000
WTNT41 KNHC 092038
TCDAT1
TROPICAL DEPRESSION IGOR DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112010
500 PM AST THU SEP 09 2010
 
THE DEEP CONVECTION THAT WAS LOCATED NEAR THE CENTER EARLIER TODAY
HAS ERODED AND NOW TAKES THE SHAPE OF A CURVED BAND OVER
THE WESTERN SEMICIRCLE...SITUATED ABOUT 90 N MI WEST OF THE CENTER.
THIS ASYMMETRIC CONVECTIVE PATTERN IS DUE TO ABOUT 20-25 KT OF
EASTERLY SHEAR. SINCE THE CONVECTION IS WELL REMOVED FROM THE
CENTER AND BECAUSE EARLIER ASCAT DATA DID NOT SHOW WINDS OF
TROPICAL STORM FORCE...IGOR IS BEING DOWNGRADED TO A TROPICAL
DEPRESSION AT THIS TIME. ALTHOUGH IGOR HAS WEAKENED TODAY...
INTENSIFICATION IS STILL EXPECTED DURING THE FORECAST PERIOD. THE
SHIPS MODEL SHOWS THE SHEAR DECREASING SIGNIFICANTLY DURING THE
NEXT COUPLE OF DAYS.  THIS...IN COMBINATION WITH A RELATIVELY WARM
OCEAN AND MOIST ATMOSPHERE SHOULD ALLOW IGOR TO STRENGTHEN.
HOWEVER...THE CYCLONE WILL BE PASSING THROUGH AN AREA OF SLIGHTLY
COOLER SSTS IN A COUPLE DAYS...SO THE NEW OFFICIAL FORECAST SHOWS A
MORE GRADUAL STRENGTHENING THAN THE PREVIOUS ONE...BUT STILL MAKES
IGOR A HURRICANE IN 3 DAYS.
 
THE LOW-LEVEL CENTER HAS BEEN RACING NORTHWESTWARD DURING
THE LAST FEW HOURS...AND IS NOW LOCATED NORTH OF THE
PREVIOUS FORECAST TRACK. HOWEVER...A WEST-NORTHWESTWARD MOTION IS
EXPECTED TO BEGIN SOON AND PERSIST FOR THE NEXT FEW DAYS AS A LOW-
TO MID-LEVEL RIDGE LOCATED NORTH AND NORTHEAST OF IGOR BECOMES
THE PRIMARY STEERING MECHANISM. THE GLOBAL MODELS SHOW IGOR
APPROACHING A LARGE BUT RATHER FLAT TROUGH IN 4 TO 5 DAYS...WHICH
SHOULD CAUSE THE CYCLONE TO TURN NORTHWESTWARD WITH A DECREASE IN
FORWARD SPEED. THE NEW NHC TRACK FORECAST IS ADJUSTED TO THE NORTH
IN THE SHORT-TERM BUT IS OTHERWISE SIMILAR TO THE PREVIOUS ONE.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      09/2100Z 16.0N  26.4W    30 KT
 12HR VT     10/0600Z 16.7N  27.9W    30 KT
 24HR VT     10/1800Z 17.3N  30.8W    35 KT
 36HR VT     11/0600Z 17.5N  33.9W    45 KT
 48HR VT     11/1800Z 17.8N  36.8W    55 KT
 72HR VT     12/1800Z 18.4N  41.9W    65 KT
 96HR VT     13/1800Z 19.5N  46.0W    75 KT
120HR VT     14/1800Z 21.0N  49.0W    85 KT
 
$$
FORECASTER CANGIALOSI/BRENNAN