918 
 WTNT44 KNHC 220859
 TCDAT4
  
 HURRICANE IRENE DISCUSSION NUMBER   7
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
 500 AM AST MON AUG 22 2011
  
 IRENE HAS BECOME MUCH BETTER ORGANIZED DURING THE PAST 6 HOURS
 DESPITE ITS INTERACTION WITH THE MOUNTAINOUS TERRAIN OF PUERTO
 RICO...AND A RAGGED EYE HAS BECOME APPARENT IN IMAGERY FROM THE FAA
 TERMINAL DOPPLER WEATHER RADAR. ALSO...LARGE PATCHES OF DOPPLER
 VELOCITY VALUES AS HIGH AS 75-82 KT AT 1000-1500 FT AND 85-91 KT 
 AT 2000-3000 FT HAVE BEEN INDICATED NORTHWEST AND NORTHEAST OF THE
 CENTER OVER WATER FOR THE PAST 2 HOURS...WHICH EQUATES TO AT LEAST
 65-KT SURFACE WINDS. SOME DOPPLER VELOCITIES AS HIGH AS 72 KT HAVE
 ALSO BEEN DETECTED AT 500-600 FT OVER WATER. AS A RESULT OF THESE
 DATA...IRENE HAS BEEN UPGRADED TO THE FIRST HURRICANE OF THE 2011
 ATLANTIC HURRICANE SEASON.
 
 TRENDING THROUGH ALL OF THE WOBBLES IN THE TRACK OVER THE PAST 6
 HOURS YIELDS AN AVERAGE MOTION OF ABOUT 290/10 KT. UPPER-AIR DATA
 AT 00Z INDICATE 500 MB HEIGHTS HAVE NOT CHANGED AT BERMUDA IN THE
 PAST 24 HOURS...WHICH SUGGESTS THAT THE SUBTROPICAL RIDGE TO THE
 NORTH OF IRENE REMAINS QUITE STRONG. THE RIDGE IS EXPECTED TO
 CHANGE LITTLE FOR THE NEXT 48 HOURS OR SO...WHICH WOULD ACT TO KEEP
 IRENE MOVING IN A GENERAL WEST-NORTHWESTWARD DIRECTION OFF THE
 NORTH COAST OF PUERTO RICO THIS MORNING AND JUST SKIRTING THE
 NORTHERN COAST OF HISPANIOLA LATER TODAY AND ON TUESDAY. AFTER
 THAT...THE GLOBAL MODELS DIVERGE ON THE SPECIFICS OF HOW LARGE A
 BREAK OR WEAKNESS IN THE SUBTROPICAL RIDGE DEVELOPS OVER FLORIDA
 AND THE SOUTHEASTERN U.S. AT 72 HOUR AND BEYOND...WHICH WILL ALLOW
 IRENE TO MOVE NORTHWESTWARD. THE ECMWF...NOGAPS...AND GFDN MODELS
 ARE THE RIGHTMOST OF THE NHC MODEL GUIDANCE SUITE AND KEEP IRENE
 WELL EAST OF FLORIDA...WHEREAS THE UKMET AND THE GFDL MODELS ARE
 THE LEFTMOST OF THE MODELS AND TAKE IRENE NEAR THE WEST COAST OF
 FLORIDA. THE GFS AND THE REST OF THE NHC MODEL GUIDANCE IS TIGHTLY
 PACKED BETWEEN THESE TWO EXTREMES AND TAKE IRENE THROUGH THE
 BAHAMAS AND JUST OFF THE FLORIDA EAST COAST. WHAT IS NOTEWORTHY IS
 THAT ALL OF THE GLOBAL AND REGIONAL MODELS AGREE THAT THE OUTFLOW
 OF IRENE WILL CONVERGE WITH WESTERLY TO NORTHWESTERLY UPPER-LEVEL
 MID-LATITUDE FLOW OVER THE MID-ATLANTIC STATES BY 96 HOURS AND
 BEYOND. THIS UPPER-LEVEL MASS CONFLUENCE COULD MAINTAIN THE MID- TO
 LOW-LEVEL RIDGE A LITTLE BIT STRONGER AND LONGER THAN WHAT NOGAPS
 AND THE ECMWF ARE FORECASTING...WHICH WOULD IN TURN KEEP IRENE A
 LITTLE CLOSER TO THE FLORIDA EAST COAST. AS A RESULT...THE OFFICIAL
 FORECAST TRACK WAS ONLY SHIFTED SLIGHTLY TO THE EAST OF THE
 PREVIOUS TRACK AND IS NEAR THE CONSENSUS MODELS TVCN AND TVCA.
 
 IT NOW APPEARS THAT IRENE WILL NOT INTERACT WITH HISPANIOLA AS MUCH
 OR AS LONG AS PREVIOUSLY EXPECTED. THIS WILL ALSO RESULT IN MORE
 STRENGTHENING THAN PREVIOUSLY EXPECTED. IRENE IS FORECAST BY ALL OF
 THE MODELS TO HAVE A VERY IMPRESSIVE OUTFLOW PATTERN THROUGHOUT THE
 FORECAST PERIOD...INCLUDING A LARGE UPPER-LEVEL TROUGH/LOW ABOUT
 1200 NMI EAST OF THE CYCLONE ACTING AS A MASS SINK. WITH IRENE ALSO
 EXPECTED TO BE OVER SSTS NEAR 30C AFTER 48 HOURS...SIGNIFICANT
 STRENGTHENING COULD OCCUR. HOWEVER...THE OFFICIAL INTENSITY WILL
 REMAIN ON THE CONSERVATIVE SIDE DUE TO THE UNCERTAINTY IN HOW MUCH
 IRENE WILL INTERACT WITH THE MOUNTAINOUS TERRAIN OF HISPANIOLA FOR
 THE NEXT 24-36 HOURS. THE OFFICIAL INTENSITY FORECAST IS A BLEND OF
 THE SHIPS/LGEM MODELS AND THE HWRF/GFDL MODELS. HOWEVER...GIVEN THE
 IMPRESSIVE UPPER-LEVEL FLOW PATTERN EXPECTED ACROSS IRENE...IT
 WOULD NOT SURPRISE ME IF THIS CYCLONE BECAME A MAJOR HURRICANE AT
 SOME TIME DURING ITS LIFETIME LIKE THE GFDL AND HWRF MODELS ARE
 FORECASTING.
 
 IT IS IMPORTANT NOT TO FOCUS ON THE EXACT FORECAST TRACK...
 ESPECIALLY AT DAYS 4 TO 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  22/0900Z 18.4N  66.4W   65 KT  75 MPH
  12H  22/1800Z 18.9N  68.2W   70 KT  80 MPH
  24H  23/0600Z 19.7N  70.5W   70 KT  80 MPH...INLAND
  36H  23/1800Z 20.4N  72.4W   70 KT  80 MPH...OVER WATER
  48H  24/0600Z 21.3N  74.1W   75 KT  85 MPH
  72H  25/0600Z 24.0N  77.1W   80 KT  90 MPH
  96H  26/0600Z 27.0N  79.5W   85 KT 100 MPH
 120H  27/0600Z 30.9N  81.5W   95 KT 110 MPH
  
 $$
 FORECASTER STEWART