Tropical Storm IRWIN
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TROPICAL STORM IRWIN DISCUSSION NUMBER 18
NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011
800 AM PDT MON OCT 10 2011
SIMILAR TO WHAT OCCURRED YESTERDAY...IRWIN HAS LOST MOST OF ITS DEEP
CONVECTION. ALL THAT REMAINS IS A PATCH OF MEAGER CONVECTION THAT
HAS RECENTLY FORMED SOUTH OF THE CIRCULATION CENTER. DVORAK
T-NUMBERS HAVE DECREASED ACCORDINGLY...AND A BLEND OF THE LATEST T-
AND CI-NUMBERS ARE USED TO SET THE INITIAL INTENSITY ESTIMATE AT 35
KT. IRWIN APPEARS TO BE PULLING IN RELATIVELY COOLER AND MORE
STABLE AIR FROM THE WEST...AS EVIDENCED BY THE SOUTHWARD
DISPLACEMENT OF THE NEARBY STRATOCUMULUS FIELD. THIS COULD
TEMPORARILY BE LIMITING ANY RE-DEVELOPMENT OF SIGNIFICANT DEEP
CONVECTION AND HENCE INTENSIFICATION. EASTERLY SHEAR IS ANOTHER
LIMITING FACTOR AND IS FORECAST BY THE DYNAMICAL MODELS TO PERSIST
AT ROUGHLY THE SAME MAGNITUDE FOR THE NEXT 3-4 DAYS AND POSSIBLY
EVEN INCREASE AT THE END OF THE FORECAST PERIOD. WHILE THE
DYNAMICAL GUIDANCE SHOWS SOME STRENGTHENING...THE OBJECTIVE
STATISTICAL OUTPUT CONTINUES TO SHOW A SLOW DECAY. THE OFFICIAL
INTENSITY FORECAST IS REDUCED A BIT FROM THE PREVIOUS ONE TO
ACCOUNT FOR THE RECENT WEAKENING. IT ALSO LEANS TOWARD A BLEND OF
SHIPS/LGEM AND THE INTENSITY CONSENSUS AIDS...GIVEN HOW MUCH THE
SYSTEM IS CURRENTLY STRUGGLING.
RECENT CENTER FIXES REMAIN UNCERTAIN...AND THE INITIAL MOTION
ESTIMATE APPEARS TO BE 085/06. IRWIN IS EXPECTED TO BE CARRIED ON
AN ATYPICAL EASTWARD AND THE NORTHEASTWARD TRACK FOR THE NEXT
SEVERAL DAYS AS IT BENDS CYCLONICALLY AROUND A CUT-OFF LOW
DEVELOPING SOUTHWEST OF BAJA CALIFORNIA. BY ABOUT 96 HOURS...
IRWIN...PERHAPS AS A SHALLOW CYCLONE...IS LIKELY TO BE PULLED BACK
TOWARD THE EAST AND EVEN SOUTHEAST INTO A BROAD LOW- TO MID-LEVEL
CYCLONIC GYRE OVER MEXICO. THE MODEL GUIDANCE IS IN GOOD AGREEMENT
ON THIS SCENARIO...AND THE CURRENT FORECAST IS ESSENTIALLY AN
UPDATE OF THE PREVIOUS ONE.
FORECAST POSITIONS AND MAX WINDS
INIT 10/1500Z 15.0N 117.7W 35 KT 40 MPH
12H 11/0000Z 15.1N 116.4W 35 KT 40 MPH
24H 11/1200Z 15.0N 114.8W 40 KT 45 MPH
36H 12/0000Z 15.1N 112.9W 40 KT 45 MPH
48H 12/1200Z 15.6N 110.9W 40 KT 45 MPH
72H 13/1200Z 16.9N 107.4W 40 KT 45 MPH
96H 14/1200Z 17.1N 105.1W 40 KT 45 MPH
120H 15/1200Z 16.4N 103.9W 35 KT 40 MPH
$$
FORECASTER KIMBERLAIN
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