Subtropical Storm SEAN

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SUBTROPICAL STORM SEAN DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL192011
1100 AM AST TUE NOV 08 2011
 
SEAN APPEARS TO BE MAKING A TRANSITION INTO A MORE TROPICAL SYSTEM
WITH DEEP CONVECTION FORMING IN A CURVED BAND RELATIVELY CLOSE TO
THE CENTER.  THIS IS ALSO REFLECTED IN THE SATELLITE INTENSITY
ESTIMATE FROM TAFB...WHICH USED A CURVED BAND DVORAK PATTERN
INSTEAD OF A SUBTROPICAL CLASSIFICATION.  SINCE SEAN IS STILL NEAR
AN UPPER-LEVEL LOW...I HAVE CHOSEN TO KEEP IT SUBTROPICAL ON THIS
ADVISORY...AND THE WIND SPEED WILL REMAIN 40 KT.  THE CYCLONE WILL
LIKELY BECOME TROPICAL BY THE END OF THE DAY AS MOST OF THE MODEL
GUIDANCE SHOW AN UPPER-LEVEL ANTICYCLONE BUILDING OVER SEAN. SOME
MODEST STRENGTHENING IS ALSO POSSIBLE DURING THE NEXT COUPLE OF
DAYS WHILE THE SHEAR REMAINS LOW TO MODERATE.  THE NHC FORECAST IS
NEAR THE SHIPS/LGEM MODELS...AND A BIT HIGHER THAN THE MODEL
CONSENSUS.  AFTER 48 HOURS...SHEAR SHOULD MARKEDLY INCREASE
AS THE CYCLONE MOVES OVER COOLER WATERS...AND WEAKENING IS LIKELY.  
  
THE CYCLONE HAS BEEN MOVING ERRATICALLY DURING THE PAST SEVERAL
HOURS...RECENTLY ON A SLOW NORTHWARD DRIFT.  SEAN SHOULD BE STEERED
TO THE WEST AND NORTHWEST OVER THE NEXT DAY OR TWO AS SUBTROPICAL
RIDGING BRIEFLY BUILDS OVER THE WESTERN ATLANTIC.  THE STORM WILL
LIKELY TURN TOWARD THE NORTH AND NORTHEAST AWAY FROM THE UNITED
STATES ON THURSDAY DUE TO A DEEP TROUGH MOVING OVER EASTERN NORTH
AMERICA.   THE NHC FORECAST WILL STAY ON THE RIGHT SIDE OF THE
GUIDANCE ENVELOPE...BETWEEN THE GFS AND ECMWF MODELS...AND ASSUME
IT WILL NOT BE ABSORBED BY THAT TROUGH QUITE AS FAST AS MOST OF THE
MODELS SUGGEST.  
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  08/1500Z 27.7N  69.4W   40 KT  45 MPH
 12H  09/0000Z 27.8N  69.7W   45 KT  50 MPH
 24H  09/1200Z 28.2N  70.1W   45 KT  50 MPH
 36H  10/0000Z 29.2N  70.4W   45 KT  50 MPH
 48H  10/1200Z 30.2N  70.4W   45 KT  50 MPH
 72H  11/1200Z 33.5N  66.0W   40 KT  45 MPH
 96H  12/1200Z 40.0N  55.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  13/1200Z...ABSORBED
 
$$
FORECASTER BLAKE
 
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