000
WTNT41 KNHC 130835
TCDAT1
HURRICANE IGOR DISCUSSION NUMBER  21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112010
500 AM AST MON SEP 13 2010
 
IGOR REMAINS A POWERFUL AND WELL ORGANIZED HURRICANE WITH A
SYMMETRIC EYEWALL...CLOUD TOPS COLDER THAN -70 C...A 15 N MI
CIRCULAR EYE...AND SPIRAL RAINBANDS.  SATELLITE CLASSIFICATIONS
FROM ALL AGENCIES HAVE NOT CHANGED MUCH FROM 0000 UTC...AND
THEREFORE THE INITIAL INTENSITY IS HELD AT 130 KT FOR THIS
ADVISORY.  AS IS COMMON FOR MAJOR HURRICANES IN FAVORABLE OCEANIC
AND ATMOSPHERIC ENVIRONMENTS...INTERNAL DYNAMICS WILL LIKELY GOVERN
THE INTENSITY CHANGE OF IGOR DURING THE NEXT DAY OR TWO.  SINCE IT
APPEARS THAT AN EYEWALL REPLACEMENT CYCLE HAS NOT YET BEGUN...THE
OFFICIAL FORECAST WILL ALLOW FOR A LITTLE MORE STRENGTHENING TODAY. 
THEREAFTER...A GRADUAL WEAKENING IS SHOWN FOLLOWING THE TREND IN
THE INTENSITY GUIDANCE.  IGOR IS FORECAST TO MOVE INTO AN AREA OF
STRONGER SHEAR BY THE END OF THE PERIOD...WHICH SHOULD CAUSE A
LITTLE MORE WEAKENING. 
 
THE HURRICANE CONTINUES TO MOVE WESTWARD AT 11 KT...AND IS ON THE
PREVIOUS FORECAST TRACK.  IGOR IS EXPECTED TO TURN WEST-
NORTHWESTWARD IN ABOUT 24 HOURS AND THEN NORTHWESTWARD IN A
COUPLE OF DAYS AS IT APPROACHES A BROAD TROUGH OVER THE CENTRAL AND
WESTERN ATLANTIC.  ALTHOUGH MOST OF THE GLOBAL MODELS SHOW THE
TROUGH FLATTENING IN 3 TO 4 DAYS...THERE ARE DISAGREEMENTS IN HOW
MUCH...IF ANY...SUBTROPICAL RIDGING BUILDS IN THE WAKE OF THE
TROUGH.  THE ECMWF AND UKMET MODELS CONTINUE TO BUILD MORE RIDGING
NORTH OF IGOR...RESULTING IN A TRACK FARTHER WEST THAN THE OTHER
MODELS.  OVERALL...THE MODEL GUIDANCE HAS SHIFTED SLIGHTLY TO THE
RIGHT FROM THE LAST CYCLE AND THE OFFICIAL FORECAST IS NUDGED IN
THAT DIRECTION...BUT REMAINS ON THE SOUTH SIDE OF THE GUIDANCE
ENVELOPE.

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      13/0900Z 17.7N  48.8W   130 KT
 12HR VT     13/1800Z 17.9N  50.2W   140 KT
 24HR VT     14/0600Z 18.5N  51.8W   135 KT
 36HR VT     14/1800Z 19.3N  53.4W   130 KT
 48HR VT     15/0600Z 20.4N  54.9W   125 KT
 72HR VT     16/0600Z 22.5N  57.7W   120 KT
 96HR VT     17/0600Z 25.0N  60.0W   115 KT
120HR VT     18/0600Z 28.0N  63.0W   105 KT
 
$$
FORECASTER CANGIALOSI