Tropical Storm ISIS

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TROPICAL STORM ISIS DISCUSSION NUMBER  18
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
8 AM PDT SUN SEP 12 2004
 
A 12/0746Z TRMM PASS DEPICTED THAT THE LOW-LEVEL CIRCULATION CENTER
HAS REMAINED PARTIALLY EXPOSED...ABOUT 20 NM TO THE NORTHEAST OF THE
DEEP CONVECTION.  SATELLITE CURRENT INTENSITY ESTIMATES FROM ALL
AGENCIES REMAIN AT 45 KT. THE INITIAL INTENSITY WILL REMAIN AT 45
KT EVEN THOUGH A TRMM PASS 24 HOURS AGO INDICATED THAT THE LOW
CLOUD LINES WERE BETTER DEFINED THAN THIS MORNING'S IMAGE. THE
SHIPS INTENSITY MODEL CONTINUES TO INDICATE LIGHT 5 KT NORTHEAST TO
EAST SHEAR OVER THE NEXT 36 HOURS. HOWEVER...THE UW-CIMSS WIND
SHEAR ANALYSIS REVEALS 10 TO 20 KT OF EASTERLY SHEAR WHICH
JUSTIFIES THE CURRENT DECOUPLED STRUCTURE OF ISIS. ALTHOUGH THE
SLOW INTENSIFICATION TREND THAT SHIPS AND THE GFDL INDICATE SEEMS
REASONABLE...INCREASING THE INTENSITY TO 60 KT IN 48 HOURS MAY BE A
BIT TOO GENEROUS. THEREFORE...THE INTENSITY TREND FOLLOWS BOTH
MODELS THROUGH THE ENTIRE FORECAST PERIOD BUT IS KEPT AT 55 KT
BEYOND 48 HOURS.
 
THE INITIAL MOTION IS WESTWARD OR 270/9. ALL DYNAMICAL MODELS
CONTINUE TO SHOW A SIGNIFICANT REDUCTION IN SPEED BEYOND 72 HOURS
AS A WEAKNESS DEVELOPS IN THE RIDGE NORTH OF ISIS. THE OFFICIAL
FORECAST CALLS FOR A PERSISTENT WESTWARD MOTION THROUGH THE ENTIRE
FORECAST WITH A SIGNIFICANT DECREASE IN FORWARD SPEED BY DAY 4.
THIS AGREES WITH THE MODEL CONSENSUS AND IS SIMILAR TO THE PREVIOUS
FORECAST. 
 
FORECASTER ROBERTS/BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      12/1500Z 17.4N 123.8W    45 KT
 12HR VT     13/0000Z 17.4N 125.1W    50 KT
 24HR VT     13/1200Z 17.4N 127.0W    50 KT
 36HR VT     14/0000Z 17.4N 129.0W    50 KT
 48HR VT     14/1200Z 17.4N 131.0W    55 KT
 72HR VT     15/1200Z 17.4N 133.0W    55 KT
 96HR VT     16/1200Z 17.4N 134.0W    55 KT
120HR VT     17/1200Z 17.4N 134.5W    55 KT
 
 
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