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| #374946 (Received by flhurricane at: 4:40 PM 09.Sep.2010) 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 |
