Hurricane IRENE

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HURRICANE IRENE DISCUSSION NUMBER  32
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 AM EDT SUN AUG 28 2011
 
SATELLITE AND RADAR IMAGERY SHOW THAT DRY AIR IS NOW WRAPPING INTO
MUCH OF THE SOUTHERN SEMICIRCLE OF IRENE...AND THE CYCLONE IS
SLOWLY BEGINNING TO FILL AS MEASUREMENTS FROM THE AIR FORCE RESERVE
HURRICANE HUNTER AIRCRAFT SHOW THAT THE CENTRAL PRESSURE IS UP TO
958 MB.  BASED ON DROPSONDE AND SFMR DATA SHOWING THAT SURFACE
WINDS HAVE CONTINUED TO SLOWLY WEAKEN...THE INITIAL INTENSITY IS
LOWERED TO 65 KT FOR THIS ADVISORY.  DESPITE THE GRADUAL WEAKENING
OF THE CYCLONE...THE OUTER WIND FIELD CONTINUES TO EXPAND...WITH
34-KT WINDS OCCURRING FROM NEW YORK CITY SOUTHWARD TO NORTHEASTERN
NORTH CAROLINA.  IRENE IS EXPECTED TO REMAIN NEAR HURRICANE
STRENGTH UNTIL IT MOVES INTO SOUTHERN NEW ENGLAND LATER TODAY...
AND IT WILL ONLY TAKE MODEST CONVECTION TO BRING DOWN STRONGER WINDS
ALOFT TO THE SURFACE AS SUSTAINED HURRICANE-FORCE WINDS OR GUSTS. 
SLOW WEAKENING IS EXPECTED AFTER LANDFALL AS IRENE BECOMES A
POST-TROPICAL CYCLONE IN ABOUT 24 HOURS.
 
THE INITIAL MOTION ESTIMATE IS 020/16...AS IRENE CONTINUES TO
ACCELERATE TOWARD THE NORTH-NORTHEAST ON THE WESTERN SIDE OF THE
SUBTROPICAL RIDGE.  OVER THE NEXT DAY OR SO...IRENE WILL MERGE INTO
THE MID-LATITUDE WESTERLIES AND ACCELERATE NORTHEASTWARD OVER
EASTERN CANADA AND INTO THE NORTH ATLANTIC.  THE TRACK GUIDANCE
REMAINS TIGHTLY PACKED...BUT HAS SHIFTED A LITTLE TO THE LEFT IN
THE VERY SHORT TERM.  THE NEW NHC TRACK FORECAST HAS BEEN ADJUSTED
IN THAT DIRECTION AND IS CLOSE TO THE ECMWF THROUGH 24 HOURS. 
AFTER EXTRATROPICAL TRANSITION THE NHC FORECAST IS A BLEND OF THE
GFS...ECMWF...AND UKMET.
 
NOTE...MORE SO THAN WITH MOST STORMS...THE WINDS WITH IRENE INCREASE
SHARPLY WITH HEIGHT ABOVE THE SURFACE.  AS IRENE MOVES THROUGH
AREAS WITH HIGH-RISE STRUCTURES...THESE BUILDINGS COULD EXPERIENCE
WINDS SIGNIFICANTLY STRONGER THAN THE SURFACE WINDS.  WINDS AT THE
30-STORY LEVEL WILL LIKELY BE 20 PERCENT HIGHER THAN AT THE
SURFACE...AND WINDS 80-100 STORIES UP COULD BE ABOUT 30 PERCENT
HIGHER THAN AT THE SURFACE.

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  28/0900Z 39.2N  74.5W   65 KT  75 MPH
 12H  28/1800Z 41.8N  73.2W   60 KT  70 MPH...INLAND
 24H  29/0600Z 46.0N  70.4W   55 KT  65 MPH...POST-TROP/EXTRATROP
 36H  29/1800Z 50.6N  66.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
 48H  30/0600Z 54.0N  59.5W   40 KT  45 MPH...POST-TROP/EXTRATROP
 72H  31/0600Z 58.0N  44.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  01/0600Z 61.0N  31.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  02/0600Z 62.0N  28.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BRENNAN
 
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