ZCZC MIATCDEP1 ALL TTAA00 KNHC DDHHMM TROPICAL STORM SERGIO DISCUSSION NUMBER 6 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP212006 100 AM PST WED NOV 15 2006 MICROWAVE DATA FROM WINDSAT AT 0057Z AND SSM/I AT 0305Z SHOW THAT THE CENTRAL CONVECTION OF SERGIO IS ASYMMETRIC...CURRENTLY CONFINED TO THE EASTERN QUADRANT. THE SHIPS MODEL AND ANALYSES FROM CIMMS AT THE UNIVERSITY OF WISCONSIN INDICATE NORTHWESTERLY SHEAR OF LESS THAN 10 KT...WHICH SEEMS INSUFFICIENT TO EXPLAIN THE CURRENT STRUCTURE. HOWEVER...IT MAY BE SUFFICIENT TO AFFECT THE CIRRUS OUTFLOW...WHICH IS CURRENTLY POOR TO THE NORTHWEST AND FAIR TO GOOD ELSEWHERE. SATELLITE INTENSITY ESTIMATES REMAIN 55 KT FROM TAFB AND SAB...AND THAT REMAINS THE INITIAL INTENSITY. THE INITIAL MOTION IS 135/1. SERGIO IS CURRENTLY IN A REGION OF LIGHT STEERING CURRENTS BETWEEN WEAK MID-LEVEL RIDGES TO THE EAST AND WEST...AND SOUTH OF A DEEP LAYER TROUGH OVER THE CENTRAL UNITED STATES. LARGE-SCALE MODELS FORECAST A MID/UPPER-LEVEL SHORTWAVE TROUGH TO MOVE SOUTHWARD FROM THE WESTERN UNITED STATES AND BECOME A CUTOFF LOW WEST OR SOUTHWEST OF SOUTHERN BAJA CALIFORNIA IN 24-48 HR. THIS SHOULD ALLOW SERGIO TO TURN MORE TOWARD THE NORTH AT A SLIGHTLY FASTER FORWARD SPEED. AFTER 48 HR...THE MODELS DIVERGE ON THE STRENGTH AND TIMING OF AN EAST-WEST RIDGE FORECAST TO FORM OVER NORTHERN MEXICO. THE NOGAPS TAKES SERGIO INLAND OVER MEXICO INTO THE WESTERLIES BEFORE THE RIDGE FORMS. THE UKMET TRAPS THE SYSTEM IN WEAK STEERING CURRENTS SOUTHWEST OF MANZANILLO THROUGH 120 HR... WITH THE OTHER MODELS BETWEEN THESE EXTREMES IN CALLING FOR A NORTH-NORTHWESTWARD MOTION. THE NEW FORECAST TRACK AGREES BEST WITH THE CONU CONSENSUS AND FLORIDA STATE SUPERENSEMBLE MODELS... CALLING FOR A SLOW NORTH-NORTHWESTWARD MOTION FROM 48-120 HR. THE NEW TRACK HAS ONLY MINOR CHANGES FROM THE PREVIOUS FORECAST TRACK. IN THE SHORT TERM...THE LACK OF A CLOSED EYEWALL AND A LESS FAVORABLE OUTFLOW PATTERN SUGGEST A DECREASED CHANCE OF RAPID INTENSIFICATION IN THE NEXT 24 HR OR SO. INDEED...THE SHIPS MODEL NO LONGER CALLS FOR SERGIO TO BECOME A HURRICANE DUE TO INCREASING SHEAR. HOWEVER...THE SHIPS SHEAR APPEARS TOO STRONG COMPARED TO THE FORECAST 200 MB WINDS OF THE GFS...AND THE GFDL AND FSU SUPERENSEMBLE STILL FORECAST SERGIO TO REACH HURRICANE STRENGTH. IN THE LONGER TERM...THE LARGE-SCALE MODELS ALL FORECAST A DIFFLUENT UPPER-LEVEL RIDGE TO FORM NEAR SERGIO FROM 24-72 HR. WHAT THEY DO NOT AGREE ON IS HOW MUCH SHEAR THIS RIDGE WILL PRODUCE. AFTER 72 HR...THE MODELS AGREE THAT SERGIO SHOULD ENCOUNTER INCREASING SHEAR...IF IT IS AS FAR NORTH AS FORECAST. GIVEN THE UNCERTAINTIES...THERE WILL BE NO CHANGE TO THE INTENSITY FORECAST FROM THE PREVIOUS ADVISORY. HOWEVER...THIS IS A LOW CONFIDENCE INTENSITY FORECAST. FORECAST POSITIONS AND MAX WINDS INITIAL 15/0900Z 12.6N 104.2W 55 KT 12HR VT 15/1800Z 12.5N 104.0W 65 KT 24HR VT 16/0600Z 13.1N 103.7W 75 KT 36HR VT 16/1800Z 13.9N 103.7W 80 KT 48HR VT 17/0600Z 15.1N 104.0W 80 KT 72HR VT 18/0600Z 16.5N 104.5W 75 KT 96HR VT 19/0600Z 18.0N 105.5W 65 KT 120HR VT 20/0600Z 19.0N 106.5W 55 KT $$ FORECASTER BEVEN NNNN
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Page last modified: Wednesday, 15-Nov-2006 08:40:04 UTC