Tropical Storm IVO

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TROPICAL STORM IVO DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP122007
200 AM PDT WED SEP 19 2007

IVO CONTINUES TO STRENGTHEN AS IT EXHIBITS A FAIRLY SYMMETRIC CDO 
AND WELL-DEFINED UPPER-LEVEL OUTFLOW PATTERN.  THE CURRENT
INTENSITY IS SET AT 50 KT...WHICH IS THE AVERAGE OF DVORAK ESTIMATES
FROM TAFB AND SAB.  MICROWAVE IMAGERY SHOWS A DEVELOPING INNER CORE
BUT NO EYE...YET.  IT IS EXPECTED THAT THE TROPICAL CYCLONE WILL
REMAIN AN ENVIRONMENT OF LOW VERTICAL WIND SHEAR AND HIGH OCEANIC
HEAT CONTENT FOR THE NEXT COUPLE OF DAYS.  THUS THE OFFICIAL
INTENSITY FORECAST SHOWS STRENGTHENING TO A HURRICANE IN A DAY OR
TWO.  THIS IS IN REASONABLE AGREEMENT WITH THE LATEST GFDL MODEL
PREDICTION.  THE SHIPS GUIDANCE IS A LITTLE HIGHER THAN THE
OFFICIAL FORECAST THROUGH 72 HOURS.  BY DAYS 4 AND 5...AN INCREASE
IN WESTERLY SHEAR IS LIKELY TO CAUSE SOME WEAKENING AND THE
OFFICIAL FORECAST IS QUITE SIMILAR TO THE SHIPS OUTPUT IN THE LATTER
PART OF THE PERIOD.  IF IVO MOVES FARTHER NORTH THAN EXPECTED IT
WOULD ENCOUNTER STRONGER UPPER-LEVEL WESTERLIES...AND WOULD MOST
LIKELY WEAKEN FASTER THAN INDICATED HERE.

THERE HAS BEEN A SLIGHT SLOWING IN THE ESTIMATED MOTION...WHICH IS
NOW ABOUT 300/9.  DURING THE NEXT 48-72 HOURS...IVO IS FORECAST TO
MOVE AROUND THE WESTERN PERIPHERY OF A MID-LEVEL SUBTROPICAL
ANTICYCLONE.  BEYOND THAT TIME FRAME...GLOBAL MODELS DEPICT A
STRONG MID- TO UPPER-TROPOSPHERIC LOW DROPPING SOUTHWARD AND
SOUTHEASTWARD INTO SOUTHERN CALIFORNIA AND NORTHERN BAJA
CALIFORNIA.  IN RESPONSE TO THIS FEATURE MOST OF THE DYNAMICAL
TRACK MODELS TURN IVO NORTHEASTWARD OR...IN THE CASE OF THE GFDL
MODEL... EAST-NORTHEASTWARD...IN 3 TO 5 DAYS.  THE OFFICIAL
FORECAST IS SHIFTED A LITTLE TO THE EAST OF THE PREVIOUS ONE AND IS
CLOSE TO THE GUNA DYNAMICAL TRACK MODEL CONSENSUS.  AS NOTED
EARLIER...THE TRACK FORECAST AT 3-5 DAYS IS HIGHLY UNCERTAIN
BECAUSE THERE IS A  LARGE SPREAD IN THE CREDIBLE NUMERICAL GUIDANCE
AT THAT TIME RANGE.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      19/0900Z 14.7N 110.0W    50 KT
 12HR VT     19/1800Z 15.4N 111.2W    55 KT
 24HR VT     20/0600Z 16.4N 112.5W    60 KT
 36HR VT     20/1800Z 17.3N 113.4W    65 KT
 48HR VT     21/0600Z 18.2N 113.8W    65 KT
 72HR VT     22/0600Z 20.0N 113.5W    60 KT
 96HR VT     23/0600Z 21.0N 112.5W    55 KT
120HR VT     24/0600Z 21.5N 112.0W    50 KT
 
$$
FORECASTER PASCH
 
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