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Tropical Storm IGOR


ZCZC MIATCDAT1 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM IGOR DISCUSSION NUMBER  10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112010
500 PM AST FRI SEP 10 2010
 
THE UPPER-LEVEL SHEAR THAT HAS BEEN PLAGUING IGOR FOR THE PAST
SEVERAL DAYS HAS FINALLY STARTED TO ABATE AND CIRRUS OUTFLOW HAS
NOW BECOME PRONOUNCED IN ALL QUADRANTS. HOWEVER...SOME MID-LEVEL
SHEAR AND DRY AIR ENTRAINMENT IS STILL AFFECTING THE CYCLONE...
WHICH HAS RESULTED IN A VERY ASYMMETRIC CONVECTIVE CLOUD PATTERN
WITH THE LOW-LEVEL CENTER DISPLACED AT LEAST 30 NMI TO THE EAST OF
THE COLDEST CLOUD TOPS. INTENSITY ESTIMATES ARE 30 KT FROM SAB...55
KT FROM TAFB...AND UW-CIMSS 3-HR AVERAGE ADT VALUES OF 49 KT AND
AMSU ESTIMATES OF 53 KT. THE INITIAL INTENSITY HAS BEEN
CONSERVATIVELY INCREASED TO 40 KT...WHICH WILL BE TOO LOW IF THE
LOW-LEVEL CENTER IS ACTUALLY CLOSER TO THE DEEP CONVECTION.

THE INITIAL MOTION IS 280/18. THERE IS NO CHANGE TO THE PREVIOUS
TRACK FORECAST OR REASONING. IGOR IS EXPECTED TO MOVE WESTWARD...
ACCOMPANIED BY A GRADUAL DECREASE IN FORWARD SPEED...FOR THE NEXT 96
HOURS AS THE CYCLONE MOVES ALONG THE SOUTHERN PERIPHERY OF A LARGE
AND STRONG SUBTROPICAL RIDGE SITUATED TO THE NORTH. BY DAY 5...A
BROAD LONGWAVE TROUGH IS FORECAST TO MOVE OFF THE U.S. EAST COAST
AND CREATE A WEAKNESS IN THE RIDGE TO THE NORTHEAST OF THE LESSER
ANTILLES. THIS SHOULD CAUSE THE STEERING FLOW TO WEAKEN AND ALLOW
WHAT IS EXPECTED TO BE A LARGE HURRICANE IGOR AT THAT TIME TO
GRADUALLY TURN WEST-NORTHWESTWARD. THE LATEST MODEL GUIDANCE IS
MORE TIGHTLY PACKED AROUND THE PREVIOUS NHC TRACK...ESPECIALLY AT
DAYS 4 AND 5.  IN PARTICULAR...THE GFDL AND ECMWF SHOW LESS OF A
NORTHWARD TURN THAT MIGHT BE RELATED TO A FLATTER LONGWAVE TROUGH
IN THE LATEST GLOBAL RUNS.  THE OFFICIAL FORECAST TRACK REQUIRES
LITTLE CHANGE AND IS AN EXTENSION OF THE PREVIOUS ADVISORY.
 
THE VERTICAL SHEAR IS EXPECTED TO CONTINUE TO DECREASE TO 5 TO 10 KT
FOR THE NEXT 5 DAYS. THIS FAVORABLE UPPER-LEVEL ENVIRONMENT...IN
CONJUNCTION WITH SSTS INCREASING TO 29C BY THE END OF THE FORECAST
PERIOD...SHOULD RESULT IN STEADY INTENSIFICATION. IGOR IS EXPECTED
TO REACH HURRICANE STATUS BY SUNDAY AND MAJOR HURRICANE STATUS BY
DAYS 4 OR 5. THIS SCENARIO IS SUPPORTED BY THE SHIPS...LGEM...
HWRF...AND GFDL MODELS. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      10/2100Z 16.7N  33.3W    40 KT
 12HR VT     11/0600Z 16.8N  35.4W    45 KT
 24HR VT     11/1800Z 17.1N  38.4W    50 KT
 36HR VT     12/0600Z 17.2N  41.0W    60 KT
 48HR VT     12/1800Z 17.3N  43.4W    70 KT
 72HR VT     13/1800Z 17.7N  47.8W    80 KT
 96HR VT     14/1800Z 18.7N  51.6W    90 KT
120HR VT     15/1800Z 20.0N  55.0W   105 KT
 
$$
FORECASTER STEWART
 
NNNN


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Page last modified: Friday, 15-Apr-2011 12:09:14 UTC