Tropical Storm IRWIN

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TROPICAL STORM IRWIN DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2 PM PDT FRI AUG 26 2005

GOES-10 VISIBLE IMAGERY OF IRWIN SHOWS NORTHEASTERLY SHEAR CONTINUES
TO IMPACT THE TROPICAL CYCLONE AS THE MAIN CONVECTION IS CONFINED
TO THE SOUTHWEST QUADRANT AND THE CENTER IS NOW PARTIALLY EXPOSED.
DVORAK ESTIMATES FROM TAFB AND SAB REMAIN AT 3.0 OR 45 KT.
SIMILARILY...THE MOST RECENT UW-CIMSS AND CSU-CIRA AMSU MICROWAVE
INTENSITY ESTIMATES ARE ALSO AROUND 45 KT. BASED ON THESE PRESENT
INTENSITY ESTIMATES...THE INITIAL OFFICIAL INTENSITY REMAINS AT 45
KT FOR THIS ADVISORY.

THE INTENSITY FORECAST KEEPS IRWIN AS A TROPICAL STORM FOR THE NEXT
SEVERAL DAYS. THE GFDL AND FSSE INTENSITY MODELS KEEP THE SYSTEM
BELOW 50 KT AND THEN WEAKEN IT TO DEPRESSION STRENGTH BEYOND 72
HRS. THE SHIPS MODEL PREDICTS IRWIN WILL REACH 50 KT IN THE 24-48
HR FORECAST PERIOD AND THEN FOLLOWS A SIMILAR TREND AS THE GFDL AND
FSSE. THE OFFICIAL INTENSITY FORECAST IS A BLEND OF THE AVAILABLE
INTENSITY GUIDANCE AND IT CAPS THE INTENSITY AT 45 KT IN THE FIRST
72 HRS AND EVENTUALLY DROPS IRWIN TO A TROPICAL DEPRESSION IN THE
LATER PERIOD. IF THE SHEAR CONTINUES TO IMPACT IRWIN OVER THE NEXT
DAY...THEN FASTER WEAKENING IS LIKELY.

THE INITIAL MOTION REMAINS 280/10. THERE IS LITTLE CHANGE IN
FORECAST TRACK FROM THE PREVIOUS. IRWIN WILL REMAIN SOUTH OF A
MID-LEVEL RIDGE AND IT WILL CONTINUE TO MOVE WESTWARD OVER THE NEXT
SEVERAL DAYS. THIS SCENARIO IS CONSISTENT WITH MOST OF THE
INDIVIDUAL MODELS AND CONSENSUS MODELS. IN THE EXTENDED RANGE...THE
FORECAST FOLLOWS THE NOGAPS AND GFS WEST-SOUTHWESTWARD TRACKS.

FORECASTER SISKO/STEWART
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/2100Z 17.7N 110.1W    45 KT
 12HR VT     27/0600Z 17.8N 111.5W    45 KT
 24HR VT     27/1800Z 17.9N 113.5W    45 KT
 36HR VT     28/0600Z 18.0N 115.4W    45 KT
 48HR VT     28/1800Z 18.0N 117.2W    45 KT
 72HR VT     29/1800Z 17.5N 121.0W    40 KT
 96HR VT     30/1800Z 17.0N 124.0W    35 KT
120HR VT     31/1800Z 16.5N 127.0W    30 KT...DISSIPATING
 
 
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