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Tropical Storm SERGIO

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TROPICAL STORM SERGIO DISCUSSION NUMBER  22
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP212006
700 PM PST SAT NOV 18 2006
 
AFTER A BRIEF WANE IN THE CONVECTIVE PATTERN...A NEW SMALL BURST OF
CONVECTION HAS FORMED NEAR AND NORTHEAST OF THE LOW-LEVEL CENTER.
DVORAK SATELLITE CLASSIFICATIONS HAVE DECREASED SLIGHTLY...AND THE
CURRENT INTENSITY IS A BLEND OF T3.0 AND T2.5 DVORAK INTENSITY
ESTIMATES FROM TAFB AND SAB...RESPECTIVELY.
 
THE INITIAL MOTION ESTIMATE IS 295/05 KT. THERE IS NO SIGNIFICANT
CHANGE TO THE PREVIOUS FORECAST TRACK OR REASONING. SERGIO IS
EXPECTED TO MOVE WEST-NORTHWESTWARD TO WESTWARD ALONG THE SOUTHERN
PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE SITUATED TO THE NORTH
OF THE CYCLONE THROUGHOUT THE FORECAST PERIOD. THE FORWARD SPEED IS
EXPECTED TO BE SLIGHTLY LESS THAN THAT OF THE GFDL MODEL FORECAST
DUE TO SOUTHWESTERLY UPPER-LEVEL WINDS IMPEDING THE WESTWARD MOTION
SOMEWHAT. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS
TRACK AND REMAINS NEAR THE SOUTHERN EDGE OF THE GUIDANCE ENVELOPE
IN BEST AGREEMENT WITH THE GFDL...GFS...GFS ENSEMBLE...AND ECMWF
MODEL TRACKS.

GRADUAL WEAKENING IS EXPECTED AS SOUTHWESTERLY VERTICAL SHEAR IS
FORECAST TO EXCEED 30 KT WITHIN THE NEXT 12-18 HOURS. WITH SERGIO
REMAINING OVER 29C SSTS...THERE MAY BE OCCASIONAL BRIEF CONVECTIVE
BURSTS THAT WILL MAINTAIN THE SYSTEM AS A MARGINAL TROPICAL CYCLONE
FOR THE NEXT 48 HOURS OR SO. HOWEVER...BY 72 HOURS SERGIO IS
EXPECTED TO MOVE OVER COOLER SSTS AND EVENTUALLY SUCCUMB TO THE
EFFECTS OF HOSTILE SHEAR CONDITIONS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      19/0300Z 15.7N 105.1W    40 KT
 12HR VT     19/1200Z 16.1N 105.8W    35 KT
 24HR VT     20/0000Z 16.5N 106.7W    35 KT
 36HR VT     20/1200Z 16.8N 107.8W    30 KT
 48HR VT     21/0000Z 17.1N 109.1W    25 KT...DISSIPATING
 72HR VT     22/0000Z 17.5N 111.6W    20 KT...REMNANT LOW
 96HR VT     23/0000Z...DISSIPATED
 
$$
FORECASTER STEWART
 
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