966 
 WTPZ42 KNHC 211455
 TCDEP2
 HURRICANE IVO DISCUSSION NUMBER  13
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP122007
 800 AM PDT FRI SEP 21 2007
  
 WHILE BOTH TRMM AND AMSR-E MICROWAVE PASSES FROM AROUND 0900 UTC
 DEPICTED AN EYE FEATURE...CONVENTIONAL SATELLITE IMAGERY SHOWS THAT
 THE OVERALL CLOUD PATTERN OF IVO HAS DETERIORATED.  CLOUD TOPS HAVE
 WARMED AND WESTERLY SHEAR IS STILL IMPINGING UPON THE WESTERN SIDE
 OF THE CYCLONE.  EVEN THOUGH DVORAK CURRENT INTENSITY ESTIMATES FROM
 TAFB AND SAB REMAIN AT 77 KT...PRIMARILY DUE TO CONSTRAINTS...3-
 AND 6-HOURLY ADT INTENSITY ESTIMATES FROM CIMSS ARE ONLY 45-55 KT. 
 BASED ON THE ABOVE...THE INITIAL INTENSITY IS LOWERED TO 65
 KT...WHICH STILL COULD BE GENEROUS.  FIRST LIGHT VISIBLE IMAGERY
 INDICATES THAT THE CENTER OF IVO COULD BE SLIGHTLY TO THE EAST OF
 THE CURRENT ADVISORY LOCATION. 
  
 IVO CONTINUES TO DECELERATE AND THE ESTIMATED MOTION IS NOW 350/6.
 A LARGE MID- TO UPPER-LEVEL LOW DIGGING SOUTHWARD IS CURRENTLY
 CENTERED OFF THE COAST OF SOUTHERN CALIFORNIA...AND A NORTH-SOUTH
 ORIENTED RIDGE IS SITUATED TO THE EAST OF IVO.  THE FORECAST TRACK
 OF IVO IS HIGHLY DEPENDENT UPON THE STRENGTH OF THESE TWO FEATURES.
 THE DYNAMICAL MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT THAT THE
 LOW SHOULD MOVE NORTHEASTWARD IN 36 HOURS OR SO...BUT DISAGREE IN
 HOW MUCH TROUGHING WILL LINGER BEHIND TO MAINTAIN A NORTHWARD TO
 NORTHEAST MOTION OF IVO.  THE HWRF...NOGAPS...AND UKMET MODELS KEEP
 ENOUGH TROUGHING TO INDUCE A MORE NORTHWARD TO NORTHEASTWARD MOTION
 WITH A TRACK ACROSS SOUTHERN BAJA IN 3 OR SO DAYS.  ON THE OTHER
 HAND...THE GFS...ECMWF...AND GFDL SOLUTIONS STALL IVO WELL TO THE
 SOUTHWEST OF THE BAJA PENINSULA.  DUE TO THE UNCERTAINTY...THE
 OFFICIAL TRACK FORECAST IS AN UPDATE OF THE PREVIOUS TRACK AND
 TAKES THE CENTER OF IVO ACROSS THE BAJA PENINSULA IN 72 HOURS OR
 SO...IN LINE WITH THE HWRF...NOGAPS...UKMET SUITE.
  
 BASED ON WATER VAPOR IMAGERY THE WESTERLY SHEAR APPEARS TO BE
 STRONGER THAN THE SHIPS AND DYNAMICAL MODELS ARE INDICATING...AND A
 WEAKENING TREND APPEARS TO BE UNDERWAY. DESPITE THE WARM WATERS...
 THE WESTERLY SHEAR AND POSSIBLY DRY AIR COULD INHIBIT ANY
 RESTRENGTHENING.  THE OFFICIAL INTENSITY FORECAST IS ADJUSTED
 DOWNWARD FROM THE PREVIOUS FORECAST DUE TO THE CURRENT APPEARANCE
 OF THE CYCLONE...AND FOLLOWS A BLEND OF THE SHIPS AND GFDL GUIDANCE.
  
 ONCE AGAIN...GIVEN THE EXTREME UNCERTAINTY PRESENT IN THE OFFICIAL
 FORECAST AT THIS TIME...INTERESTS IN SOUTHERN BAJA CALIFORNIA SHOULD
 CLOSELY MONITOR THE PROGRESS OF IVO.
   
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      21/1500Z 19.5N 113.4W    65 KT
  12HR VT     22/0000Z 20.4N 113.4W    60 KT
  24HR VT     22/1200Z 21.3N 113.1W    60 KT
  36HR VT     23/0000Z 22.1N 112.8W    60 KT
  48HR VT     23/1200Z 23.0N 112.5W    55 KT
  72HR VT     24/1200Z 24.5N 112.0W    50 KT...NEAR BAJA PENINSULA
  96HR VT     25/1200Z 26.0N 111.5W    40 KT...INLAND
 120HR VT     26/1200Z 27.5N 111.5W    30 KT...OVER WATER
  
 $$
 FORECASTER MAINELLI