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| #39996 (Received by flhurricane at: 10:31 AM 16.Aug.2005) TCDAT4 HURRICANE IRENE DISCUSSION NUMBER 48 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 AM EDT TUE AUG 16 2005 IRENE IS MAINTAINING INTENSITY AT THIS TIME...AS AN EYE HAS BEEN EVIDENT ON BOTH VISIBLE AND INFRARED IMAGES. SSM/I IMAGERY ALSO SHOWS AN EYE...THAT IS CIRCULAR AND 20 N MI IN DIAMETER WITH A CLOSED WALL...ALBEIT A LITTLE WEAK OVER THE SOUTHERN SEM THE INITIAL MOTION ESTIMATE IS 090/08 BASED ON THE LAST 6 HOURS OF MICROWAVE SATELLITE POSITIONS. THE EASTWARD MOTION IS LIKELY DUE TO A SHORTWAVE CAUGHT UP IN THE FASTER WESTERLIES WELL TO THE NORTH OF IRENE THAT IS BYPASSING THE CYCLONE. THIS HAS RESULTED IN WEAKER WESTERLY STEERING FLOW ON THE SOUTH SIDE OF AN EAST-WEST ORIENTED JETSTREAM. HOWEVER...A MUCH STRONGER AND HIGHER AMPLITUDE SHORTWAVE TROUGH OVER THE EASTERN GREAT LAKES AND OHIO VALLEY REGION IS EXPECTED TO MOVE QUICKLY EASTWARD AND GRADUALLY LIFT OUT IRENE TO THE NORTHEAST BY 36 HOURS...AND THEN RAPIDLY ACCELERATE THE CYCLONE BY 48 HOURS. BETWEEN 36-48 HOURS...IRENE WILL BE MOVING OVER SUB-24C SSTS...SO TRANSITION TO A POWERFUL EXTRATROPICAL LOW PRESSURE SYSTEM IS EXPECTED. DUE TO THE MORE EASTWARD INITIAL POSITION...THE OFFICIAL FORECAST TRACK IS A LITTLE TO THE RIGHT OF THE PREVIOUS FORECAST...AND IS CLOSE TO THE NHC MODEL CONSENSUS. THE INITIAL EASTWARD MOTION WILL KEEP IRENE OVER WARMER WATER A LITTLE LONGER THAN PREVIOUSLY EXPECTED...BUT A GRADUAL INCREASE IN THE WESTERLY VERTICAL SHEAR WILL LIKELY OVERCOME ANY POSITIVE CONTRIBUTION FROM THE 28C SSTS. ONCE IRENE HITS THE ICY WATERS OF THE NORTH ATLANTIC IN ABOUT 48 HOURS...ANY REMAINING TROPICAL CHARACTERISTICS SHOULD QUICKLY DISAPPEAR. HOWEVER...WITH SUCH A STRONG SHORTWAVE TROUGH AND JETSTREAM APPROACHING...THE INCREASING BAROCLINIC ENERGY SHOULD KEEP IRENE A RATHER POTENT EXTRATROPICAL LOW PRESSURE SYSTEM OVER THE FAR NORTH ATLANTIC. ICIRCLE. DVORAK CLASSIFICATIONS GIVE A T-NUMBER OF 4.5 WHICH SUPPORTS A CURRENT INTENSITY OF 75 KT. EVEN THOUGH THE HURRICANE LOOKS QUITE HEALTHY AT THE MOMENT...ONLY A SMALL NORTHWARD COMPONENT OF MOTION WILL BRING THE SYSTEM INTO AN ENVIRONMENT OF MUCH HIGHER SHEAR...GREATER THAN 30 KNOTS. THE OFFICIAL INTENSITY FORECAST...LIKE THE PREVIOUS ONE...SHOWS A WEAKENING TREND COMMENCING WITHIN 12-24 HOURS AND THEN WEAKENS IRENE AT A SLIGHTLY FASTER RATE THAN PREDICTED BY THE SHIPS GUIDANCE. GLOBAL MODELS INDICATE THAT IRENE WILL BEGIN TO INTERACT WITH A BAROCLINIC ZONE IN ABOUT 36 HOURS. AFTER EXTRACURRICULAR TRANSITION...THE SYSTEM WILL LIKELY MERGE WITH OR BECOME ABSORBED BY ANOTHER EXTRATROPICAL CYCLONE NEAR SOUTHERN GREENLAND. INITIAL MOTION IS ESTIMATED TO BE 080/9. THE HURRICANE HAS MOVED ON A MORE EASTERLY TRACK THAN ANTICIPATED...IN PART DUE TO A LACK OF MID-LEVEL RIDGING TO ITS SOUTHEAST...RESULTING IN A MORE ZONAL STEERING CURRENT THAN EXPECTED. HOWEVER AS A 500 MB TROUGH MOVES INTO THE CANADIAN MARITIME DURING THE NEXT DAY OR SO...A GRADUAL TURN TO THE LEFT...AHEAD OF THIS TROUGH...IS ANTICIPATED. THE OFFICIAL TRACK FORECAST IS IN GOOD AGREEMENT WITH THE LATEST GFS...WHICH APPEARS TO HAVE A GOOD INITIALIZATION OF THE TROPICAL CYCLONE. FORECASTER PASCH FORECAST POSITIONS AND MAX WINDS INITIAL 16/1500Z 36.7N 62.4W 75 KT 12HR VT 17/0000Z 37.2N 60.9W 70 KT 24HR VT 17/1200Z 38.3N 58.8W 65 KT 36HR VT 18/0000Z 41.0N 54.5W 55 KT...BECOMING EXTRATROPICAL 48HR VT 18/1200Z 46.0N 48.0W 50 KT...EXTRATROPICAL 72HR VT 19/1200Z 55.0N 36.0W 45 KT...EXTRATROPICAL 96HR VT 20/1200Z...ABSORBED |
