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| #452961 (Received by flhurricane at: 4:55 PM 24.Aug.2011) TCDAT4 HURRICANE IRENE DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011 500 PM EDT WED AUG 24 2011 THE SATELLITE PRESENTATION OF THE HURRICANE HAS CONTINUED TO IMPROVE THIS AFTERNOON. A LARGE AREA OF DEEP CONVECTION WITH VERY COLD CLOUD TOPS HAS EXPANDED NEAR THE EYEWALL AND NOW SOLIDLY SURROUNDS THE EYE. BEFORE DEPARTING IRENE...THE AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT MEASURED A PEAK 700 MB FLIGHT-LEVEL WIND OF 116 KT IN THE NORTHEASTERN EYEWALL AND A DROPSONDE MEASURED A MINIMUM PRESSURE OF 954 MB. THESE DATA SUPPORT AN INITIAL INTENSITY OF 105 KT. ENVIRONMENTAL CONDITIONS ARE EXPECTED TO REMAIN FAVORABLE FOR SOME ADDITIONAL STRENGTHENING DURING THE NEXT DAY OR TWO. THE UW-CIMMS OBJECTIVE SECONDARY EYEWALL FORMATION TECHNIQUE CONTINUES TO PREDICT A HIGH CHANCE OF AN EYEWALL REPLACEMENT DURING THE NEXT DAY OR SO. IN FACT...A RECENT TRMM MICROWAVE PASS SHOWED SOME EVIDENCE OF A SECONDARY EYEWALL. THESE EYEWALL CYCLES CAN PRODUCE HARD TO PREDICT FLUCTUATIONS IN INTENSITY. FOR NOW...THE NEW INTENSITY FORECAST CALL FOR SOME ADDITIONAL STRENGTHENING FOLLOWED BY A LEVELING OFF OF THE INTENSITY. IN 3-4 DAYS....INCREASING SOUTHWESTERLY SHEAR AND COOLER SSTS SHOULD INDUCE GRADUAL WEAKENING...ALTHOUGH IRENE IS EXPECTED TO REMAIN A LARGE AND POWERFUL HURRICANE...OR EVEN GROW IN SIZE...AS IT NEARS NEW ENGLAND. THE HURRICANE HAS BEEN MOVING NORTHWESTWARD OR 310/10 KT. IRENE IS EXPECTED TO TURN TOWARD THE NORTH-NORTHWEST THEN NORTH THROUGH A BREAK IN THE SUBTROPICAL RIDGE OVER THE WESTERN ATLANTIC DURING THE NEXT COUPLE OF DAYS. AFTER THAT TIME...THE HURRICANE IS FORECAST TO TURN NORTH-NORTHEASTWARD AROUND THE NORTHWESTERN SIDE OF THE RIDGE. BETWEEN 72 AND 96 HOURS...THERE REMAINS UNCERTAINTY AS TO WHETHER IRENE TURNS BACK TOWARD THE NORTH AHEAD OF A MID-LATITUDE TROUGH MOVING INTO THE GREAT LAKES REGION AT THAT TIME. THE NEW ECMWF SHOWS MUCH MORE AMPLIFICATION OF THE TROUGH... WHICH HAS RESULTED IN ITS TRACK SHIFTING OVER 100 MILES TO THE WEST...AND THIS SKILLFUL LONG-RANGE MODEL NOW DEFINES THE WESTERN EDGE OF THE GUIDANCE ENVELOPE. OVERALL...THE GUIDANCE ENVELOPE HAS SHIFTED A LITTLE WESTWARD AT DAYS 4 AND 5. THE NEW TRACK FORECAST IS CLOSE TO THE PREVIOUS ADVISORY AND IS BETWEEN THE GFS AND ECMWF MODELS. THIS IS ALSO CLOSE TO THE TVCA AND EXPERIMENTAL HURRICANE FORECAST IMPROVEMENT PROJECT...HFIP...CONSENSUS TRACKS. FORECAST POSITIONS AND MAX WINDS INIT 24/2100Z 23.1N 74.7W 105 KT 120 MPH 12H 25/0600Z 24.3N 75.8W 110 KT 125 MPH 24H 25/1800Z 26.1N 76.8W 115 KT 135 MPH 36H 26/0600Z 28.2N 77.3W 115 KT 135 MPH 48H 26/1800Z 30.1N 77.3W 110 KT 125 MPH 72H 27/1800Z 34.3N 75.8W 100 KT 115 MPH 96H 28/1800Z 39.5N 73.0W 85 KT 100 MPH 120H 29/1800Z 47.0N 69.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ FORECASTER BROWN |
