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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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