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| #373008 (Received by flhurricane at: 10:59 PM 01.Sep.2010) TCDAT4 TROPICAL STORM GASTON DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL092010 1100 PM AST WED SEP 01 2010 GASTON HAS MAINTAINED A WELL-DEFINED CURVED BAND OF CONVECTION THAT WRAPS FROM THE WESTERN TO NORTHERN SIDES OF THE CIRCULATION...AND DVORAK FINAL-T NUMBERS ARE T2.5/35 KT FROM BOTH TAFB AND SAB. THE OBJECTIVE ADT ESTIMATE FROM UW-CIMSS IS CURRENTLY T3.3/51 KT...BUT A RECENT 0013 UTC ASCAT PASS SHOWS WINDS NO HIGHER THAN 25-30 KT. THE INITIAL INTENSITY IS KEPT AT 35 KT AS A BLEND OF THESE ESTIMATES. THE OFFICIAL INTENSITY FORECAST HAS AGAIN BEEN INCREASED A BIT FROM THE PREVIOUS ADVISORY. ALTHOUGH THERE IS SOME DRY AIR SURROUNDING THE CYCLONE...GLOBAL MODEL GUIDANCE SUGGESTS THAT THE VERTICAL SHEAR SHOULD REMAIN LOW...AT LEAST FOR THE NEXT 2-3 DAYS...AND THIS COULD PREVENT THE DRY AIR FROM HAVING A SIGNIFICANT EFFECT. STILL...THERE IS A LOT OF UNCERTAINTY IN THE INTENSITY FORECAST GIVEN THE DIFFERENCES BETWEEN THE DYNAMICAL AND STATISTICAL MODELS. OVER THE NEXT 5 DAYS...THE GFDL AND HWRF ONLY STRENGTHEN GASTON TO A STRONG TROPICAL STORM OR MINIMAL HURRICANE...THE SHIPS MODEL MAKES IT A CATEGORY 2 HURRICANE...AND THE LGEM BRINGS IT TO CATEGORY 4 INTENSITY. THE OFFICIAL FORECAST IS A LITTLE ABOVE THE INTENSITY CONSENSUS FOR THE FIRST 48 HOURS WHEN ENVIRONMENTAL CONDITIONS SHOULD BE MOST IDEAL AND THEN VERY CLOSE TO THE CONSENSUS THEREAFTER WHEN EASTERLY SHEAR COULD INCREASE A BIT. THE LATEST SATELLITE FIXES INDICATE THAT GASTON HAS BEGUN TO SLOW DOWN...POSSIBLY DUE TO A MID-LEVEL TROUGH LOCATED TO ITS NORTHWEST. IT IS ALSO A LITTLE FARTHER NORTH THAN PREVIOUSLY ESTIMATED AND HAS AN INITIAL MOTION OF 280/10 KT. WITH THE BREAK IN THE SUBTROPICAL RIDGE...GASTON IS EXPECTED TO CONTINUE TO SLOW DOWN OVER THE NEXT COUPLE OF DAYS. THE MULTI-MODEL CONSENSUS TVCN IS SLOWER THAN THE PREVIOUS FORECAST...SO THE NEW OFFICIAL FORECAST SHOWS A SLOWER MOTION OVER THE NEXT 36 HOURS...BUT IS STILL ON THE SAME GENERAL TRACK AS THE PREVIOUS ADVISORY. BY DAYS 4 AND 5...THE RIDGE IS EXPECTED TO STRENGTHEN...AND THE CYCLONE SHOULD BEGIN TO MOVE FASTER TO THE WEST. FORECAST POSITIONS AND MAX WINDS INITIAL 02/0300Z 13.4N 37.7W 35 KT 12HR VT 02/1200Z 13.5N 38.5W 40 KT 24HR VT 03/0000Z 13.7N 39.7W 45 KT 36HR VT 03/1200Z 13.8N 40.8W 50 KT 48HR VT 04/0000Z 14.0N 42.1W 55 KT 72HR VT 05/0000Z 14.5N 45.5W 65 KT 96HR VT 06/0000Z 15.0N 49.5W 75 KT 120HR VT 07/0000Z 16.0N 54.5W 85 KT $$ FORECASTER BERG |
