ZCZC MIATCDEP1 ALL TTAA00 KNHC DDHHMM TROPICAL STORM SERGIO DISCUSSION NUMBER 15 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP212006 100 AM PST FRI NOV 17 2006 SERGIO APPEARS TO BE SHEARING APART THIS MORNING...WITH THE LOW-LEVEL CENTER AT LEAST PARTLY EXPOSED ON THE WEST SIDE OF THE REMAINING DEEP CONVECTION. ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN SHOW ABOUT 20 KT OF SOUTHWESTERLY SHEAR AT THE PRESENT TIME. WHILE SATELLITE INTENSITY ESTIMATES AT 06Z WERE STILL AT HURRICANE STRENGTH...THE SATELLITE SIGNATURE HAS DECREASED SIGNIFICANTLY SINCE THEN...AND THUS SERGIO IS DOWNGRADED TO A TROPICAL STORM. THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 350/3. WATER VAPOR IMAGERY INDICATES A BROAD MID/UPPER-LEVEL LOW NEAR 20N112W...WITH BROAD MID/UPPER-LEVEL RIDGING DEVELOPING NORTH OF THE LOW NEAR NORTHERN BAJA CALIFORNIA. THE LARGE-SCALE MODELS FORECAST THE LOW TO MOVE WESTWARD UNDER THE RIDGE...WITH THE RIDGE BUILDING EASTWARD AND SOUTHEASTWARD INTO CENTRAL MEXICO. THE TRACK GUIDANCE IS SPLIT ROUGHLY INTO TWO CLUSTERS. THE FIRST... WHICH INCLUDES THE CONU... THE FSU SUPERENSEMBLE...THE NOGAPS...AND THE GFDL...CALL FOR A TURN TOWARD THE NORTHWEST DURING THE NEXT 24 HOURS...WITH THAT MOTION CONTINUING THROUGH THE FORECAST PERIOD. THE SECOND...WHICH INCLUDES THE GFS...THE GFS ENSEMBLE MEAN...THE UKMET...AND THE BAM SHALLOW...CALLS FOR A GENERAL WEST-NORTHWESTWARD MOTION. THE OFFICIAL FORECAST IS AN UPDATE OF THE PREVIOUS PACKAGE AND IS DOWN THE MIDDLE OF THE FIRST CLUSTER. HOWEVER...IF SERGIO TOTALLY SHEARS APART LOW-LEVEL STEERING WILL BECOME PREDOMINANT LEADING TO A TRACK SIMILAR TO THE SECOND CLUSTER. SOME ADJUSTMENT OF THE FORECAST TRACK MAY BE NECESSARY LATER TODAY DEPENDING ON HOW THE STRUCTURE OF SERGIO EVOLVES. WHILE SERGIO IS CURRENTLY IN A RATHER UNFAVORABLE ENVIRONMENT...THE LARGE-SCALE MODELS CONTINUE TO SUGGEST THAT THE SHEAR WILL DECREASE SLIGHTLY DURING THE NEXT 48 HR...ACCOMPANIED BY AN INCREASE IN UPPER-LEVEL DIVERGENCE. BASED ON THIS...THE INTENSITY FORECAST WILL CALL FOR THE CURRENT WEAKENING TO STOP IN 12-24 HR. THIS PART OF THE INTENSITY FORECAST IS SIMILAR TO...BUT WEAKER THAN...THE SHIPS AND SUPERENSEMBLE MODELS. AFTER 48 HR...THE LARGE-SCALE MODELS AGREE THAT THE SHEAR WILL INCREASE SIGNIFICANTLY...WHICH SHOULD CAUSE WEAKENING AND EVENTUAL DISSIPATION BY 120 HR. IF THE CURRENT SHEAR NOT DECREASE...SERGIO MAY DISSIPATE EARLIER THAN CURRENTLY FORECAST. THE WIND RADII WERE ADJUSTED IN THE BASIS OF A 0100Z QUIKSCAT OVERPASS. RAINBANDS CONTINUE TO AFFECT THE MEXICAN COAST...AND INTERESTS IN SOUTHWESTERN MEXICO SHOULD CONTINUE TO MONITOR THE PROGRESS OF SERGIO. FORECAST POSITIONS AND MAX WINDS INITIAL 17/0900Z 14.0N 102.8W 60 KT 12HR VT 17/1800Z 14.6N 103.0W 55 KT 24HR VT 18/0600Z 15.2N 103.5W 50 KT 36HR VT 18/1800Z 15.9N 104.4W 50 KT 48HR VT 19/0600Z 16.7N 105.4W 50 KT 72HR VT 20/0600Z 18.0N 107.0W 40 KT 96HR VT 21/0600Z 19.5N 109.5W 30 KT 120HR VT 22/0600Z 21.0N 112.0W 25 KT...REMNANT LOW $$ FORECASTER BEVEN NNNN
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Page last modified: Friday, 17-Nov-2006 08:50:03 UTC