.1...OR 143 KT...AT 1815Z. THE 3-HOUR ODT
AVERAGE IS T6.3...OR 122 KT. THESE INTENSITY ESTIMATES EASILY
JUSTIFY INCREASING THE INTENSITY TO 120 KT FOR THIS ADVISORY. IT IS
QUITE POSSIBLE THAT ISABEL IS A LITTLE STRONGER THAN THE ADVISORY
INTENSITY INDICATES...BUT WE PREFER TO USE THE 3-HOUR ODT VALUES TO
SMOOTH OUT ANY INTENSITY FLUCTUATIONS.
 
THE INITIAL MOTION ESTIMATE IS 275/10. THERE REMAINS NO SIGNIFICANT
CHANGE TO THE PREVIOUS FORECAST TRACKS OR REASONINGS. ISABEL HAS
DEFINITELY MADE THE TURN TOWARD THE WEST. UNFORTUNATELY...THE 12Z
GFS MODEL HAS RETURNED TO ITS OLD WAYS AND NOW MAKES A JOG BACK TO
THE WEST-SOUTHWEST ALONG 20N LATITUDE IN 36-48 HOURS. THIS APPEARS
TO BE DUE TO POOR INITIALIZATION OF ISABEL BY THE MODEL...AND THE
GFS MAINTAINS A PATHETIC LOOKING LOW- TO MID-LEVEL CIRCULATION...
CERTAINLY NOTHING REMOTELY RESEMBLING A MAJOR HURRICANE...THROUGH
72 HOURS. THE RESULT IS THAT WEAK MID-LEVEL RIDGING TO THE WEST OF
ISABEL FORCES THE CYCLONE WEST-SOUTHWESTWARD. THE CANADIAN MODEL
AND THE UKMET... TO A SLIGHTLY LESSER DEGREE...ALSO HAVE SIMILAR
LOOKING WEAK CIRCULATIONS...THROUGH THE SAME TIME PERIOD. ONLY THE
12Z NOGAPS MODEL INITIALIZES ISABEL AS A SIGNIFICANT TROPICAL
CYCLONE. SINCE THE NOGAPS MODEL IS VERY CLOSE TO THE PREVIOUS
FORECAST TRACK...LITTLE CHANGE WAS MADE TO THE PREVIOUS TRACK
....WHICH IS A LITTLE SOUTH OF THE NHC MODEL CONSENSUS AND CLOSE TO
THE NOGAPS AND GFDL SOLUTIONS.
 
THE OUTFLOW ON THE WEST SIDE OF ISABEL CONTINUES TO EXPAND WESTWARD
AS IS GETS DRAWN INTO THE LARGE MID-/UPPER-LOW NORTH OF HISPANIOLA.
THE CYCLONE WILL CONTINUE TO MOVE OVER WARMER WATER AND REMAIN IN A
FAVORABLE UPPER-LEVEL OUTFLOW PATTERN...SO SOME ADDITIONAL SLIGHT
STRENGTHENING IS STILL POSSIBLE AT ANY TIME. HOWEVER...THE ONLY GOOD
NEWS ABOUT INTENSE HURRICANES IS THAT THEY GENERALLY DO NOT REMAIN
INTENSE FOR VERY LONG...SO SOME SLIGHT WEAKENING IS FORECAST.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      10/2100Z 21.2N  51.9W   120 KT
 12HR VT     11/0600Z 21.3N  53.5W   125 KT
 24HR VT     11/1800Z 21.4N  55.2W   120 KT
 36HR VT     12/0600Z 21.5N  56.9W   120 KT
 48HR VT     12/1800Z 21.7N  58.6W   120 KT
 72HR VT     13/1800Z 22.0N  62.5W   115 KT
 96HR VT     14/1800Z 23.0N  66.0W   115 KT
120HR VT     15/1800Z 23.5N  69.5W   115 KT
 
 
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