Hurricane IVO

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HURRICANE IVO DISCUSSION NUMBER   9
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP122007
800 AM PDT THU SEP 20 2007
 
A TRMM PASS AT O9Z SHOWED WELL-DEFINED BUT SLIGHTLY DISPLACED
EYEWALL FEATURES IN THE LOW AND MID LEVELS.  ALTHOUGH SUBJECTIVE
DVORAK INTENSITY ESTIMATES INCREASED TO 77 KT AT 12Z...OBJECTIVE
ADT ESTIMATES FROM CIMSS ACTUALLY HAVE FALLEN AND ARE BELOW
HURRICANE STRENGTH.  THE PRESENTATION IN IR IMAGERY IS RELATIVELY
INDISTINCT.  GIVEN THE MIXED SIGNALS...THE ADVISORY INTENSITY
ESTIMATE WILL REMAIN 65 KT.

BASED ON THE TRMM FIX THE INITIAL MOTION ESTIMATE REMAINS 330/6. A
WEAK MID-LEVEL RIDGE EXTENDS WESTWARD FROM THE SOUTHERN BAJA
PENINSULA...WITH A LARGE DEEP-LAYER CUTOFF LOW OFF THE CALIFORNIA
COAST. IVO IS EXPECTED TO ROUND THIS RIDGE OVER THE NEXT 24
HOURS...BUT AFTER THAT THE FORECAST IS HIGHLY UNCERTAIN. ON ONE
EXTREME IS THE UKMET...WHICH MAINTAINS IVO AS A STRONG SYSTEM AND
CARRIES IT TOWARD SOUTHERN BAJA CALIFORNIA IN THE SOUTHWESTERLY
FLOW ASSOCIATED WITH THE CUTOFF LOW. THE ECMWF REPRESENTS THE
OPPOSITE EXTREME...WEAKENING IVO ABRUPTLY AND BOUNCING IT
SOUTHWESTWARD IN THE LOW-LEVEL FLOW. MOST OF THE DYNAMICAL
MODELS...INCLUDING THE GFS...GFDL...AND HWRF...ARE IN BETWEEN THESE
EXTREMES. THIS GROUP SLOWLY WEAKENS THE HURRICANE AND HAS ONLY A
MODERATE INTERACTION WITH THE SOUTHWESTERLIES...TAKING IVO ON A
TRACK THAT IS SLOWER AND MORE NORTHERLY THAN THE UKMET SOLUTION. 
THE OFFICIAL SOLUTION IS ADJUSTED WESTWARD TO BE IN BETTER
AGREEMENT WITH THIS INTERMEDIATE SOLUTION.  

THE ENVIRONMENT WOULD SEEM TO FAVOR SOME INTENSIFICATION...AT LEAST
UNTIL IVO ROUNDS THE RIDGE.  THE WATER IS WARM AND THE SHEAR IS
LOW..ALTHOUGH THERE IS A STABLE AIR MASS NOT FAR TO THE NORTHWEST
OF IVO.  THE INTENSITY FORECAST BEYOND 24 HOURS IS VERY
UNCERTAIN...AS A TRACK TO THE NORTH OF THE OFFICIAL FORECAST WOULD
BRING IVO UNDER INCREASED SHEAR AND INTO A MORE STABLE ENVIRONMENT. 
THE OFFICIAL FORECAST IS LOWERED SLIGHTLY FROM THE PREVIOUS
ADVISORY BUT IS STILL ABOVE THE OBJECTIVE GUIDANCE MODELS. 
 
INTERESTS IN SOUTHERN BAJA CALIFORNIA SHOULD CLOSELY MONITOR THE
PROGRESS OF IVO DURING THE NEXT FEW DAYS...AND KEEP IN MIND THAT
THERE IS GREAT UNCERTAINTY IN DAY 4 TO 5 FORECASTS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      20/1500Z 17.1N 112.8W    65 KT
 12HR VT     21/0000Z 17.8N 113.2W    70 KT
 24HR VT     21/1200Z 18.8N 113.3W    75 KT
 36HR VT     22/0000Z 19.8N 113.1W    70 KT
 48HR VT     22/1200Z 20.8N 112.6W    65 KT
 72HR VT     23/1200Z 22.5N 111.5W    60 KT
 96HR VT     24/1200Z 24.0N 111.0W    50 KT
120HR VT     25/1200Z 25.5N 110.5W    30 KT
 
$$
FORECASTER FRANKLIN
 
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