Hurricane IRENE

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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
 
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