000 WTNT44 KNHC 081443 TCDAT4 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