Tropical Storm IRWIN

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TROPICAL STORM IRWIN DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP112011
800 AM PDT THU OCT 06 2011

THE CLOUD PATTERN OF THE TROPICAL CYCLONE HAS GRADUALLY BECOME
BETTER ORGANIZED THIS MORNING...WITH A CURVED CONVECTIVE BAND
WRAPPING ABOUT HALFWAY AROUND THE ESTIMATED CENTER.  DVORAK
T-NUMBERS FROM TAFB AND SAB ARE NOW 2.5...CORRESPONDING TO AN
INTENSITY OF 35 KT...AND THE SYSTEM IS BEING NAMED AT THIS TIME. 
UPPER-LEVEL OUTFLOW IS WELL DEFINED OVER THE WESTERN SEMICIRCLE AND
RESTRICTED TO THE EAST.  SOUTHEASTERLY TO SOUTHERLY SHEAR IS
FORECAST TO INCREASE OVER IRWIN OVER THE NEXT FEW DAYS...PARTIALLY
DUE TO THE INFLUENCE OF ANOTHER TROPICAL CYCLONE NOT FAR TO THE
EAST.  SLOW STRENGTHENING IS PREDICTED...FOLLOWING THE
STATISTICAL-DYNAMICAL GUIDANCE. 

LATEST CENTER FIXES REQUIRE A SLIGHT RELOCATION TO THE EAST OF THE
PREVIOUS TRACK.  THE STORM HAS BEEN MOVING SLOWLY
WEST-NORTHWESTWARD...ON THE SOUTHWEST SIDE OF A WEAK MID-LEVEL
RIDGE.  OVER THE NEXT COUPLE OF DAYS A LARGE MID-TROPOSPHERIC
TROUGH IS FORECAST TO AMPLIFY TO THE NORTH OF IRWIN.  THIS CHANGE
IN THE STEERING PATTERN SHOULD CAUSE THE TROPICAL CYCLONE TO TURN
NORTHWARD AND EVENTUALLY EAST-NORTHEASTWARD DURING THE FORECAST
PERIOD.  SINCE ANOTHER TROPICAL CYCLONE WILL BE SITUATED 7 TO 10
DEGREES TO THE EAST...SOME INTERACTION BETWEEN THESE TWO SYSTEMS IS
PROBABLE.  AT THIS TIME THE MOST LIKELY SCENARIO IS FOR IRWIN TO
TRAIL THE NEIGHBORING CYCLONE AS THE LATTER SYSTEM MOVES TOWARD THE
MEXICAN COAST.  IT IS CERTAINLY POSSIBLE HOWEVER THAT THE TWO
CYCLONES WILL MOVE MORE IN TANDEM TOWARD THE COAST...AS SUGGESTED
BY RECENT GFS MODEL RUNS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  06/1500Z 12.4N 116.8W   35 KT  40 MPH
 12H  07/0000Z 12.7N 117.5W   35 KT  40 MPH
 24H  07/1200Z 13.0N 117.7W   40 KT  45 MPH
 36H  08/0000Z 13.5N 117.5W   45 KT  50 MPH
 48H  08/1200Z 13.8N 117.4W   50 KT  60 MPH
 72H  09/1200Z 14.0N 117.0W   50 KT  60 MPH
 96H  10/1200Z 14.5N 116.0W   50 KT  60 MPH
120H  11/1200Z 15.5N 113.0W   50 KT  60 MPH
 
$$
FORECASTER PASCH
 
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