000 WTNT44 KNHC 241450 TCDAT4 HURRICANE IRENE DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011 1100 AM EDT WED AUG 24 2011 IRENE HAS CONTINUED TO STRENGTHEN THIS MORNING. THE EYE HAS BECOME MORE DISTINCT IN SATELLITE IMAGERY AND IT IS SURROUNDED BY CLOUD TOPS COLDER THAN -70 DEGREES CELSIUS. BOTH AIR FORCE AND NOAA HURRICANE HUNTER AIRCRAFT HAVE BEEN INVESTIGATING IRENE THIS MORNING. THE AIR FORCE PLANE MEASURED A PEAK 700 MB FLIGHT-LEVEL WIND OF 112 KT JUST BEFORE 1200 UTC...AND THIS SUPPORTED THE UPGRADE TO A 100-KT CATEGORY THREE HURRICANE AT THAT TIME. SINCE THAT TIME THE NOAA AIRCRAFT REPORTED 115 KT AT 750 MB. THE PRESSURE HAS REMAINED AROUND 956 MB...AND THE INITIAL INTENSITY ESTIMATE REMAINS 100 KT. THE OUTFLOW HAS BECOME WELL ESTABLISHED OVER THE HURRICANE AND IRENE WILL BE MOVING OVER SEA SURFACE TEMPERATURES OF AROUND 29 DEGREES CELSIUS DURING THE NEXT 24-36 HOURS. THESE ENVIRONMENTAL FACTORS FAVOR ADDITIONAL INTENSIFICATION AND THE NEW INTENSITY FORECAST CALLS FOR IRENE TO REACH CATEGORY FOUR STRENGTH WITHIN 24 HOURS. AFTER THAT TIME...SOME FLUCTUATIONS IN WIND SPEEDS ARE LIKELY DUE TO EYEWALL REPLACEMENTS. THE UW-CIMSS OBJECTIVE SECONDARY EYEWALL FORMATION TECHNIQUE SHOWS A VERY HIGH LIKELIHOOD OF THAT OCCURRING DURING THE NEXT 48 HOURS. SOUTHWESTERLY SHEAR IS EXPECTED TO GRADUALLY INCREASE AND THE HURRICANE WILL BE MOVING OVER SIGNIFICANTLY COLDER WATERS BY 96 HOURS. THIS SHOULD RESULT IN GRADUAL WEAKENING...HOWEVER IRENE IS FORECAST TO REMAIN A LARGE AND POWERFUL HURRICANE DURING THE NEXT 5 DAYS. AIRCRAFT FIXES DURING THE PAST 12 HOURS INDICATE THAT IRENE HAS MADE THE EXPECTED TURN TOWARD THE NORTHWEST...WITH AN INITIAL MOTION OF 305/10. THERE IS NO CHANGE TO THE TRACK FORECAST REASONING AND THE MODEL GUIDANCE REMAINS IN EXCELLENT AGREEMENT FOR THE FIRST 2-3 DAYS. AFTER THAT TIME...THERE IS SOME QUESTION AS TO WHETHER OR NOT IRENE CONTINUES ON A NORTH-NORTHEAST HEADING OR TURNS BACK TOWARD THE NORTH AHEAD OF A MID-LATITUDE TROUGH APPROACHING THE GREAT LAKES REGION. THE GFDL AND HWRF MODELS REMAIN ALONG THE WEST SIDE OF THE GUIDANCE ENVELOPE AND SHOW A TRACK OVER OR VERY CLOSE TO THE MID-ATLANTIC COAST. THE UKMET AND NOGAPS ARE ALONG THE EASTERN SIDE AND KEEP THE CORE OF THE HURRICANE WELL OFFSHORE. GIVEN THE TYPICAL MODEL AND OFFICIAL TRACK ERRORS...BOTH SCENARIOS ARE VIABLE OPTIONS AT THIS TIME...AND USERS ARE ONCE AGAIN REMINDED NOT TO FOCUS ON SPECIFIC FORECAST POINTS THREE TO FIVE DAYS DOWNSTREAM. THE TVCA CONSENSUS AND THE EXPERIMENTAL HURRICANE FORECAST IMPROVEMENT PROJECT CONSENSUS WERE RELATIVELY CLOSE TO THE PREVIOUS NHC FORECAST. THE UPDATED NHC TRACK HAS BEEN NUDGED EASTWARD AT 96 AND 120 HOURS AND LIES BETWEEN THOSE TWO CONSENSUS AIDS. FORECAST POSITIONS AND MAX WINDS INIT 24/1500Z 22.4N 73.9W 100 KT 115 MPH 12H 25/0000Z 23.4N 74.8W 110 KT 125 MPH 24H 25/1200Z 25.1N 76.1W 115 KT 135 MPH 36H 26/0000Z 27.2N 76.9W 115 KT 135 MPH 48H 26/1200Z 29.3N 77.2W 110 KT 125 MPH 72H 27/1200Z 33.2N 76.2W 100 KT 115 MPH 96H 28/1200Z 38.5N 73.5W 85 KT 100 MPH 120H 29/1200Z 45.0N 69.5W 70 KT 80 MPH...INLAND $$ FORECASTER BROWN