000
WTPZ41 KNHC 100902
TCDEP1
 
TROPICAL STORM IRWIN DISCUSSION NUMBER  17
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP112011
200 AM PDT MON OCT 10 2011
 
CONVENTIONAL SATELLITE AND MICROWAVE IMAGERY SHOW A SIGNIFICANT LACK
OF CORE CONVECTION WITH A FRAGMENTED CURVED BANDING STRUCTURE. 
DVORAK SATELLITE ESTIMATES FROM TAFB AND SAB ARE 45 AND
35 KT RESPECTIVELY...AND THE UW-CIMSS ADVANCED DVORAK TECHNIQUE
ESTIMATE IS 40 KT.  THE INITIAL INTENSITY IS LOWERED TO 40 KT BASED
ON A BLEND OF THESE ESTIMATES.  THE SHIPS...LGEM...AND THE HURRICANE
FORECAST IMPROVEMENT PROJECT CONSENSUS MODEL ALL AGREE WITH LITTLE
CHANGE IN STRENGTH DURING THE NEXT COUPLE OF DAYS. AT DAY 4 AND
5...THE MODELS SHOW A GRADUAL WEAKENING DUE TO AN INCREASE IN
EASTERLY SHEAR.  THE INTENSITY FORECAST FOLLOWS THE MODEL GUIDANCE
CLOSELY AND NOW SHOWS SLIGHT WEAKENING AT DAY 5.

ALTHOUGH THE BEST TRACK HAS BEEN ADJUSTED A LITTLE TO THE SOUTH OF
THE PREVIOUS ADVISORY BASED ON A SERIES OF MICROWAVE IMAGES...THE
INITIAL MOTION REMAINS UNCHANGED...085/5.  AN EASTWARD OR POSSIBLY A
LITTLE SOUTH OF EASTWARD MOTION IS FORECAST DURING THE 36 HOURS AS
IRWIN TRACKS WITHIN THE FLOW TO THE EAST OF AN AMPLIFYING MID-
TO UPPER-LEVEL TROUGH TO THE SOUTHWEST OF THE BAJA PENINSULA. A TURN
EAST-NORTHEASTWARD WITH A DECREASE IN FORWARD SPEED AROUND THE 96
HR PERIOD IS EXPECTED IN THE WAKE OF HURRICANE JOVA...AND AN
INCREASING WEAKNESS IN THE SUBTROPICAL RIDGE OVER SOUTHWESTERN
MEXICO.  AT THE END OF THE FORECAST PERIOD...THE ECMWF...NOGAPS...
AND UKMET SHOW IRWIN AS A WEAK...SHALLOW CYCLONE THAT COMMENCES A
TRACK TOWARD THE SOUTHEAST WITHIN THE NORTHWESTERLY MARINE-LAYER
FLOW ALONG THE MEXICO COAST.  THE GFS...HOWEVER...IS SHOWING A
COMPLEX INTERACTION BETWEEN IRWIN...THE REMNANTS JOVA...AND A
SHORT-WAVE TROUGH TO THE NORTHWEST.  THE OFFICIAL FORECAST SIDES
WITH THE FORMER SOLUTION AND IS CLOSE TO THE MULTI-MODEL CONSENSUS
AND ALSO SHOWS A REDUCTION IN FORWARD SPEED.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  10/0900Z 14.9N 118.5W   45 KT  50 MPH
 12H  10/1800Z 15.0N 117.3W   45 KT  50 MPH
 24H  11/0600Z 15.0N 115.8W   45 KT  50 MPH
 36H  11/1800Z 14.9N 114.1W   45 KT  50 MPH
 48H  12/0600Z 15.2N 112.0W   45 KT  50 MPH
 72H  13/0600Z 16.5N 108.0W   45 KT  50 MPH
 96H  14/0600Z 17.0N 105.5W   40 KT  45 MPH
120H  15/0600Z 16.5N 104.0W   40 KT  45 MPH
 
$$
FORECASTER ROBERTS/BROWN