000 WTNT44 KNHC 230838 TCDAT4 HURRICANE IRENE DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011 500 AM EDT TUE AUG 23 2011 SMOOTHING THROUGH ALL OF THE AIRCRAFT FIXES SINCE IRENE MOVED OFF THE COAST OF PUERTO RICO MORE THAN 18 HOURS AGO YIELDS A LONG TERM MOTION OF 295/10 KT...WHICH IS USED FOR THIS ADVISORY. THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK REASONING. THE 23/00Z G-IV JET AIRCRAFT AND AIR FORCE C-130 DROPSONDE DATA APPEAR TO HAVE SETTLED DOWN THE MODELS...AND THERE IS CONSIDERABLY LESS DIFFERENCE AMONG THE VARIOUS MODEL SOLUTIONS NOW. THE OVERWHELMING CONSENSUS IS THAT IRENE WILL GRADUALLY TURN NORTHWESTWARD OVER THE NEXT 2-3 DAYS AND THEN MOVE NORTHWARD THROUGH A DEVELOPING BREAK IN THE SUBTROPICAL RIDGE OVER THE SOUTHEASTERN UNITED STATES. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY AND LIES VERY CLOSE TO CONSENSUS MODELS TVCN AND TVCA. AN EARLIER RECON FLIGHT INDICATED THE PRESSURE HAD ONLY FALLEN BY 2 MB DOWN TO 978 MB...AND THE OVERALL APPEARANCE IN SATELLITE IMAGERY HAS CHANGED LITTLE SINCE THE PREVIOUS ADVISORY. AS A RESULT...THE INITIAL INTENSITY IS BEING HELD AT 85 KT...WHICH COULD BE GENEROUS. IRENE IS FORECAST TO REMAIN IN A RELATIVELY LOW VERTICAL WIND SHEAR ENVIRONMENT AND OVER SSTS NEAR 30C. THAT COMBINATION...ALONG WITH EXPANDING OUTFLOW IN ALL QUADRANTS...SHOULD ALLOW FOR IRENE TO BECOME A MAJOR HURRICANE WITHIN THE NEXT 24 HOURS ONCE THE CYCLONE CLEARS THE EFFECTS OF HISPANIOLA...AND PROBABLY MAINTAIN MAJOR HURRICANE STATUS THROUGHOUT THE REMAINDER OF THE 5-DAY FORECAST PERIOD. THE INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY AND CLOSELY FOLLOWS A BLEND OF THE HWRF AND GFDL MODEL INTENSITY FORECASTS...AND CONVERSION OF THE SURFACE PRESSURES DEPICTED IN THE GFS AND ECMWF MODELS. WIND RADII WERE EXPANDED BASED ON A BLEND OF RECON FLIGHT-LEVEL WINDS...SFMR WINDS...AND SURFACE OBSERVATIONS. IRENE IS FORECAST TO BECOME A LARGER THAN AVERAGE HURRICANE. IT IS IMPORTANT TO REMIND USERS NOT TO FOCUS ON THE EXACT FORECAST TRACK...ESPECIALLY AT DAYS 4 AND 5...SINCE THE MOST RECENT 5-YEAR AVERAGE ERRORS AT THOSE FORECAST TIMES ARE 200 AND 250 MILES... RESPECTIVELY. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 20.3N 70.1W 85 KT 100 MPH 12H 23/1800Z 20.9N 71.5W 95 KT 110 MPH 24H 24/0600Z 21.7N 73.3W 105 KT 120 MPH 36H 24/1800Z 22.9N 74.9W 110 KT 125 MPH 48H 25/0600Z 24.3N 76.2W 110 KT 125 MPH 72H 26/0600Z 28.0N 78.0W 115 KT 135 MPH 96H 27/0600Z 31.5N 78.3W 105 KT 120 MPH 120H 28/0600Z 35.0N 78.0W 100 KT 115 MPH...INLAND $$ FORECASTER STEWART