Tropical Storm IRWIN
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TROPICAL STORM IRWIN DISCUSSION NUMBER 32
NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011
800 PM PDT THU OCT 13 2011
TONIGHT WE HAVE RECEIVED UNCOMMON BUT WELCOME DATA. THERE ARE 3
DIFFERENT SHIPS LOCATED NEAR AND TO THE EAST OF IRWIN THAT REPORTED
AT THE SAME TIME...AND THEY ALL MEASURED WINDS OF TROPICAL STORM
FORCE. ALTHOUGH THE CLOUD PATTERN HAS NOT BECOME ANY BETTER
ORGANIZED AND THE DVORAK T-NUMBERS REMAIN UNCHANGED...THE INITIAL
INTENSITY HAS BEEN INCREASED TO 40 KNOTS BASED ON THESE SHIP
OBSERVATIONS. SOME MODELS SUGGEST THAT IRWIN SHOULD BEGIN TO
STRENGTHEN SLIGHTLY...BUT THERE IS AN UNFAVORABLE MID-LEVEL DRY
ENVIRONMENT SURROUNDING THE CYCLONE. THE LOW SHEAR AND THE WARM
OCEAN COULD COMPENSATE FOR THE DRY AIR...SO IRWIN IS KEPT AS A 35-
TO 40-KT TROPICAL STORM THROUGH 5 DAYS IN THIS ADVISORY.
THE CENTER HAS BEEN MEANDERING DURING THE PAST SEVERAL HOURS...AND
LITTLE MOTION IS ANTICIPATED DURING THE NEXT 12 TO 24 HOURS.
THEREAFTER...LIGHT MID-LEVEL NORTHERLY AND NORTHEASTERLY FLOW
SHOULD DEVELOP NEAR THE CYCLONE AS SUGGESTED BY GLOBAL MODELS...AND
THIS PATTERN SHOULD FORCE IRWIN ON A VERY SLOW SOUTHWARD AND
SOUTHWESTWARD TRACK THROUGH 5 DAYS. MOST OF GUIDANCE UNANIMOUSLY
FAVOR SUCH MOTION.
GIVEN THE SMALL AREA OF TROPICAL STORM FORCE WINDS...THE FACT THAT
IRWIN IS BASICALLY STATIONARY...AND THAT IT IS FORECAST TO MOVE
AWAY FROM MEXICO OVER THE NEXT COUPLE OF DAYS...TROPICAL STORM
WATCHES OR WARNINGS ARE NOT REQUIRED FOR THE COAST OF MEXICO AT
THIS TIME. HOWEVER...DATA FROM THESE SHIPS INDICATE THAT THE
TROPICAL STORM FORCE WINDS ARE NOT TOO FAR FROM THE MEXICAN COAST.
FORECAST POSITIONS AND MAX WINDS
INIT 14/0300Z 19.2N 106.6W 40 KT 45 MPH
12H 14/1200Z 19.0N 106.5W 35 KT 40 MPH
24H 15/0000Z 18.0N 106.2W 35 KT 40 MPH
36H 15/1200Z 16.8N 106.2W 35 KT 40 MPH
48H 16/0000Z 15.8N 107.0W 40 KT 45 MPH
72H 17/0000Z 15.0N 108.0W 40 KT 45 MPH
96H 18/0000Z 15.0N 109.0W 40 KT 45 MPH
120H 19/0000Z 15.0N 109.5W 40 KT 45 MPH
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FORECASTER AVILA
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