268 
 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