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TROPICAL STORM ISELLE DISCUSSION NUMBER   9
NATIONAL WEATHER SERVICE MIAMI FL
8 PM PDT MON SEP 16 2002
 
THE LAST FEW VISIBLE IMAGES SHOWED A TIGHT CIRCULATION WITH AN
IMPRESSIVE BAND WRAPPING AROUND THE SOUTH AND WEST REGIONS OF THE
STORM.  IN ADDITION...RECENT INFRARED PICTURES INDICATE A LARGE
BURST OF CONVECTION NEAR THE CENTER.  DVORAK ESTIMATES SUGGEST AN
INTENSITY FROM 45 TO 55 KTS AND A COMPROMISE OF 50 KTS IS CHOSEN
DUE TO THE IMPROVING SATELLITE PRESENTATION.

ISELLE IS MOVING NORTHWEST ...305/14 KT... TOWARD A BREAK IN
THE SUBTROPICAL RIDGE DUE TO A TROUGH IN THE MID-LATITUDES OVER THE
WESTERN UNITED STATES.  THIS TROUGH IS NOT EXPECTED TO BE DEEP
ENOUGH TO RECURVE THE CYCLONE BUT SHOULD SLOW THE FORWARD MOTION
CONSIDERABLY TOMORROW.  THE TRACK IS ONLY SHIFTED SLIGHTLY TO THE
RIGHT OF THE PREVIOUS FORECAST WITH THE BIGGEST CHANGE BEING A 
SLOWER TRACK BEYOND 36 HOURS.  THIS IS IN GOOD AGREEMENT WITH THE 
CONSENSUS OF MODEL GUIDANCE AS THE STORM WILL LIKELY BE IN AN 
ENVIRONMENT OF WEAK STEERING.
 
THE STORM HAS A BRIEF WINDOW OF OPPORTUNITY TO STRENGTHEN TO A
HURRICANE AS THE CURRENT EASTERLY SHEAR IS FORECAST TO RELAX
TOMORROW AND BECOME WESTERLY BY 36 HOURS.  THIS WEAKENING OF THE 
SHEAR IS COINCIDENT WITH THE CYCLONE BEING OVER SSTS BETWEEN 26-27C 
WHICH MAY ALLOW THE STORM TO BECOME A HURRICANE.  IT IS WORTH NOTING 
THAT A SHARPER RECURVATURE WOULD KEEP THE CYCLONE OVER WARMER WATER 
LONGER AND...CONSEQUENTLY...A BIT STRONGER.
 
FORECASTER BLAKE/JARVINEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     17/0300Z 20.4N 112.1W    50 KTS
12HR VT     17/1200Z 21.5N 113.6W    55 KTS
24HR VT     18/0000Z 22.2N 114.6W    65 KTS
36HR VT     18/1200Z 23.0N 115.5W    65 KTS
48HR VT     19/0000Z 23.5N 116.0W    60 KTS
72HR VT     20/0000Z 24.7N 116.7W    50 KTS
 
 
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