Tropical Storm IRWIN

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TROPICAL STORM IRWIN DISCUSSION NUMBER   8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
8 AM PDT SAT AUG 27 2005
 
A SMALL CLUSTER OF DEEP CONVECTION HAS PERSISTED JUST WEST OF THE
EXPOSED LOW-LEVEL CIRCULATION CENTER...WHICH IS JUST ENOUGH TO KEEP
IRWIN A 35-KT TROPICAL STORM. MODERATE EAST-SOUTHEASTERLY
UPPER-LEVEL SHEAR IS EXPECTED TO PERSIST FOR THE NEXT 96 HOURS...
WITH SOME RELAXATION OF THE SHEAR EXPECTED AFTER THAT. GIVEN THAT
IRWIN IS FORECAST TO REMAIN OVER 26-27C SSTS THROUGHOUT THE
FORECAST PERIOD...THERE MAY BE ENOUGH INTERMITTENT BURSTS OF DEEP
CONVECTION NEAR THE CENTER TO KEEP THIS SYSTEM GOING AS A MINIMAL
TROPICAL CYCLONE. THIS IS CONSISTENT WITH THE SHIPS MODEL...WHICH
ONLY WEAKENS IRWIN TO 25 KT IN 120 HOURS BENEATH 12 KT OF SHEAR.
 
THE INITIAL MOTION REMAINS AT 270/9. THE GENERAL MOTION SHOULD BE
WESTWARD AS IRWIN IS STEERED BY THE DEEP-LAYER EASTERLY FLOW ON THE
SOUTH SIDE OF A STRONG MID-LEVEL SUBTROPICAL RIDGE THAT EXTENDS
FROM MEXICO WESTWARD TO THE NORTH OF IRWIN. THIS MOTION IS
SUPPORTED BY THE CONSENSUS OF THE NHC MODEL GUIDANCE. HOWEVER...
IRWIN IS EXPECTED TO REMAIN OVER OR VERY NEAR SSTS WARM ENOUGH TO
SUPPORT THE OCCASIONAL DEVELOPMENT OF DEEP CONVECTION. THIS
INTERMITTENT STRENGTHENING OF THE VERTICAL CIRCULATION IN
CONJUNCTION WITH SOUTHEAST TO EAST-SOUTHEASTERLY UPPER-LEVEL SHEAR
MAY RESULT IN OCCASIONAL WOBBLES TO THE RIGHT...OR NORTH...OF THE
MEAN WESTERLY FORECAST TRACK INDICATED IN THE OFFICIAL ADVISORY.
 
FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      27/1500Z 17.4N 112.6W    35 KT
 12HR VT     28/0000Z 17.4N 114.0W    35 KT
 24HR VT     28/1200Z 17.5N 115.9W    35 KT
 36HR VT     29/0000Z 17.6N 117.7W    35 KT
 48HR VT     29/1200Z 17.7N 119.1W    35 KT
 72HR VT     30/1200Z 17.6N 122.0W    30 KT
 96HR VT     31/1200Z 17.5N 126.0W    25 KT
120HR VT     01/1200Z 17.5N 130.0W    25 KT
 
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