000
WTNT41 KNHC 090837
TCDAT1
TROPICAL STORM IGOR DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112010
500 AM AST THU SEP 09 2010
 
THE CLOUD PATTERN HAS DETERIORATED DURING THE PAST 6 HOURS AND
CONTINUES TO BE HIGHLY SHEARED.  NEITHER SATELLITE INTENSITY
ESTIMATES NOR ASCAT MEASUREMENTS SUPPORT TROPICAL STORM INTENSITY.
THE INITIAL INTENSITY HAS BEEN ADJUSTED DOWN TO 35 KNOTS AND THIS
ESTIMATE IS GENEROUS. IGOR COULD WEAKEN A LITTLE MORE TODAY BUT
GIVEN THAT THE CYCLONE STILL HAS A LARGE CIRCULATION AND IS MOVING
TOWARD A MORE FAVORABLE ENVIRONMENT OF LOWER SHEAR AND WARMER
OCEAN...A GRADUAL STRENGTHENING COULD BEGIN IN 24 HOUR OR SO.  IGOR
IS STILL FORECAST TO BECOME A HURRICANE IN ABOUT 3 DAYS.
 
FIRST VISIBLE SATELLITE IMAGES INDICATE THAT THE CENTER IS STILL
LOCATED SOUTH OF THE CAPE VERDE ISLANDS SUGGESTING THAT IGOR HAS
BEEN MEANDERING DURING THE PAST FEW HOURS. HOWEVER...THE LARGE
CIRCULATION SHOULD BEGIN TO MOVE SLOWLY TOWARD THE WEST-NORTHWEST
LATER TODAY. THE STEERING PATTERN OVER THE ATLANTIC HAS BEEN QUITE
PERSISTENT AND CONSISTS OF A SUBTROPICAL RIDGE OVER THE EASTERN
PART OF THE BASIN AND A BROAD TROUGH OSCILLATING BETWEEN THE
EASTERN UNITED STATES AND THE WESTERN PORTION OF THE BASIN. THIS
STEERING PATTERN WHICH IS FORECAST BY THE GLOBAL MODELS TO
CONTINUE...WOULD FAVOR A GENERAL WESTWARD MOTION WITH AN INCREASE
IN FORWARD SPEED DURING THE NEXT DAY OR TWO AND THEN A TURN MORE TO
THE WEST-NORTHWEST BY THE END OF THE FORECAST PERIOD. TRACK
GUIDANCE DEPICTS THIS SCENARIO WHICH IS REFLECTED IN THE OFFICIAL
FORECAST.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      09/0900Z 13.8N  24.3W    35 KT
 12HR VT     09/1800Z 14.0N  25.3W    30 KT
 24HR VT     10/0600Z 15.0N  28.0W    40 KT
 36HR VT     10/1800Z 16.0N  31.0W    45 KT
 48HR VT     11/0600Z 16.5N  34.0W    55 KT
 72HR VT     12/0600Z 17.0N  40.0W    65 KT
 96HR VT     13/0600Z 18.0N  44.5W    75 KT
120HR VT     14/0600Z 19.5N  49.0W    85 KT
 
$$
FORECASTER AVILA