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TROPICAL STORM ISELLE DISCUSSION NUMBER   8
NATIONAL WEATHER SERVICE MIAMI FL
2 PM PDT MON SEP 16 2002
 
ALTHOUGH DVORAK CLASSIFICATIONS ARE NOW T3.5...55 KT...A QUIKSCAT
PASS THIS MORNING SUGGESTS THAT THE WINDS ARE NOT THAT HIGH.  THE
PASS SHOWED NOTHING HIGHER THAN 40 KT...AND SO THE CURRENT INTENSITY
IS HELD AT 45 KT.  AS FEARED EARLIER...VISIBLE IMAGERY CONFIRMS THAT
ISELLE WAS FARTHER NORTH THAN THE PREVIOUS ADVISORY GAVE IT CREDIT
FOR.  THE INITIAL MOTION IS STILL NOT VERY CERTAIN...BUT ESTIMATED
TO BE 300/14.
 
THERE HAS BEEN A SHIFT IN MUCH OF THE MODEL GUIDANCE...WITH THE AVN
AND UKMET NOW RECURVING ISELLE INTO BAJA CALIFORNIA THROUGH A BREAK
IN THE SUBTROPICAL RIDGE.  OUR CURRENT TRACK FORECAST IS TO THE 
RIGHT OF THE PREVIOUS ADVISORY...HOWEVER WE ARE STILL TO THE LEFT OF 
THE AVN/UKMET/GFDL CLUSTER.  THERE DOES NOT APPEAR TO BE ANY OBVIOUS 
REASON FOR THE GUIDANCE SHIFT...AS THE ENVIRONMENTAL FIELDS LOOK 
FAIRLY SIMILAR...AT LEAST IN THE LAST TWO AVN RUNS.  AS A 
RESULT...WE ARE NOT BITING COMPLETELY ON THIS SHIFT JUST YET.  

LITTLE CHANGE HAS BEEN MADE TO THE PREVIOUS INTENSITY FORECAST... 
WHICH IS SLIGHTLY ABOVE THE SHIPS GUIDANCE.  WHILE CURRENTLY UNDER 
EASTERLY SHEAR...THIS IS FORECAST TO RELAX AS THE STORM MOVES 
UNDERNEATH AN UPPER-LEVEL RIDGE THAT LIES ALONG 22 NORTH.  THE 
RECURVATURE LONGITUDE WILL ALSO BE KEY IN DETERMINING THE SSTS UNDER 
THE CYCLONE.  ON THE CURRENT FORECAST TRACK...ISELLE WILL BE PASSING 
THE 26C ISOTHERM IN ABOUT 36 HOURS.  A SHARPER RECURVATURE WOULD 
KEEP THE CYCLONE OVER WARMER WATER LONGER. 

FORECASTER FRANKLIN/MAINELLI
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     16/2100Z 19.8N 111.0W    45 KTS
12HR VT     17/0600Z 20.6N 112.5W    50 KTS
24HR VT     17/1800Z 21.6N 114.0W    55 KTS
36HR VT     18/0600Z 22.5N 115.1W    65 KTS
48HR VT     18/1800Z 23.5N 116.0W    60 KTS
72HR VT     19/1800Z 25.0N 117.0W    50 KTS
 
 
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