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Tropical Storm ERIN Forecast Discussion Number 9
2013-08-17 04:30:55| National Hurricane Center (Atlantic)
Issued at 1100 PM AST FRI AUG 16 2013 000 WTNT45 KNHC 170230 TCDAT5 TROPICAL STORM ERIN DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052013 1100 PM AST FRI AUG 16 2013 THUNDERSTORMS HAVE MARKEDLY INCREASED NEAR THE CENTER OF ERIN DURING THE PAST FEW HOURS. THE CENTER APPEARS TO BE ON THE SOUTHWESTERN EDGE OF A LARGE COLD CLOUD SHIELD...WHICH IS CONSISTENT WITH A SOUTHWESTERLY SHEAR ENVIRONMENT. SHIP MGSG6 PASSED NEAR THE CENTER RECENTLY AND REPORTED SUSTAINED WINDS OF 40 KT. A REVIEW OF THE HISTORY OF THE SHIP WIND DATA SUGGESTS THE REPORT IS PROBABLY A FEW KNOTS TOO HIGH...BUT IT EASILY SUPPORTS A 35 KT INITIAL INTENSITY. CONVECTION WILL LIKELY FLUCTUATE DURING THE NEXT DAY OR SO WHILE ERIN MOVES OVER MARGINALLY WARM WATERS AND IN A MODERATE SHEAR ENVIRONMENT. WEAKENING SHOULD OCCUR BY 36H DUE TO AN INCREASE IN SHEAR...WHICH WOULD PROMOTE THE MIXING OF VERY DRY AIR ALOFT INTO THE CENTER OF THE CYCLONE. ALTHOUGH THE SSTS NOTABLY INCREASE IN A FEW DAYS...A COMBINATION OF THE DRY ENVIRONMENT...STRONG SHEAR AND UPPER-LEVEL CONVERGENCE WILL PROBABLY CAUSE ERIN TO DEGENERATE INTO A REMNANT LOW BY 96H. THIS SOLUTION IS CONSISTENT WITH THE RELIABLE GLOBAL MODELS...ALTHOUGH MOST OF THESE MODELS DISSIPATE THE CYCLONE EVEN EARLIER THAN THE NEW NHC FORECAST. ERIN APPEARS TO BE MOVING TO THE NORTHWEST AT ABOUT 14 KT... ALTHOUGH THE CENTER IS HARDER TO LOCATE NOW DUE TO ALL OF THE CONVECTION. A GRADUAL TURN TOWARD THE WEST-NORTHWEST IS EXPECTED AS ERIN ENCOUNTERS A REBUILDING SUBTROPICAL RIDGE. THE CYCLONE SHOULD TURN MORE TO THE LEFT AROUND A STRONGER LOW-LEVEL RIDGE THROUGH 72H. THEREAFTER...A TURN BACK TO THE NORTHWEST IS FORECAST WHEN ERIN...OR ITS REMNANTS...MOVES TOWARD A WEAKNESS IN THE RIDGE. THE NEW NHC FORECAST IS VERY CLOSE TO THE PREVIOUS ONE THROUGH 36H...THEN IS SHIFTED WESTWARD NEAR A CONSENSUS OF THE UKMET... GFS...ECMWF...AND FLORIDA STATE SUPERENSEMBLE GUIDANCE AFTER THAT TIME. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 18.5N 34.5W 35 KT 40 MPH 12H 17/1200Z 19.5N 36.1W 35 KT 40 MPH 24H 18/0000Z 20.2N 38.1W 35 KT 40 MPH 36H 18/1200Z 20.7N 39.9W 30 KT 35 MPH 48H 19/0000Z 21.0N 42.2W 30 KT 35 MPH 72H 20/0000Z 22.0N 47.0W 30 KT 35 MPH 96H 21/0000Z 24.5N 51.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 22/0000Z...DISSIPATED $$ FORECASTER BLAKE
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