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| #40169 (Received by flhurricane at: 4:34 AM 17.Aug.2005) TCDAT4 HURRICANE IRENE DISCUSSION NUMBER 51 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 AM EDT WED AUG 17 2005 THE LAST COUPLE OF SSMI AND TRMM OVERPASSES CLEARLY INDICATE THAT IRENE HAS SLOWED ITS FORWARD SPEED...AND THAT MID- TO UPPER-LEVEL WESTERLY SHEAR HAS ERODED THE EYE FEATURE AND HAS TILTED IT EASTWARD OF THE LOW-LEVEL CENTER BY AT LEAST 30 NMI. SATELLITE INTENSITY ESTIMATES HAVE ALSO COME DOWN...SO THE INTENSITY HAS BEEN DECREASED TO 75 KT FOR THIS ADVISORY. THE INITIAL MOTION ESTIMATE IS 080/7...EVEN THOUGH THE MOTION OVER THE PAST 9 HOURS HAS BEEN 090/06. A VIGOROUS SHORTWAVE TROUGH MOVING QUICKLY EASTWARD OFF THE MID-ATLANTIC AND NORTHEASTERN U.S. COASTS IS INDUCING WESTERLY MID- TO UPPER-LEVEL SHEAR ON THE SYSTEM...WHILE THE SURFACE CIRCULATION IS LAGGING BEHIND IN WEAKER LOW-LEVEL FLOW AHEAD OF A COLD FRONT AND A BROAD FRONTAL LOW. HOWEVER...AS BOTH THE SHORTAVE TROUGH AND FRONTAL LOW APPROACH IRENE FROM THE WEST...THE HURRICANE IS EXPECTED TO QUICKLY ACCELERATE TO THE NORTHEAST IN RESPONSE TO THE INCREASING SOUTHWESTERLY STEERING FLOW. ONCE IRENE MOVES NORTH OF 41N LATITUDE WHERE SSTS DROP OFF SHARPLY INTO THE 14-16C RANGE...THE CYCLONE SHOULD QUICKLY DECOUPLE AND BECOME AN EXTRATROPICAL LOW. THEREAFTER...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 JUST A LITTLE TO THE RIGHT OF CONSENSUS OF THE NOW TIGHTLY PACKED NHC MODEL GUIDANCE. ALTHOUGH THE VERTICAL SHEAR IS FORECAST TO GRADUALLY INCREASE... IRENE WILL STILL BE OVER 27-28C SSTS FOR ANOTHER 24 HOURS OR SO. THIS MAY ALLOW FOR BRIEF PERIODS OF DEEP CONVECTION TO FORM NEAR THE CENTER AND KEEP THE SYSTEM GOING AS A HURRICANE. HOWEVER...ONCE IRENE MOVES NORTH OF 41N...THE MUCH COLDER WATER AND STRONG SOUTHWESTERLY SHEAR OF 30-40 KT SHOULD BRING ABOUT A QUICK DEMISE TO THIS SYSTEM AS A TROPICAL 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 STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 17/0900Z 36.6N 60.1W 75 KT 12HR VT 17/1800Z 37.7N 57.6W 65 KT 24HR VT 18/0600Z 41.0N 52.8W 60 KT 36HR VT 18/1800Z 46.7N 46.5W 50 KT...EXTRATROPICAL 48HR VT 19/0600Z 54.7N 39.2W 50 KT...EXTRATROPICAL 72HR VT 20/0600Z...ABSORBED BY EXTRATROPICAL LOW |
