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TROPICAL STORM ISELLE DISCUSSION NUMBER  18
NATIONAL WEATHER SERVICE MIAMI FL
2 AM PDT THU SEP 19 2002
 
ISELLE CONTINUES TO MOVE SLOWLY NORTHEAST TOWARD THE BAJA PENINSULA 
IN RESPONSE TO A MID/UPPER LEVEL TROUGH WEST OF THE CYCLONE...AND 
THE INITIAL MOTION ESTIMATE IS 050/4.  NHC TRACK GUIDANCE IS IN 
GENERAL AGREEMENT WITH A SLOW NORTHEAST MOTION FOR 12-24 
HOURS...FOLLOWED BY A GRADUAL TURN TO THE NORTH THEN NORTHWEST 
THROUGH DISSIPATION IN ABOUT 36 HOURS AS A MID-TROPOSPHERIC RIDGE 
DEVELOPS OVER THE NORTHERN BAJA PENINSULA AND STEERS ISELLE AWAY 
FROM THE BAJA COAST.  THE OFFICIAL FORECAST TRACK IS SLIGHTLY TO THE 
RIGHT OF THE PREVIOUS FORECAST...AND CLOSE TO THAT OF THE GUNS AND 
GUNA CONSENSUS MODELS.  THE OFFICIAL FORECAST BRINGS ISELLE TO ABOUT 
60 NMI FROM CABO SAN LAZARO IN 12-24 HOURS BEFORE TURNING AWAY FROM 
THE COAST BY THE TIME OF DISSIPATION.  

THE AREA OF DEEP CONVECTION WHICH FLARED UP NEAR THE CENTER OF 
ISELLE LATE YESTERDAY HAS BEGUN TO WEAKEN IN THE PAST COUPLE OF 
HOURS.  DVORAK INTENSITY ESTIMATES ARE 35 KT FROM SAB...30 KT FROM 
TAFB...AND 25 KT FROM AFWA.  THE CURRENT INTENSITY WILL BE KEPT AT 
35 KT AS THERE IS STILL A SMALL AREA OF DEEP CONVECTION NEAR THE 
CENTER.  WARM SEA SURFACE TEMPERATURES NEAR THE BAJA COAST AND LIGHT 
SHEAR SHOULD MAINTAIN ISELLE AT MINIMAL TROPICAL STORM INTENSITY FOR 
ABOUT 12 HOURS.  THEREAFTER...THE COMBINATION OF COOLER WATER AND 
INCREASING UPPER LEVEL WESTERLY WINDS SHOULD WEAKEN THE CYCLONE TO 
BELOW TROPICAL STORM STRENGTH AS IT TURNS NORTHWARD AND MAKES ITS 
CLOSEST APPROACH TO LAND.  ISELLE IS FORECAST TO BEGIN DISSIPATING 
IN ABOUT 36 HOURS.  
 
FORECASTER STEWART/MOLLEDA
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     19/0900Z 23.2N 113.1W    35 KTS
12HR VT     19/1800Z 23.5N 112.8W    35 KTS
24HR VT     20/0600Z 24.1N 113.0W    30 KTS
36HR VT     20/1800Z 24.6N 114.0W    25 KTS...DISSIPATING
48HR VT     21/0600Z 25.0N 115.0W    20 KTS...REMNANT LOW
72HR VT     22/0600Z 26.0N 117.0W    20 KTS...REMNANT LOW
 
 
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