[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 091448
TCDAT4

TROPICAL STORM SEAN DISCUSSION NUMBER   6
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL192011
1000 AM EST WED NOV 09 2011

DURING THE PAST FEW HOURS...CONVECTION HAS BECOME BETTER ORGANIZED
IN A BROKEN RING AROUND THE CENTER OF SEAN...WITH THE POSSIBILITY
THAT AN EYE FEATURE IS FORMING.  SUBJECTIVE SATELLITE INTENSITY
ESTIMATES FROM TAFB/SAB ARE 45/55 KT...AND A BLEND OF THESE DATA
GIVES AN INITIAL WIND SPEED OF 50 KT.  SEAN HAS ABOUT 24 TO 36
HOURS OF RELATIVELY LOW SHEAR CONDITIONS...WHICH WOULD SEEM TO
FAVOR SOME INTENSIFICATION.  MODEL GUIDANCE IS A BIT HIGHER...AND
THE OFFICIAL WIND SPEED FORECAST IS RAISED FROM THE LAST ONE...
BETWEEN THE STATISTICAL MODELS AND THE INTENSITY CONSENSUS.  THE
OFFICIAL FORECAST MIGHT BE CONSERVATIVE IF A CENTRAL CORE BECOMES
WELL ESTABLISHED.

THE GRADUAL POLEWARD TURN OF THE CYCLONE HAS BEGUN...WITH AN
INITIAL MOTION ESTIMATE OF 320/3.  SHORTWAVE RIDGING OVER THE
WESTERN ATLANTIC WILL MOVE TO THE EAST LATER TODAY...STEERING SEAN
ON A PATH TOWARD THE NORTH AND NORTH-NORTHEAST BY EARLY TOMORROW.
AS A TROUGH OVER THE EASTERN UNITED STATES APPROACHES THE
STORM...AN INCREASE IN MID-TROPOSPHERIC FLOW SHOULD CAUSE THE
TROPICAL CYCLONE TO ACCELERATE NORTHEASTWARD.  THERE CONTINUES TO
BE A FAIR AMOUNT OF SPREAD...HOWEVER...ON HOW FAR SEAN MOVES FROM
BERMUDA.  THE GFS AND ECMWF HAVE BEEN MORE CONSISTENT THAN THE REST
OF THE GUIDANCE SHOWING A CLOSER TRACK TO BERMUDA...SO THE OFFICIAL
FORECAST WILL STAY NEAR THOSE HISTORICALLY RELIABLE MODELS.  MOST OF
THE GLOBAL MODELS SHOW THIS SYSTEM BEING ABSORBED WITHIN A FRONT
BETWEEN DAY 3 AND DAY 4...AND THE NHC FORECAST CONTINUES TO FOLLOW
THIS SCENARIO.


FORECAST POSITIONS AND MAX WINDS

INIT  09/1500Z 27.9N  70.5W   50 KT  60 MPH
 12H  10/0000Z 28.4N  70.6W   55 KT  65 MPH
 24H  10/1200Z 29.6N  70.2W   55 KT  65 MPH
 36H  11/0000Z 31.5N  68.4W   55 KT  65 MPH
 48H  11/1200Z 33.8N  65.3W   50 KT  60 MPH
 72H  12/1200Z 41.0N  53.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  13/1200Z...ABSORBED

$$
FORECASTER BLAKE



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