ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM TROPICAL STORM DARBY DISCUSSION NUMBER 2 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 8 PM PDT MON JUL 26 2004 THE DEPRESSION IS UPGRADED TO A TROPICAL STORM ON THE BASIS OF T2.5 DVORAK CLASSIFICATIONS FROM TAFB AND SAB. OVER THE PAST SEVERAL HOURS...THERE HAS BEEN A GRADUAL INCREASE IN DEEP CONVECTION CLOSE TO AND NORTH OF THE PRESUMED CENTER OF CIRCULATION...AND SOME BANDING IS STILL EVIDENT IN THE WESTERN SEMICIRCLE. THERE IS GOOD OUTFLOW IN THE NORTHWEST QUADRANT BUT NONE IS EVIDENT ELSEWHERE. THE CIRCULATION OF DARBY APPEARS TO BE IN ITS FORMATIVE STAGE...STILL ELONGATED AND NOT YET HAVING CLEANLY SEPARATED FROM THE ITCZ. THIS SUGGESTS THAT DEVELOPMENT OVER THE NEXT DAY OR SO SHOULD BE MORE GRADUAL RATHER THAN RAPID. THE GFDL AND SHIPS MODELS...ON THE OTHER HAND...TAKE DARBY TO HURRICANE STRENGTH IN 24-36 HOURS. THE OFFICIAL FORECAST...WHILE MORE AGGRESSIVE THAN THE PREVIOUS ADVISORY...TAKES 48 HOURS TO REACH THAT THRESHOLD. THE INITIAL MOTION REMAINS DIFFICULT TO DETERMINE...BUT IS ESTIMATED TO BE 280/12. I DON'T HAVE A GREAT DEAL OF CONFIDENCE IN THE MODEL SOLUTIONS TONIGHT. CURIOUSLY...MOST OF THE DYNAMICAL GUIDANCE CALLS FOR AN IMMEDIATE NORTHWESTWARD MOTION. THE MODELS MAY BE REACTING TO A MID- TO UPPER-LEVEL LOW AHEAD OF DARBY NEAR 21N/122W...OR PERHAPS HAVE A POOR INITIALIZATION OF THE LOW-LEVEL STEERING FLOW. THERE ARE ALSO SUGGESTIONS IN THE GLOBAL MODELS THAT THE UPPER-LOW COULD END UP WEAKENING THE SUBTROPICAL RIDGE NORTH OF DARBY IN A COUPLE OF DAYS...YET THE MODELS TEND TO BEND THE TRACK BACK TO THE WEST ABOUT THIS TIME. IT'S USUALLY A LOSING PROPOSITION TO TRY TO OUT-INTEGRATE THE GLOBAL GUIDANCE...SO THE OFFICIAL FORECAST ATTEMPTS TO ACCOMODATE THIS GUIDANCE WITH A SHORT-TERM BEND TO THE RIGHT FOLLOWED BY A MORE WESTWARD TRACK. I WOULD NOT BE SURPRISED HOWEVER...IF IT TURNS OUT THAT DARBY MOVES MORE WESTWARD INITIALLY AND THEN TURNS NORTHWESTWARD IN A COUPLE OF DAYS. FORECASTER FRANKLIN FORECAST POSITIONS AND MAX WINDS INITIAL 27/0300Z 12.5N 116.1W 35 KT 12HR VT 27/1200Z 13.1N 117.7W 40 KT 24HR VT 28/0000Z 13.9N 119.6W 45 KT 36HR VT 28/1200Z 14.5N 121.5W 55 KT 48HR VT 29/0000Z 15.0N 123.5W 65 KT 72HR VT 30/0000Z 15.5N 127.5W 65 KT 96HR VT 31/0000Z 16.0N 131.5W 65 KT 120HR VT 01/0000Z 16.5N 135.5W 60 KT $$ NNNN
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Page last modified: Tuesday, 27-Jul-2004 02:32:27 UTC