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Tropical Storm IVO (Text)

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TROPICAL STORM IVO DISCUSSION NUMBER  15
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP122007
800 PM PDT FRI SEP 21 2007
 
THE CONVECTIVE PATTERN ASSOCIATED WITH IVO HAS RAPIDLY DETERIORATED
OVER THE PAST SEVERAL HOURS WITH THE FORMATION OF A SHARP WESTERN
EDGE AND WARMING CLOUD TOP TEMPERATURES...LIKELY DUE TO INCREASING
SOUTHWESTERLY SHEAR. A FORTUITOUS 0028 UTC SSM/I PASS INDICATED
THAT THE LOW-LEVEL CENTER IS LOCATED WELL TO THE SOUTHWEST OF THE
DEEPEST CONVECTION AND THE INITIAL INTENSITY IS SET AT 55 KT IN
ACCORDANCE WITH A DROP IN T-NUMBERS...BUT THIS ESTIMATE IS PROBABLY
GENEROUS.

IVO IS STILL MOVING RATHER SLOWLY BUT THE SSM/I PASS SUGGESTS THAT
THE SYSTEM HAS TAKEN A SLIGHT TURN TO THE RIGHT OF THE EXTRAPOLATED
TRACK...WITH AN INITIAL MOTION OF 030/5. MODEL GUIDANCE REMAINS
SPLIT IN TWO CAMPS REGARDING THE FORECAST TRACK OF IVO. THE UKMET
AND NOGAPS MODELS REMAIN THE NORTHERN OUTLIERS BY MOVING A DEEP
TROPICAL SYSTEM ACROSS THE SOUTHERN PART OF BAJA CALIFORNIA IN
ABOUT 36-48 HOURS. HOWEVER...CONSIDERING THAT VERTICAL SHEAR HAS
ALREADY BECOME A MAJOR FACTOR IN THE WEAKENING OF IVO...THE
GUIDANCE PROVIDED BY THE GFS...ECMWF...AND GFDL MODELS APPEAR MORE
REASONABLE AT THIS TIME. THESE MODELS MOVE THE SHEARED MID-LEVEL
CIRCULATION OF IVO TO THE NORTHEAST ACROSS BAJA WITH THE LOW-LEVEL
CIRCULATION TURNING EAST AND STAYING SOUTH OF BAJA...POSSIBLY
DISSIPATING IN 3-4 DAYS. THEREFORE...THE OFFICIAL FORECAST IS
ADJUSTED TOWARD THE SOUTHERN CLUSTER OF MODELS AND SHOWS VERY SLOW
MOTION AT DAYS 4 AND 5.

THE INTENSITY FORECAST SHOWS A GRADUAL WEAKENING THROUGH THE
FORECAST PERIOD BUT IS NOT AS FAST AS SHIPS GUIDANCE...JUST IN CASE
THE SYSTEM CONTINUES TO GENERATE CONVECTION AS IT MOVES TOWARDS
BAJA. IF THE SHEAR REALLY IS MAKING A KNOCK-OUT PUNCH...WHICH
APPEARS POSSIBLE GIVEN THE SATELLITE REPRESENTATION...THEN IVO
WOULD WEAKEN FASTER THAN INDICATED IN THE OFFICIAL FORECAST.

ALTHOUGH IVO IS EXPECTED TO WEAKEN AS IT APPROACHES SOUTHERN BAJA
CALIFORNIA...TROPICAL STORM WATCHES MAY BE REQUIRED TOMORROW.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      22/0300Z 20.4N 113.1W    55 KT
 12HR VT     22/1200Z 21.2N 112.8W    50 KT
 24HR VT     23/0000Z 22.0N 112.3W    45 KT
 36HR VT     23/1200Z 22.6N 111.8W    40 KT
 48HR VT     24/0000Z 23.1N 111.3W    35 KT
 72HR VT     25/0000Z 24.2N 110.3W    25 KT...INLAND
 96HR VT     26/0000Z 24.5N 110.0W    25 KT
120HR VT     27/0000Z 25.0N 109.5W    20 KT...REMNANT LOW
 
$$
FORECASTER BERG/BLAKE
 
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