753 
 WTPZ41 KNHC 080854
 TCDEP1
  
 HURRICANE IRWIN DISCUSSION NUMBER   9
 NWS NATIONAL HURRICANE CENTER MIAMI FL       EP112011
 200 AM PDT SAT OCT 08 2011
  
 IT APPEARS THAT THERE IS A LITTLE BIT OF EASTERLY SHEAR AFFECTING
 IRWIN...AND THE LOW-LEVEL CENTER MAY NOW BE LOCATED CLOSER TO THE
 EASTERN EDGE OF THE CENTRAL DENSE OVERCAST.  SUBJECTIVE AND
 OBJECTIVE DVORAK CURRENT INTENSITY ESTIMATES RANGE FROM 77 KT TO 90
 KT...AND THE INTENSITY IS BEING KEPT AT 80 KT SINCE THERE HAS NOT
 BEEN AN INCREASE IN ORGANIZATION SINCE THE LAST ADVISORY.
 
 IRWIN IS MOVING SLOWLY NORTHWESTWARD...OR 315 DEGREES AT 4 KT.  THE
 CYCLONE IS TRAPPED WITHIN A WEAK STEERING REGIME BETWEEN TROPICAL
 STORM JOVA TO ITS EAST...A LARGE SUBTROPICAL RIDGE TO ITS
 NORTHWEST...AND A MID-LATITUDE TROUGH TO THE NORTHEAST.  THIS WEAK
 STEERING IS EXPECTED TO CONTINUE FOR ANOTHER 36 TO 48 HOURS UNTIL A
 MID-LATITUDE SHORTWAVE TROUGH DIGS SOUTHWARD OFF THE BAJA
 CALIFORNIA COAST.  IRWIN SHOULD THEN ACCELERATE TOWARD THE
 EAST-NORTHEAST FROM 48 TO 96 HOURS.  THE GLOBAL MODELS ARE
 SUGGESTING THAT THE SHORTWAVE TROUGH WILL CUTOFF IN 3 TO 4
 DAYS...AND THIS WOULD LIKELY CAUSE IRWIN TO BEGIN TURNING
 NORTHEASTWARD AROUND THE SOUTHEASTERN SIDE OF THE CUT-OFF LOW BY
 DAY 5.  THE TRACK GUIDANCE IS IN GOOD AGREEMENT ON THIS
 SCENARIO...AND ONLY A SLIGHT NORTHWARD SHIFT FROM THE PREVIOUS
 FORECAST WAS REQUIRED ON DAY 5.
 
 THE SHIPS DIAGNOSTICS ARE INDICATING THAT THE ENVIRONMENT IN THE
 VICINITY OF IRWIN MAY BE TOO STABLE AND TOO WARM IN THE UPPER
 LEVELS OF THE ATMOSPHERE TO SUPPORT SIGNIFICANT INTENSIFICATION. 
 THEREFORE...LITTLE CHANGE IN INTENSITY IS INDICATED IN THE OFFICIAL
 FORECAST THROUGH 36 HOURS.  GRADUAL WEAKENING IS FORECAST TO
 COMMENCE AFTER 36 HOURS DUE TO THE AFOREMENTIONED ENVIRONMENTAL
 CONDITIONS...DECREASING SEA SURFACE TEMPERATURES...AND INCREASING
 VERTICAL SHEAR ON DAYS 3 AND 4 ONCE THE SHORTWAVE TROUGH CUTS OFF. 
 THIS FORECAST IS CLOSER TO THE STATISTICAL GUIDANCE THAN THE MORE
 AGGRESSIVE GFDL AND HWRF MODELS. 
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  08/0900Z 14.4N 121.1W   80 KT  90 MPH
  12H  08/1800Z 14.8N 120.9W   80 KT  90 MPH
  24H  09/0600Z 15.1N 120.5W   80 KT  90 MPH
  36H  09/1800Z 15.3N 119.8W   80 KT  90 MPH
  48H  10/0600Z 15.4N 118.7W   75 KT  85 MPH
  72H  11/0600Z 15.5N 116.0W   70 KT  80 MPH
  96H  12/0600Z 16.0N 112.0W   65 KT  75 MPH
 120H  13/0600Z 18.5N 108.0W   60 KT  70 MPH
  
 $$
 FORECASTER BERG