Tropical Storm ERIN

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TROPICAL STORM ERIN DISCUSSION NUMBER  10
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL052013
500 AM AST SAT AUG 17 2013

THE CENTER OF ERIN IS AT LEAST PARTLY EXPOSED NEAR THE SOUTHWESTERN
EDGE OF THE MAIN CONVECTIVE CLUSTER DUE TO 15 KT OF SOUTHWESTERLY
VERTICAL WIND SHEAR...AND THE CONVECTION IS SOMEWHAT FARTHER FROM
THE CENTER THAN 6 HOURS AGO.  THERE IS NO RECENT DATA FROM NEAR THE
CENTER...SO THE INITIAL INTENSITY IS HELD AT 35 KT...WHICH IS ABOVE
THE SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB.

THE INITIAL MOTION IS 300/13.  THERE IS NO CHANGE TO THE TRACK
FORECAST PHILOSOPHY FROM THE PREVIOUS ADVISORY.  A GRADUALLY
STRENGTHENING SUBTROPICAL RIDGE SHOULD STEER ERIN GENERALLY
WEST-NORTHWESTWARD FOR THE NEXT 24-36 HOUR. THIS SHOULD BE FOLLOWED
BY A 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 BREAK IN THE RIDGE
BETWEEN 50W-60W. THE NEW FORECAST TRACK IS SHIFTED A LITTLE TO THE
NORTH OF THE PREVIOUS TRACK IN BEST AGREEMENT WITH THE ECMWF...
UKMET...CANADIAN..AND NAVGEM MODELS.  THE TRACK LIES WELL TO THE
LEFT OF THE GFS...WHICH RECURVES ERIN THROUGH THE BREAK IN THE
RIDGE.

ERIN IS CURRENTLY OVER SEA SURFACE TEMPERATURES OF 25C-26C.  WHILE
THE FORECAST TRACK TAKES THE CYCLONE OVER WARMER WATER...THE
CYCLONE IS MOVING INTO A VERY DRY MID/UPPER-LEVEL AIR MASS AS SEEN
IN WATER VAPOR AND METEOSAT AIR MASS IMAGERY.  IN ADDITION...THE
SOUTHWESTERLY SHEAR IS EXPECTED TO GRADUALLY INCREASE DURING THE
FORECAST PERIOD.  THE NEW INTENSITY FORECAST IS THE SAME AS THE
PREVIOUS FORECAST IN CALLING FOR ERIN TO WEAKEN TO A DEPRESSION IN
ABOUT 36 HOURS AND TO DEGENERATE TO A REMNANT LOW IN ABOUT 96
HOURS.  AN ALTERNATIVE SCENARIO IS THAT ERIN DISSIPATES EARLIER
THAN CURRENTLY FORECAST...AS SHOWN BY ALL OF THE GLOBAL MODELS
EXCEPT THE GFS.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  17/0900Z 18.9N  35.6W   35 KT  40 MPH
 12H  17/1800Z 19.7N  37.1W   35 KT  40 MPH
 24H  18/0600Z 20.4N  38.9W   35 KT  40 MPH
 36H  18/1800Z 20.9N  40.8W   30 KT  35 MPH
 48H  19/0600Z 21.4N  43.1W   30 KT  35 MPH
 72H  20/0600Z 23.0N  48.0W   30 KT  35 MPH
 96H  21/0600Z 25.5N  52.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  22/0600Z...DISSIPATED
 
$$
FORECASTER BEVEN
 
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