309 
 WTPZ41 KNHC 080245
 TCDEP1
  
 HURRICANE IRWIN DISCUSSION NUMBER   8
 NWS NATIONAL HURRICANE CENTER MIAMI FL       EP112011
 800 PM PDT FRI OCT 07 2011
 
 IRWIN HAS A WELL-DEFINED CENTRAL DENSE OVERCAST THIS EVENING...WITH
 CLOUD TOPS COLDER THAN -80C TO THE SOUTHEAST OF THE CENTER. WHILE
 THE EYE SEEN EARLIER IN SATELLITE IMAGES IS NOT CURRENTLY
 APPARENT...EARLIER MICROWAVE IMAGES SUGGEST IT IS STILL PRESENT
 UNDER THE OVERCAST. THE SATELLITE INTENSITY ESTIMATES FROM TAFB AND
 SAB HAVE NOT CHANGED...SO THE INITIAL INTENSITY REMAINS 80 KT.
 ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN SHOW ABOUT 15 KT
 OF EASTERLY VERTICAL WIND SHEAR OVER IRWIN...AND THIS IS CAUSING
 THE OUTFLOW TO THE EAST TO BE RESTRICTED.
 
 IRWIN CONTINUES TO SLIDE FARTHER WEST-NORTHWESTWARD THAN FORECAST...
 WITH THE INITIAL MOTION 295/4. THE TRACK GUIDANCE IS IN GOOD
 AGREEMENT THAT THE FORWARD MOTION SHOULD COME TO A HALT LATER
 TONIGHT AS A LARGE MID/UPPER-LEVEL TROUGH TO THE NORTH INCREASES
 ITS INFLUENCE ON IRWIN. THIS TROUGH IS FORECAST TO CAUSE THE
 HURRICANE TO TURN TOWARD THE EAST-NORTHEAST BY 36 HOURS...AND
 TOWARD THE EAST AFTER 36 HOURS. THE TRACK GUIDANCE IS IN GOOD
 AGREEMENT ON THE DIRECTION OF MOTION...BUT THERE IS SOME SPREAD IN
 THE FORWARD SPEED BETWEEN THE FASTER ECMWF AND THE SLOWER
 GFS/NOGAPS MODELS. OVERALL...THE NEW GUIDANCE IS A LITTLE SLOWER
 THAN EARLIER...AND THUS THE NEW FORECAST TRACK IS A LITTLE SLOWER
 THAN THE PREVIOUS TRACK. THE NEW TRACK LIES NEAR THE CENTER OF THE
 TRACK GUIDANCE ENVELOPE.
 
 THE DYNAMICAL MODELS FORECAST IRWIN TO ENCOUNTER INCREASED SHEAR AS
 IT MAKES ITS EASTWARD TURN IN 24-36 HOURS.  THE INTENSITY FORECAST
 SHOWS SOME SLOW STRENGTHENING BEFORE THAT TIME...AND SLOW WEAKENING
 AFTER THAT TIME.  THE NEW INTENSITY FORECAST IS SIMILAR TO THE
 SHIPS AND LGEM MODELS FOR THE FIRST 36 HOURS...AND A LITTLE
 STRONGER THAN THOSE MODELS AFTER THAT TIME.  AS MENTIONED IN THE
 PREVIOUS DISCUSSION...THERE IS A POSSIBILITY THAT CONDITIONS COULD
 BECOME MORE FAVORABLE FOR STRENGTHENING AT ABOUT 120 HOURS. 
 HOWEVER...THE EVIDENCE OF THAT OCCURRING NEEDS TO BE STRONGER
 BEFORE THE FORECAST CAN SHOW STRENGTHENING AT THAT TIME.
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  08/0300Z 14.1N 121.3W   80 KT  90 MPH
  12H  08/1200Z 14.4N 121.4W   80 KT  90 MPH
  24H  09/0000Z 14.7N 121.1W   85 KT 100 MPH
  36H  09/1200Z 14.9N 120.5W   85 KT 100 MPH
  48H  10/0000Z 15.0N 119.5W   80 KT  90 MPH
  72H  11/0000Z 15.0N 117.0W   70 KT  80 MPH
  96H  12/0000Z 15.0N 113.5W   65 KT  75 MPH
 120H  13/0000Z 16.5N 109.0W   60 KT  70 MPH
  
 $$
 FORECASTER BEVEN