000 WTPZ41 KNHC 180835 TCDEP1 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