000 WTPZ41 KNHC 061443 TCDEP1 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