000 WTNT41 KNHC 202040 TCDAT1 HURRICANE IGOR DISCUSSION NUMBER 51 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010 500 PM AST MON SEP 20 2010 IGOR APPEARS TO BE STARTING EXTRATROPICAL TRANSITION. SURFACE OBSERVATIONS INDICATE THAT A FRONTAL BOUNDARY EXTENDS FROM NEWFOUNDLAND SOUTHWARD TOWARDS THE HURRICANE...AND COLD ADVECTION IS INCREASING OVER THE WESTERN SIDE OF ITS CIRCULATION. GLOBAL MODEL FIELDS SUGGEST THAT IGOR SHOULD BE FULLY INCORPORATED INTO THE FRONTAL ZONE BY 24 HOURS...IF NOT SOONER. ASCAT DATA FROM EARLIER THIS MORNING SHOWED A LARGE AREA OF STRONG WINDS... BETWEEN 55-64 KT...OVER THE SOUTHWESTERN QUADRANT OF THE STORM AND SUPPORTS AN INITIAL INTENSITY OF 65 KT. THE ORIENTATION OF THE STRONG WINDS OVER THE SOUTHWESTERN QUADRANT ALSO SUGGESTS THAT EXTRATROPICAL TRANSITION IS OCCURRING. IGOR COULD BE REINVIGORATED DURING THE NEXT 24 HOURS AS IT BECOMES EXTRATROPICAL...AND THE NHC FORECAST CONTINUES TO SHOW SOME STRENGTHENING IN THE SHORT TERM... FOLLOWED BY GRADUAL WEAKENING AND DISSIPATION BY 120 HOURS. THE INITIAL MOTION IS NOW 040/24. THE TRACK GUIDANCE IS STILL TIGHTLY CLUSTERED FOR THE NEXT 24 HOURS AND THEN SHOWS INCREASING SPREAD AFTER THAT TIME. THERE IS GREATER AGREEMENT THAT IGOR WILL TURN NORTHWARD AND THEN NORTHWESTWARD TOWARD GREENLAND AFTER 24 HOURS...BUT THERE IS NOT AS MUCH AGREEMENT IN THE FORWARD SPEED. THE NEW TRACK FORECAST IS A BLEND OF THE PREVIOUS FORECAST...THE MODEL CONSENSUS TVCN...AND GUIDANCE PROVIDED BY THE OCEAN PREDICTION CENTER. EVEN THOUGH IGOR IS FORECAST TO BE EXTRATROPICAL AS IT PASSES NEWFOUNDLAND...TROPICAL STORM FORCE WINDS COULD REACH THE COAST OF NEWFOUNDLAND BEFORE THE TRANSITION IS COMPLETE. THEREFORE... ENVIRONMENT CANADA HAS ISSUED A TROPICAL STORM WARNING FOR THE EASTERN PART OF THAT PROVINCE. FORECAST POSITIONS AND MAX WINDS INITIAL 20/2100Z 38.2N 61.5W 65 KT 12HR VT 21/0600Z 41.0N 57.9W 70 KT 24HR VT 21/1800Z 45.3N 52.3W 75 KT...POST-TROP/EXTRATROP 36HR VT 22/0600Z 50.1N 47.5W 70 KT...POST-TROP/EXTRATROP 48HR VT 22/1800Z 54.6N 45.8W 60 KT...POST-TROP/EXTRATROP 72HR VT 23/1800Z 60.0N 46.5W 50 KT...POST-TROP/EXTRATROP 96HR VT 24/1800Z 66.0N 56.0W 30 KT...POST-TROP/EXTRATROP 120HR VT 25/1800Z...DISSIPATED $$ FORECASTER BERG