ZCZC MIATCDEP1 ALL TTAA00 KNHC DDHHMM TROPICAL STORM SERGIO DISCUSSION NUMBER 23 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP212006 100 AM PST SUN NOV 19 2006 SERGIO REMAINS A SHEARED TROPICAL STORM WITH AN EXPOSED LOW-LEVEL CENTER AND CONVECTION CONFINED TO THE NORTHEASTERN QUADRANT. DVORAK DATA-T NUMBERS FROM ALL AGENCIES HAVE RISEN TO 3.0... CORRESPONDING TO 45 KT. HOWEVER...MUCH OF THE INCREASE IN COLD CLOUD TOPS APPEARS TO BE DUE TO AN EXPANDING CIRRUS CANOPY AND NOT TO ANY SUBSTANTIAL INCREASE IN CONVECTION...SO THE ADVISORY INTENSITY REMAINS 40 KT. WEAKENING REMAINS THE EXPECTATION SINCE THE SOUTHWESTERLY VERTICAL SHEAR IS FORECAST TO INCREASE DURING THE NEXT COUPLE OF DAYS. OCEAN TEMPERATURES ARE NEAR 29 CELSIUS...HOWEVER...SO SERGIO WILL PROBABLY WEAKEN GRADUALLY. THE NEW OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY AND THE LATEST SHIPS GUIDANCE. EVEN THOUGH A MID-LEVEL RIDGE IS IN PLACE TO THE NORTHWEST OF SERGIO...WHICH IS TRYING TO FORCE THE CYCLONE WESTWARD OR WEST-NORTHWESTWARD...THE STRONG UPPER-LEVEL SOUTHWESTERLIES ARE IMPEDING THAT MOTION. THE LOW-LEVEL CENTER HAS MOVED VERY LITTLE DURING THE PAST FEW HOURS...PERHAPS DUE WESTWARD AT ABOUT 2 KT. DURING THE NEXT 24-36 HOURS...MOST OF THE GLOBAL MODELS FORECAST THE RIDGE TO NOT MOVE MUCH...SO THE MOTION OF SERGIO DURING THAT PERIOD WILL PROBABLY DEPEND ON HOW MUCH CONVECTION IT MAINTAINS AND THEREFORE HOW MUCH INFLUENCE THE UPPER-LEVEL SOUTHWESTERLIES HAVE. THE OFFICIAL FORECAST PRESUMES ENOUGH CONVECTION WILL CONTINUE AND CALLS FOR A CONTINUED CRAWL TO THE WEST THROUGH 36 HOURS. THEREAFTER IT IS ASSUMED THE CONVECTION WILL HAVE DECREASED AND THE WEAKENING CYCLONE WILL BE STEERED A LITTLE FASTER BY THE LOW- TO MID-LEVEL EASTERLIES TO THE SOUTH OF THE RIDGE THAT IS FORECAST TO BUILD EASTWARD. SINCE THE TRACK FORECAST HINGES SO MUCH ON HOW LONG THE CONVECTION HANGS ON...AND SINCE THERE IS SUCH DISPARITY IN THE TRACK MODEL GUIDANCE...IT IS HIGHLY UNCERTAIN. THE NEW OFFICIAL TRACK FORECAST IS SOUTH OF AND SLOWER THAN THE PREVIOUS ADVISORY. FORECAST POSITIONS AND MAX WINDS INITIAL 19/0900Z 15.6N 105.2W 40 KT 12HR VT 19/1800Z 15.7N 105.6W 35 KT 24HR VT 20/0600Z 15.8N 106.3W 30 KT 36HR VT 20/1800Z 15.9N 107.2W 30 KT 48HR VT 21/0600Z 16.2N 108.5W 25 KT 72HR VT 22/0600Z 16.5N 111.0W 20 KT...REMNANT LOW 96HR VT 23/0600Z...DISSIPATED $$ FORECASTER KNABB NNNN
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Page last modified: Sunday, 19-Nov-2006 09:00:03 UTC