608 
 WTPZ42 KNHC 222029
 TCDEP2
 TROPICAL STORM IVO DISCUSSION NUMBER  18
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP122007
 200 PM PDT SAT SEP 22 2007
 
 THE INTENSITY AND EXTENT OF DEEP CONVECTION HAS DIMINISHED OVER THE
 PAST SEVERAL HOURS...AND THERE IS LITTLE EVIDENCE OF BANDING
 FEATURES.  LATEST DVORAK CLASSIFICATIONS FROM TAFB AND SAB ARE AT
 T3.0 OR 45 KT.  HOWEVER...AN EARLIER QUIKSCAT PASS SUGGESTS THAT IVO
 COULD STILL HAVE A FEW SPOTS OF 50 KT WINDS SO THE INTENSITY IS HELD
 AT 50 KT FOR THIS ADVISORY.  GRADUAL WEAKENING IS LIKELY AS
 SOUTHWESTERLY SHEARING INCREASES OVER THE CYCLONE.  IVO COULD
 WEAKEN BELOW TROPICAL STORM STRENGTH BEFORE REACHING THE BAJA
 CALIFORNIA PENINSULA.  IN FACT...THE GFS...THE U.K. MET. OFFICE 
 AND ECMWF GLOBAL MODELS PREDICT DISSIPATION JUST TO THE SOUTH OR
 SOUTHWEST OF THE SOUTHERN TIP OF BAJA.
 
 VISIBLE IMAGES MAKE IT EASIER TO ESTIMATE THE CENTER LOCATION AND
 THE INITIAL MOTION IS A SLOW 030/4.  THE MID- TO UPPER-LEVEL CYCLONE
 NEAR SOUTHERN CALIFORNIA IS GRADUALLY LIFTING NORTHEASTWARD...BUT A
 LINGERING TROUGH TO THE SOUTHWEST SHOULD PROVIDE ENOUGH STEERING
 FLOW TO CARRY THE TROPICAL CYCLONE SLOWLY NORTH-NORTHEASTWARD TO
 NORTHEASTWARD OVER THE NEXT COUPLE OF DAYS.  THE OFFICIAL TRACK
 FORECAST IS QUITE SIMILAR TO THAT OF THE PREVIOUS ADVISORY.  THIS
 IS ALSO IN CLOSE AGREEMENT WITH A CONSENSUS OF THE LATEST GFDL AND
 HWRF PREDICTIONS.
 
 OWING TO THE UNCERTAINTY IN INTENSITY FORECASTS...A TROPICAL STORM
 WATCH HAS BEEN ISSUED FOR A PORTION OF THE WEST COAST OF THE BAJA
 CALIFORNIA PENINSULA...SOUTH OF 24.5N.
 
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      22/2100Z 21.8N 112.5W    50 KT
  12HR VT     23/0600Z 22.2N 112.2W    45 KT
  24HR VT     23/1800Z 22.9N 111.6W    40 KT
  36HR VT     24/0600Z 23.6N 110.9W    35 KT
  48HR VT     24/1800Z 24.2N 110.4W    30 KT
  72HR VT     25/1800Z 25.0N 110.0W    25 KT
  96HR VT     26/1800Z 26.0N 110.0W    20 KT...REMNANT LOW
 120HR VT     27/1800Z 27.0N 110.0W    20 KT...REMNANT LOW
  
 $$
 FORECASTER MAINELLI/PASCH