268 
 WTPZ42 KNHC 121435
 TCDEP2
 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
  
  
 $$