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| #376896 (Received by flhurricane at: 11:03 PM 17.Sep.2010) TCDAT1 HURRICANE IGOR DISCUSSION NUMBER 40 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010 1100 PM AST FRI SEP 17 2010 INFRARED SATELLITE IMAGERY INDICATES IGOR HAS BECOME BETTER ORGANIZED WITH A RING OF CONVECTIVE CLOUD TOPS OF -70C AND COLDER ENCIRCLING A 20-25 NMI DIAMETER EYE THAT HAS BECOME MORE DISTINCT DURING THE PAST COUPLE OF HOURS. A 17/2026Z AMSU OVERPASS ALSO INDICATED THE UPPER-LEVEL WARM CORE HAS STRENGTHENED AND MOVED UPWARD FROM 300 MB TO THE 200 MB...SUGGESTING THAT IGOR IS LIKELY STRENGTHENING. AN AIR FORCE RESERVE RECON AIRCRAFT WILL BE INVESTIGATING IGOR AROUND 06Z AND PROVIDE A BETTER INTENSITY ESTIMATE. THE INITIAL MOTION ESTIMATE IS 315/11. IGOR HAS MADE A TROCHOIDAL WOBBLE TO THE RIGHT OF THE PREVIOUS FORECAST TRACK...BUT THIS IS LIKELY JUST A TEMPORARY MOTION. IGOR IS EXPECTED TO MOVE BACK ON OR CLOSE TO THE PREVIOUS ADVISORY TRACK BASED ON 00Z UPPER-AIR DATA FROM BERMUDA SHOWING 24-HOUR MID-LEVEL HEIGHTS HAVE INCREASED BY 20 METERS AND WINDS HAVE SHIFTED AROUND TO AN EASTERLY DIRECTION... WHICH INDICATES THE SUBTROPICAL RIDGE HAS BUILT WESTWARD TO THE NORTH OF BERMUDA. UNFORTUNATELY...THIS RIDGING PATTERN WILL BE SHORT-LIVED DUE TO A STRONG SHORTWAVE TROUGH CURRENTLY LOCATED JUST OFF THE U.S. EAST COAST FORECAST BY ALL THE GLOBAL AND REGIONAL MODELS TO CONTINUE TO MOVE EASTWARD AND CREATE A WEAKNESS IN THE RIDGE BETWEEN 60W-70W LONGITUDE BY 24 HOURS. THIS WILL ALLOW IGOR TO GRADUALLY MOVE NORTHWARD THROUGH THIS BREAK IN THE SUBTROPICAL RIDGE PATTERN AND PASS VERY CLOSE TO BERMUDA IN ABOUT 48 HOURS. BY 72 HOURS...IGOR IS FORECAST TO BE CAPTURED BY A SECOND SHORTWAVE TROUGH AND BE ACCELERATED OVER THE FAR NORTH ATLANTIC AS A POWERFUL EXTRATROPICAL LOW PRESSURE SYSTEM. THE OFFICIAL FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY AND IS CLOSE TO THE MODEL CONSENSUS. IGOR IS EXHIBITING AN IMPRESSIVE OUTFLOW PATTERN THAT CONTINUES TO EXPAND IN ALL QUADRANTS. THE HURRICANE IS EXPECTED TO MAINTAIN THIS FAVORABLE OUTFLOW REGIME FOR THE NEXT 36-48 HOURS. AFTERWARDS... INCREASING SOUTHWESTERLY UPPER-LEVEL FLOW AHEAD OF A MID- TO UPPER-LEVEL TROUGH WILL INCREASE THE SHEAR ACROSS THE CYCLONE... WHICH COUPLED WITH DECREASING SSTS...SHOULD INDUCE WEAKENING. BY 96 HOURS...IGOR IS FORECAST TO TRANSITION INTO A LARGE AND POWERFUL EXTRATROPICAL CYCLONE OVER THE FAR NORTH ATLANTIC WHEN IGOR MERGES WITH A FRONTAL SYSTEM. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE SHIPS INTENSITY MODEL. THE EXTRATROPICAL FORECAST TRACK AND INTENSITIES AT 96 AND 120 HOURS IS BASED ON GUIDANCE FROM THE NOAA OCEAN PREDICTION CENTER. FORECAST POSITIONS AND MAX WINDS INITIAL 18/0300Z 24.6N 62.0W 95 KT 12HR VT 18/1200Z 25.6N 63.2W 100 KT 24HR VT 19/0000Z 27.1N 64.4W 105 KT 36HR VT 19/1200Z 29.1N 65.0W 105 KT 48HR VT 20/0000Z 31.7N 64.5W 100 KT 72HR VT 21/0000Z 36.2N 61.2W 85 KT 96HR VT 22/0000Z 45.0N 50.0W 65 KT...POST-TROP/EXTRATROP 120HR VT 23/0000Z 52.5N 42.0W 65 KT...POST-TROP/EXTRATROP $$ FORECASTER STEWART |
