ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM SUBTROPICAL STORM ANA DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 PM EDT SUN APR 20 2003 THE PERSISTENT AREA OF LOW PRESSURE LOCATED BETWEEN BERMUDA AND THE EASTERN U.S. HAS SHOWN INCREASED ORGANIZED CONVECTION NEAR THE CENTER DURING THE PAST 24 HR. SATELLITE INTENSITY ESTIMATES ARE SUBTROPICAL 35-40 KT FROM TAFB AND TROPICAL 35 KT FROM SAB. AS THE CYCLONE IS UNDER A SIGNIFICANT UPPER-LEVEL TROUGH...THE SYSTEM WILL BE CALLED A SUBTROPICAL STORM RATHER THAN A TROPICAL STORM. RECENT QUIKSCAT DATA SUPPORT THE ESTIMATES...INDICATING WIDESPREAD 30-40 KT WINDS WITHIN 60-75 NM OF THE CENTER AND PEAK WINDS AS HIGH AS 55 KT. THE STRONGER WINDS MAY BE OVERDONE DUE TO PRECIPITATION...SO THE INITIAL INTENSITY WILL BE SET TO A MORE CONSERVATIVE 35 KT. THE INITIAL MOTION IS 110/9. THE UPPER-LEVEL TROUGH THAT ANA IS EMBEDDED IN IN FORECAST TO MOVE EASTWARD. ADDITIONALLY...THE STORM IS SOUTHWEST OF A BAROCLINIC LOW NEAR 39N60W. THIS COMBINATION SHOULD MOVE THE STORM ON A BASIC EAST-SOUTHEASTWARD TO EASTWARD TRACK. GUIDANCE GENERALLY AGREES WITH THIS SCENARIO... ALTHOUGH THERE ARE SIGNIFICANT DIFFERENCES IN THE SPEED OF MOTION ALONG WITH SOME DIRECTIONAL SPREAD. THE OFFICIAL FORECAST TRACK WILL TAKE THE STORM DOWN THE CENTER OF THE GUIDANCE ENVELOPE IN BEST AGREEMENT WITH THE GFS AND UKMET. ANA IS ONLY THE SECOND KNOWN SUBTROPICAL OR TROPICAL CYCLONE TO FORM IN APRIL...WITH THE OTHER OCCURRING IN 1992. THAT SYSTEM MET ITS DEMISE DUE TO STRONG VERTICAL SHEAR...AND ANA SHOULD DO LIKEWISE AS THE UPPER-LEVEL TROUGH OVER IT OPENS UP AND EXPOSES THE CYCLONE TO THE WESTERLIES. THIS IS FORECAST BY ALL LARGE-SCALE MODELS...AND THE INTENSITY FORECAST THUS CALLS FOR ANA TO WEAKEN AFTER 24 HR. THERE IS ALSO A CHANCE THAT A COLD FRONT ASSOCIATED WITH THE BAROCLINIC LOW TO THE NORTHEAST MAY SWEEP INTO ANA AND DESTROY ITS TROPICAL CHARACTERISTICS. THUS...THE FORECAST OF ANA SURVIVING TO 72 HR MAY BE GENEROUS. IT SHOULD BE NOTED THAT THE FORECAST/ADVISORY IS PROVIDED IN THE 3-DAY FORECAST FORMAT OF 2002 RATHER THAN THE 5-DAY FORECAST FORMAT DEVELOPED FOR THE 2003 SEASON. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 21/0300Z 31.3N 66.0W 35 KTS 12HR VT 21/1200Z 30.8N 64.7W 40 KTS 24HR VT 22/0000Z 30.3N 62.5W 40 KTS 36HR VT 22/1200Z 30.0N 59.8W 35 KTS 48HR VT 23/0000Z 30.0N 56.5W 35 KTS 72HR VT 24/0000Z 30.5N 50.0W 25 KTS...DISSIPATING NNNN
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Page last modified: Monday, 07-Feb-2005 16:49:55 UTC