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Tropical Storm SERGIO (Text)

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TROPICAL STORM SERGIO DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP212006
700 PM PST TUE NOV 14 2006
 
SATELLITE IMAGERY SUGGEST THAT SERGIO HAS CONTINUED TO STRENGTHEN
DURING THE LAST FEW HOURS...AND THE INITIAL INTENSITY IS SET AT 55
KT IN LINE WITH DVORAK INTENSITY ESTIMATES FROM BOTH TAFB AND SAB.  
IN THE SHORT-TERM...THE CYCLONE IS EXPECTED TO BE LOCATED WITHIN A
FAVORABLE ENVIRONMENT FOR ADDITIONAL STRENGTHENING AND INTENSITY
GUIDANCE IS IN GOOD AGREEMENT IN MAKING SERGIO A CATEGORY ONE
HURRICANE WITHIN 48 HOURS.  THEREAFTER...THE INTENSITY FORECAST
GETS TRICKY AS THE ANTICIPATED TRACK OF SERGIO WOULD TAKE THE
CYCLONE INTO AN INCREASINGLY SHEARED ENVIRONMENT.  AS A
RESULT...THE INTENSITY GUIDANCE DIVERGES CONSIDERABLY. THE GFDL
MODEL INDICATES ADDITIONAL STRENGTHENING MAKING SERGIO A STRONG
CATEGORY THREE HURRICANE IN 3-4 DAYS WHILE THE SHIPS AND FSU
SUPERENSEMBLE SHOW WEAKENING BACK TO A TROPICAL STORM.  SINCE THE
GFDL MODEL CAN SOMETIMES BE RATHER INSENSITIVE TO VERTICAL
SHEAR...THE OFFICIAL FORECAST IS CLOSER TO THE LATTER MODELS.   
 
SERGIO HAS SHOWN LITTLE OR NO MOTION DURING THE LAST 6 HOURS AND IS
EXPECTED TO REMAIN IN A VERY WEAK STEERING PATTERN OVER THE NEXT
DAY OR SO.  THEREAFTER...THE CYCLONE IS EXPECTED TO GRADUALLY BEGIN
MOVING NORTHWARD...ALBEIT SLOWLY...AS A WEAK MID-LATITUDE TROUGH
DROPS SOUTHEASTWARD OVER THE BAJA PENINSULA AND A WEAK RIDGE FORMS
OVER SOUTHERN MEXICO.  UNFORTUNATELY...THE DYNAMICAL MODELS DO NOT
AGREE ON THE EXACT EVOLUTION OF THE LARGE-SCALE STEERING PATTERN
AND THERE IS CONSIDERABLE SPREAD AMONG THE AVAILABLE TRACK MODELS. 
FURTHER COMPLICATING THE TRACK FORECAST IS UNCERTAINTY IN THE
INTENSITY OR DEPTH OF THE CYCLONE AS ANY APPRECIABLE NORTHWARD
MOTION WOULD TAKE SERGIO INTO AN INCREASINGLY SHEARED ENVIRONMENT.
A STRONG AND DEEP CYCLONE WOULD TEND TO MOVE NORTHWARD TOWARD
SOUTHWESTERN MEXICO AS SHOWN BY THE GFDL. CONVERSELY...A WEAK AND
SHALLOW CYCLONE WOULD TEND TO TURN TOWARDS THE WEST-NORTHWEST AS
SHOWN BY THE GFS AND ITS ENSEMBLE MEAN.  SINCE THE GFS DOES NOT
APPEAR TO HAVE A REPRESENTATIVE VORTEX AND THE GFDL'S INTENSITY
APPEARS TOO STRONG GIVEN THE ANTICIPATED VERTICAL SHEAR...THE
OFFICIAL FORECAST LIES IN BETWEEN THESE TWO SOLUTIONS AND IS IN
CLOSE AGREEMENT WITH THE FSU SUPERENSEMBLE.  THE NEW TRACK FORECAST
IS A LITTLE TO THE EAST AND SLOWER THAN THAT FROM THE PREVIOUS
ADVISORY. 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      15/0300Z 12.8N 104.3W    55 KT
 12HR VT     15/1200Z 12.8N 104.2W    65 KT
 24HR VT     16/0000Z 13.1N 103.7W    75 KT
 36HR VT     16/1200Z 13.6N 103.5W    80 KT
 48HR VT     17/0000Z 14.6N 103.6W    80 KT
 72HR VT     18/0000Z 16.5N 104.5W    75 KT
 96HR VT     19/0000Z 17.5N 105.5W    65 KT
120HR VT     20/0000Z 18.5N 106.5W    55 KT
 
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