Tropical Storm ISIS

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TROPICAL DEPRESSION ISIS DISCUSSION NUMBER  14
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
8 AM PDT SAT SEP 11 2004
 
AN EARLIER AMSU-B DEPICTED THAT ISIS WAS EXPOSED TO THE
NORTHEAST OF THE DEEP CONVECTION. ENHANCED BD-CURVE ANIMATION
INDICATES A NEW DEEP BURST OF CONVECTION ABOUT 50 NM SOUTHWEST OF
THE LOW-LEVEL CIRCULATION CENTER. SATELLITE CURRENT INTENSITY
ESTIMATES ARE 30 KT FROM TAFB AND AFWA...25 KT FROM SAB. A 11/0200Z
QUIKSCAT PASS REVEALED UN-FLAGGED 30 KT WINDS BENEATH THE EASTERN
EDGE OF THE CONVECTION. THEREFORE THE INTENSITY REMAINS AT 30 KT.
THE SHIPS MODEL SHOWS WEAK NORTHEASTERLY SHEAR THROUGH 72
HOURS...HOWEVER...UW-CIMSS WIND SHEAR ANALYSIS DEPICTS 10 TO 20 KT
OF EASTERLY SHEAR. ALTHOUGH THE INTENSITY TREND FROM THE SHIPS AND
THE GFDL INTENSITY FORECASTS SEEMS REASONABLE...THE ACTUAL
INTENSITY VALUES MAY BE SLIGHTLY HIGH. THE GFDL ALSO INCREASES THE
INTENSITY TO 60 KT IN 24 HOURS. SEA SURFACE TEMPERATURE ANALYSIS
REVEALS WARM WATERS ABOVE 26 DEGREES CELSIUS SOUTH OF 20 N. BASED
ON AN IMPROVING ENVIRONMENT ALOFT AND WARM WATERS...THE FORECAST
INTENSITY IS CLOSE TO THE PREVIOUS FORECAST AND SLIGHTLY LOWER THAN
THE AFOREMENTIONED MODELS. 
 
THE INITIAL MOTION IS WESTWARD OR 280/9. LARGE SCALE MODELS AGREE
WITH STRENGTH AND ORIENTATION OF A MID-UPPER RIDGE EXTENDING FROM
MEXICO/BAJA THROUGH 48 HOURS. AFTERWARD...GUIDANCE SUGGESTS THAT A
MID-UPPER LEVEL TROUGH EXTENDING SOUTHWEST FROM BAJA WILL CAUSE A
REDUCTION IN MOTION BEYOND 72 HOURS. THE OFFICIAL FORECAST IS
SIMILAR TO THE PREVIOUS FORECAST...HOWEVER...WEIGHED MORE HEAVILY
ON THE MODEL CONSENSUS WITH A REDUCTION IN SPEED BEYOND 72 HOURS.
 
FORECASTER ROBERTS/AVILA
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      11/1500Z 17.8N 120.2W    30 KT
 12HR VT     12/0000Z 17.8N 121.5W    30 KT
 24HR VT     12/1200Z 17.8N 123.5W    35 KT
 36HR VT     13/0000Z 17.8N 125.2W    40 KT
 48HR VT     13/1200Z 17.8N 126.9W    45 KT
 72HR VT     14/1200Z 18.0N 130.0W    45 KT
 96HR VT     15/1200Z 18.0N 132.0W    45 KT
120HR VT     16/1200Z 18.0N 134.0W    45 KT
 
 
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