077 
 WTPZ42 KNHC 081424
 TCDEP2
 TROPICAL DEPRESSION TWELVE-E DISCUSSION NUMBER   2
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
 8 AM PDT WED SEP 08 2004
  
 THERE HAS BEEN A MODEST INCREASE IN THE OVERALL AMOUNT OF DEEP
 CONVECTION OVER THE PAST SEVERAL HOURS...BUT THE BASIC STRUCTURE
 HAS NOT CHANGED.  EASTERLY SHEAR IS KEEPING THE LOW-LEVEL
 CIRCULATION CENTER LOCATED NEAR AND JUST UNDERNEATH THE NORTHEAST
 EDGE OF THE CONVECTION.  DVORAK INTENSITY ESTIMATES RANGE FROM 25
 TO 35 KT FROM THE THREE AGENCIES.  THE QUIKSCAT PASS FROM LATE LAST
 NIGHT SUGGESTED PEAK WINDS WERE AT LEAST 30 KT AND SO THE INITIAL
 INTENSITY ESTIMATE IS INCREASED TO THAT VALUE FOR THIS ADVISORY.
 
 QUIKSCAT AMBIGUITIES AND MORNING MICROWAVE DATA INDICATE THAT THE
 DEPRESSION IS MOVING AT 270/8.  SYNOPTIC STEERING IS BEING PROVIDED
 BY A MID- TO UPPER-LEVEL HIGH OVER BAJA CALIFORNIA THAT IS FORECAST
 BY GLOBAL MODELS TO PERSIST OVER THE NEXT COUPLE OF DAYS...AND THIS
 PATTERN SHOULD RESULT IN A WEST-NORTHWESTERLY TRACK OVER THAT TIME
 FRAME.  BY DAY THREE...THE CYCLONE IS EXPECTED TO BE SOUTH OF A
 WEAKNESS IN THE SUBTROPICAL RIDGE THAT WOULD PROVIDE AN OPPORTUNITY
 FOR A MORE NORTHWARD TRACK.  HOWEVER...NONE OF THE EXPLICIT TRACK
 GUIDANCE TAKES THE CYCLONE INTO THIS WEAKNESS...PERHAPS BECAUSE THE
 MODELS GENERALLY KEEP THE SYSTEM QUITE WEAK THROUGHOUT THE FORECAST
 PERIOD.  ADDITIONAL UNCERTAINTY STEMS FROM A POOR INITIALIZATION OF
 THE LOW-LEVEL VORTEX...WHICH APPEARS TO RESULT IN A SPURIOUS
 NORTHWEST TRACK INITIALLY IN THE GFS AND GFDL.  I AM INCLINED TO
 DISCOUNT THIS NORTHWEST TRACK IN FAVOR OF CONTINUITY WITH THE
 CURRENT MOTION ESTIMATE.  THE OFFICIAL FORECAST IS ADJUSTED SOUTH
 OF THE PREVIOUS ADVISORY FOR THE FIRST 72 HOURS...AND IS SLIGHTLY
 NORTH OF AND SLOWER THAN THE PREVIOUS ADVISORY AFTER THAT. 
 
 CIMSS ANALYSES SHOW 25 KT OF EASTERLY SHEAR OVER THE DEPRESSION. 
 GLOBAL MODELS SUGGEST THAT THIS SHEAR WILL PERSIST OVER THE NEXT 36
 HOURS OR SO...AND THE OFFICIAL FORECAST SHOWS ONLY SLOW
 STRENGTHENING DURING THIS TIME.  SSTS UNDER THE FORECAST TRACK
 DECREASE SLIGHTLY OVER THE NEXT FIVE DAYS...SO IF THE SHEAR
 GRADUALLY DIMINSHES AS EXPECTED THE CYCLONE WILL LIKELY BE SLOW TO
 SPIN DOWN.
 
 FORECASTER FRANKLIN
  
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      08/1500Z 15.2N 111.3W    30 KT
  12HR VT     09/0000Z 15.4N 112.6W    35 KT
  24HR VT     09/1200Z 15.9N 114.5W    40 KT
  36HR VT     10/0000Z 16.5N 116.5W    45 KT
  48HR VT     10/1200Z 17.0N 119.0W    55 KT
  72HR VT     11/1200Z 17.5N 123.5W    55 KT
  96HR VT     12/1200Z 18.0N 129.0W    45 KT
 120HR VT     13/1200Z 18.5N 135.0W    35 KT
  
  
 $$