782 
 WTNT44 KNHC 082035
 TCDAT4
  
 TROPICAL STORM SEAN DISCUSSION NUMBER   3
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL192011
 500 PM AST TUE NOV 08 2011
  
 CONVECTION HAS FORMED NEAR THE CENTER OF SEAN THIS AFTERNOON WITH A
 BANDING FEATURE PERSISTING IN THE NORTHEASTERN QUADRANT.  SINCE THE
 STORM IS A LITTLE FARTHER FROM THE UPPER-LEVEL LOW...WITH A WARM
 CORE APPARENT ON AMSU ANALYSES AND A SMALLER RADIUS OF MAXIMUM
 WINDS AS SEEN IN ASCAT DATA...SEAN NOW HAS ENOUGH CHARACTERISTICS
 TO BE CONSIDERED TROPICAL.  THE MAXIMUM WINDS ARE SET TO 45 KT...IN
 AGREEMENT WITH THE TAFB DVORAK ESTIMATE AND EARLIER ASCAT WINDS. 
 WHILE THE REGIONAL HURRICANE MODELS DO NOT SHOW MUCH
 INTENSIFICATION OF SEAN...THE SHEAR REMAINS RELATIVELY LIGHT FOR
 THE NEXT 36 HR OR SO WHILE THE SYSTEM IS OVER MARGINAL SSTS.  SINCE
 THE STORM IS EMBEDDED WITHIN COLDER-THAN-AVERAGE UPPER-AIR
 TEMPERATURES...THE SST THRESHOLD FOR TROPICAL CYCLONE STRENGTHENING
 IS LOWER THAN USUAL...AND SOME FURTHER STRENGTHENING IS
 ANTICIPATED.  THE NEW NHC FORECAST IS HIGHER THAN THE PREVIOUS
 ONE...AND REMAINS IN LINE WITH THE SHIPS/LGEM MODELS AND THE
 EXPERIMENTAL SPC3 ENSEMBLE SHIPS GUIDANCE.  IN ABOUT TWO DAYS...
 SEAN SHOULD ENCOUNTER A MORE HOSTILE UPPER-AIR ENVIRONMENT...WHICH
 SHOULD INDUCE WEAKENING.  
  
 THE CENTER OF THE CYCLONE HAS BEEN WOBBLING AROUND FOR QUITE SOME
 TIME...BUT IT APPEARS THAT A MOTION TOWARD THE WEST-NORTHWEST HAS
 BEGUN.  THIS GENERAL TRACK IS EXPECTED TO CONTINUE THROUGH TOMORROW
 AS A RIDGE MOVES THROUGH THE WESTERN ATLANTIC.  THEREAFTER...THE
 STORM SHOULD TURN TOWARD THE NORTH AND NORTHEAST BY THURSDAY AHEAD
 OF A DEEP TROUGH OVER THE EASTERN UNITED STATES.  IT SEEMS THAT
 BEING ON THE RIGHT SIDE OF THE GUIDANCE EARLIER WAS A GOOD CALL...
 AS MOST OF THE MODELS HAVE SHIFTED IN THAT DIRECTION...APPARENTLY
 BECAUSE OF FLATTER MID-LATITUDE FLOW FORECAST TO AFFECT SEAN.  ONLY
 COSMETIC CHANGES WERE MADE TO THE NHC TRACK FOR THE FIRST COUPLE OF
 DAYS...WITH A SHIFT TO THE SOUTHEAST MADE AT DAY 3...BETWEEN THE
 ECMWF AND GFS MODELS.  ALL OF THE GLOBAL MODELS SHOW THE STORM
 BEING ABSORBED BY A FRONTAL BOUNDARY BY DAY 4...AND THIS SCENARIO
 IS REFLECTED IN THE NHC FORECAST.  
  
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  08/2100Z 27.8N  69.8W   45 KT  50 MPH
  12H  09/0600Z 27.9N  70.2W   50 KT  60 MPH
  24H  09/1800Z 28.4N  70.4W   50 KT  60 MPH
  36H  10/0600Z 29.0N  70.5W   55 KT  65 MPH
  48H  10/1800Z 29.9N  69.7W   50 KT  60 MPH
  72H  11/1800Z 34.0N  64.0W   45 KT  50 MPH
  96H  12/1800Z...ABSORBED
  
 $$
 FORECASTER BLAKE