176 
 WTPZ42 KNHC 220848
 TCDEP2
 TROPICAL STORM IVO DISCUSSION NUMBER  16
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP122007
 200 AM PDT SAT SEP 22 2007
  
 AFTER SEVERAL HOURS WITHOUT CONVECTION...A SMALL CONVECTIVE CLUSTER
 HAS FORMED TO THE NORTH OF THE CENTER OF IVO.  HOWEVER...WESTERLY
 SHEAR CONTINUES TO AFFECT THE SYSTEM...WITH SATELLITE CLOUD
 MOTIONS INDICATING 20-25 KT OF UPPER-LEVEL WESTERLY FLOW IMPINGING
 ON THE SYSTEM.  SATELLITE INTENSITY ESTIMATES ARE 65 KT FROM TAFB
 AND 55 KT FROM SAB.  BASED ON ON THE DECAY OF THE CLOUD PATTERN AND
 CONTINUITY FROM THE PREVIOUS ADVISORY...THE INITIAL INTENSITY IS
 DECREASED TO 50 KT...AND THIS COULD BE GENEROUS.
 
 THE INITIAL MOTION REMAINS 030/5.  WATER VAPOR IMAGERY INDICATES A
 LARGE MID/UPPER-LEVEL LOW CENTERED JUST WEST OF SOUTHERN
 CALIFORNIA...AND AN EAST-WEST UPPER-LEVEL RIDGE ALONG 15N SOUTH OF
 IVO.  THE LARGE-SCALE MODELS FORECAST THE LOW TO MOVE NORTHEASTWARD
 DURING THE NEXT 24 HOURS...WITH A MID-LEVEL RIDGE BUILDING NEAR OR
 JUST SOUTH OF IVO.  MODEL GUIDANCE REMAINS VERY SPREAD.  THE ECMWF
 TURNS IVO SOUTHWARD AND DISSIPATES IT.  THE GFS STALLS IVO NEAR ITS
 CURRENT LOCATION AND DISSIPATES IT.  THE GFDL AND HWRF FORECAST A
 SLOW MOTION TO THE SOUTHERN BAJA CALIFORNIA PENINSULA IN 2-3 DAYS...
 WHILE THE UKMET AND NOGAPS MOVE THE SYSTEM ACROSS BAJA AND INTO THE
 GULF OF CALIFORNIA.  GIVEN THE CURRENT SLOW MOTION AND SHEAR...THE
 FORECAST TRACK AGAIN CALLS FOR A SLOW NORTHEASTWARD MOTION...
 REACHING BAJA IN 2-3 DAYS.  THE NEW FORECAST TRACK IS AN UPDATE OF
 THE PREVIOUS PACKAGE.
  
 THE LARGE-SCALE MODELS APPARENTLY ARE UNDERFORECASTING THE AMOUNT OF
 SHEAR AFFECTING IVO...WHICH MAKES THE INTENSITY FORECAST A LITTLE
 PROBLEMATIC AS NONE OF THEM ARE FORECASTING SHEAR STRONG ENOUGH TO
 CAUSE SIGNIFICANT WEAKENING.  THE GFDL AND HWRF MAINTAIN IVO AS A
 TROPICAL STORM UNTIL IT REACHES BAJA...WHILE SHIPS WEAKENS IT TO A
 DEPRESSION IN 48 HR.  THE INTENSITY FORECAST CALLS FOR WEAKENING IN
 AGREEMENT WITH THE SHIPS MODEL...AND IF THE CONVECTION DOES NOT
 MAKE A COMEBACK TODAY IVO COULD WEAKEN FASTER THAN CURRENTLY
 FORECAST.
  
 ALTHOUGH IVO IS EXPECTED TO WEAKEN AS IT APPROACHES SOUTHERN BAJA
 CALIFORNIA...TROPICAL STORM WATCHES MAY BE REQUIRED LATER TODAY.
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      22/0900Z 20.9N 112.9W    50 KT
  12HR VT     22/1800Z 21.6N 112.5W    45 KT
  24HR VT     23/0600Z 22.3N 112.0W    40 KT
  36HR VT     23/1800Z 22.8N 111.5W    35 KT
  48HR VT     24/0600Z 23.3N 110.9W    30 KT
  72HR VT     25/0600Z 24.0N 110.0W    25 KT...INLAND
  96HR VT     26/0600Z 24.5N 109.5W    20 KT...REMNANT LOW
 120HR VT     27/0600Z 25.5N 109.5W    20 KT...REMNANT LOW
  
 $$
 FORECASTER BEVEN