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| #549624 (Received by flhurricane at: 7:53 PM 12.Oct.2012) TCDAT2 TROPICAL STORM RAFAEL SPECIAL DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL172012 730 PM AST FRI OCT 12 2012 A COMBINATION OF SATELLITE AND AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT DATA SHOWS THAT THE LOW PRESSURE SYSTEM IN THE EASTERN CARIBBEAN SEA HAS FORMED A CLOSED CIRCULATION...ALBEIT ONE WITH A LARGE AREA OF LIGHT AND VARIABLE WINDS NEAR THE CENTER. THEREFORE...THE SYSTEM NOW MEETS THE CRITERIA TO BE CONSIDERED A TROPICAL CYCLONE. THE AIRCRAFT REPORTED 1500-FT FLIGHT-LEVEL WINDS OF 43 KT AND SMFR WINDS OF 35 KT NEAR ST. VINCENT...AND BASED ON THESE DATA THE SYSTEM IS UPGRADED TO TROPICAL STORM RAFAEL. MOST OF THE DEEP CONVECTION IS DISPLACED WELL EAST AND SOUTHEAST OF THE CENTER DUE TO ABOUT 20 KT OF SOUTHWESTERLY SHEAR ON THE EAST SIDE OF AN UPPER-LEVEL LOW CENTERED SOUTHWEST OF PUERTO RICO. THE SHIPS MODEL SHOWS THE SHEAR PERSISTING FOR THE NEXT DAY OR SO BEFORE RELAXING A BIT AS THE UPPER-LOW SHEARS OUT AND LIFTS NORTHWARD. ONLY SLOW STRENGTHENING IS EXPECTED DURING THE FORECAST PERIOD. SUBSEQUENTLY...AS THE SHEAR FROM THE UPPER LOW DECREASES...THE CYCLONE BECOMES EMBEDDED IN STRONG SOUTHWESTERLY FLOW AHEAD OF A LONGWAVE TROUGH AMPLIFYING OFF THE U.S. EAST COAST. THE OFFICIAL NHC FORECAST IS CLOSEST TO THE SHIPS MODEL GUIDANCE THROUGH THE PERIOD. GIVEN THE RECENT FORMATION OF THE CENTER...THE INITIAL MOTION ESTIMATE IS A VERY UNCERTAIN 320/8. A GENERAL NORTH-NORTHWESTWARD MOTION IS EXPECTED FOR THE FIRST COUPLE OF DAYS OF THE FORECAST PERIOD AS THE CYCLONE MOVES INTO A WEAKNESS IN THE SUBTROPICAL RIDGE. AT DAYS 3 THROUGH 5 AN ACCELERATION TOWARD THE NORTH AND THEN TOWARD THE NORTH-NORTHEAST IS SHOWN AS A DEEP LAYER TROUGH MOVES OFF THE U.S. EAST COAST. THERE IS A LARGE ALONG-TRACK SPREAD IN THE GUIDANCE LATE IN THE PERIOD. THE GFS...GFS ENSEMBLE MEAN...AND HWRF/GFDL MODELS SHOW THE CYCLONE ACCELERATING AHEAD OF A CLOSED LOW SITUATED OVER THE NORTHEAST U.S. BY DAYS 4 AND 5. THE ECMWF AND UKMET SHOW A MORE PROGRESSIVE UPPER-LEVEL PATTERN SOLUTION THAT FAILS TO CAPTURE THE CYCLONE AS QUICKLY. THE NHC TRACK IS A LITTLE SLOWER THAN THE TVCA MULTI-MODEL CONSENSUS THROUGH THE PERIOD GIVEN THE UNCERTAINTY IN THE FORWARD SPEED...BUT IS FASTER THAN A BLEND OF THE GFS AND ECMWF MODELS. FORECAST POSITIONS AND MAX WINDS INIT 12/2330Z 15.0N 63.1W 35 KT 40 MPH 12H 13/0600Z 16.2N 63.6W 35 KT 40 MPH 24H 13/1800Z 18.0N 64.0W 40 KT 45 MPH 36H 14/0600Z 19.6N 64.4W 45 KT 50 MPH 48H 14/1800Z 21.4N 65.6W 50 KT 60 MPH 72H 15/1800Z 25.0N 67.5W 55 KT 65 MPH 96H 16/1800Z 32.5N 65.0W 55 KT 65 MPH 120H 17/1800Z 43.0N 57.0W 50 KT 60 MPH $$ FORECASTER BRENNAN/BEVEN |
