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| #40215 (Received by flhurricane at: 10:43 AM 17.Aug.2005) TCDAT4 HURRICANE IRENE DISCUSSION NUMBER 52 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 AM EDT WED AUG 17 2005 THE OVERALL CLOUD PATTERN OF IRENE IS BEGINNING TO DETERIORATE AND IS NOW EXPERIENCING WESTERLY SHEAR. AN AVERAGE OF THE DATA T AND CURRENT INTENSITY NUMBERS FROM BOTH TAFB AND SAB WARRANTS BRINGING DOWN THE INITIAL INTENSITY TO 65 KT. THE INITIAL 34 AND 50 KNOT WIND RADII HAVE BEEN ADJUSTED BASED ON A 0935 UTC HIGH RESOLUTION QUIKSCAT PASS. THE INITIAL MOTION ESTIMATE IS A SLIGHTLY FASTER 070/10...AND INDICATES SOME ACCELERATION OVER THE PREVIOUS AVERAGE 6 HOUR MOTION OF 080/8. WATER VAPOR IMAGERY INDICATES A VIGOROUS SHORTWAVE TROUGH HAS MOVED OFF THE MID-ATLANTIC AND NORTHEASTERN U.S. COASTS AND IS SWEEPING RAPIDLY TOWARD IRENE. THIS SAME FEATURE HAS ALSO INTRODUCED THE STRONG WESTERLY MID-TO UPPER-LEVEL SHEAR ON THE SYSTEM. AS THE SHORTWAVE TROUGH AND ASSOCIATED SURFACE FRONT APPROACH IRENE FROM THE WEST...THE HURRICANE IS EXPECTED TO QUICKLY ACCELERATE TO THE NORTHEAST IN RESPONSE TO THE INCREASING SOUTHWESTERLY STEERING FLOW. IRENE IS FORECAST TO MOVE OVER SHARPLY LOWER SSTS WITHIN 24 HOURS...NORTH OF 41N LATITUDE...THE CYCLONE SHOULD QUICKLY DECOUPLE AND BECOME AN EXTRATROPICAL LOW. SINCE THE CYCLONE HAS BEEN CONSISTENTLY SOUTH OF OUR FORECAST TRACK THE EXTRA-TROPICAL TRANSITION HAS BEEN DELAYED TO 36 HOURS. THIS MAY BE SOMEWHAT GENEROUS. BEYOND THAT TIME...EXTRATROPICAL IRENE SHOULD HOOK UP WITH THE MID-LATITUDE WESTERLIES AND RACE OFF TO THE NORTHEAST TOWARD GREENLAND AND ICELAND. THE OFFICIAL TRACK IS SIMILAR TO THE PREVIOUS FORECAST AND IS GOOD AGREEMENT OF THE CONSENSUS OF THE TIGHTLY PACKED NHC MODEL GUIDANCE. ALTHOUGH IRENE IS EXPECTED TO REMAIN OVER 27-28C SSTS FOR ANOTHER 18-24 HOURS OR SO...THE VERTICAL SHEAR IS FORECAST TO GRADUALLY INCREASE AND IRENE IS EXPECTED TO WEAKEN TO A TROPICAL STORM IN 12 HOURS. ONCE IRENE MOVES NORTH OF 41N...THE MUCH COLDER WATER AND STRONG SOUTHWESTERLY SHEAR OF 30-35 KT SHOULD BRING ABOUT A TRANSITION TO AN EXTRATROPICAL CYCLONE. AFTER 48 HOURS...IRENE IS EXPECTED TO BECOME ABSORBED BY A LARGER EXTRATROPICAL LOW. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY AND THE SHIPS INTENSITY MODEL. FORECASTER COBB/PASCH FORECAST POSITIONS AND MAX WINDS INITIAL 17/1500Z 37.1N 58.6W 65 KT 12HR VT 18/0000Z 38.8N 55.6W 60 KT 24HR VT 18/1200Z 43.0N 50.5W 55 KT 36HR VT 19/0000Z 50.5N 44.0W 50 KT...EXTRATROPICAL 48HR VT 19/1200Z 59.5N 36.0W 50 KT...EXTRATROPICAL 72HR VT 20/1200Z...DISSIPATED |
