000
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