Tropical Storm SERGIO

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TROPICAL STORM SERGIO DISCUSSION NUMBER  19
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP212006
100 AM PST SAT NOV 18 2006
 
SERGIO CONTINUES TO GENERATE DEEP CONVECTION OVER OR VERY NEAR THE
DIFFICULT TO LOCATE CENTER.  DVORAK INTENSITY ESTIMATES FROM ALL
THREE AGENCIES ARE 45 KT.  AN AMSU PASS AT 0509Z SHOWED A
WELL-DEFINED CURVED BAND IN THE MID LEVELS...BUT WAS NOT CONCLUSIVE
AS TO THE LOW-LEVEL CENTER LOCATION.  A QUIKSCAT PASS AT 00Z
SUPPORTED 35-40 KT WINDS...BUT THAT WAS BEFORE THE LATEST ROUND OF
CONVECTION.  THE ADVISORY INTENSITY IS INCREASED TO 45 KT IN ACCORD
WITH THE SATELLITE ESTIMATES AND THE IMPROVED MICROWAVE
PRESENTATION.

THE INITIAL MOTION IS ESTIMATED TO BE 325/5.  SUBSTANTIAL
WEST-SOUTHWESTERLY SHEAR CONTINUES...SO THE TRACK...AT LEAST IN THE
SHORT RUN...WILL DEPEND ON HOW MUCH CONVECTION THE SYSTEM CAN
MAINTAIN.  GLOBAL MODELS ARE IN PRETTY GOOD AGREEMENT THAT
MID-LEVEL RIDGING WILL BUILD TO THE NORTH OF THE CYCLONE OVER THE
NEXT COUPLE OF DAYS...WHICH SHOULD TURN THE TRACK MORE TO THE WEST. 
HOWEVER...THERE ARE SOME DIFFERENCES IN HOW THE UPPER FLOW OVER
SERGIO EVOLVES AMONG THE GLOBAL MODELS...AND THIS FLOW WILL HAVE A
LOT TO SAY ABOUT HOW THE VERTICALLY COHERENCE OF THE CIRCULATION
EVOLVES.  THE GFS AND ECMWF ARE SHOWING A MORE ZONAL FLOW WITH
STRONGER SHEAR THAN THE UKMET OR NOGAPS MODELS...PARTICULARLY AFTER
ABOUT 24 HOURS.  GIVEN THE PRESENT CONVECTIVE TRENDS...I HAVE
SHIFTED THE TRACK A LITTLE TO THE RIGHT OF THE PREVIOUS FORECAST. 
THE NEW TRACK IS CLOSE TO THE GUNA/CONU/FSSE CONSENSUS.  AT THE
PRESENT TIME...ONLY THE NOGAPS AND GFNI MODELS INDICATE A DIRECT
THREAT TO MEXICO.  HOWEVER...MOISTURE FROM SERGIO WILL CONTINUE TO
STREAM NORTHEASTWARD OVER SOUTHERN MEXICO...WHERE IT COULD INDUCE
SOME DANGEROUS RAINFALLS.

BOTH THE SHIPS AND GFDL MODELS ARE FORECASTING MORE STRENGTHENING...
AND IF THE UKMET/NOGAPS UPPER-LEVEL FLOW FORECASTS ARE CORRECT THIS
COULD HAPPEN. HOWEVER...THE WATER VAPOR IMAGERY AND WINDS SEEM TO
ME TO BE MORE CONSISTENT WITH THE GFS/ECMWF ANALYSIS...SO I AM NOT
WILLING TO MAKE THAT LARGE A CHANGE TO THE PREVIOUS OFFICIAL
FORECAST JUST YET.  HOWEVER...THE CURRENT FORECAST DOES ASSUME THAT
SERGIO WILL BE ABLE TO HOLD ITS OWN AGAINST THE SHEAR FOR ANOTHER
DAY OR SO BEFORE SUCCUMBING.

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      18/0900Z 14.9N 103.3W    45 KT
 12HR VT     18/1800Z 15.5N 103.8W    45 KT
 24HR VT     19/0600Z 16.3N 104.5W    40 KT
 36HR VT     19/1800Z 16.8N 105.8W    35 KT
 48HR VT     20/0600Z 17.0N 107.0W    25 KT
 72HR VT     21/0600Z 17.5N 109.5W    20 KT...REMNANT LOW
 96HR VT     22/0600Z...DISSIPATED
 
$$
FORECASTER FRANKLIN
 
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