000 WTPZ41 KNHC 102032 TCDEP1 TROPICAL STORM IRWIN DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011 200 PM PDT MON OCT 10 2011 CONVECTION ASSOCIATED WITH IRWIN REMAINS LIMITED AND DISORGANIZED. THERE IS A RAGGED PATCH REMOVED FROM THE CENTER ON THE SOUTH SIDE OF THE CIRCULATION...WITH SPOTTY AND SOMEWHAT SHALLOW CONVECTION IN A NORTHERN BAND. DVORAK T-NUMBERS ARE UNCHANGED FROM 1200 UTC...SO THE INITIAL INTENSITY IS HELD AT 35 KT. AN EASTERLY SHEAR ENVIRONMENT CONTINUES TO PREVAIL OVER THE TROPICAL CYCLONE...WITH A MORE STABLE AIR MASS CONTINUING TO WRAP AROUND THE WEST SIDE OF THE CIRCULATION. WHILE THE EFFECT OF THE NEARBY STRATOCUMULUS FIELD MAY LESSEN AS IRWIN MOVES FARTHER AWAY FROM IT IN THE NEXT DAY OR TWO...THE SHIPS MODEL OUTPUT INDICATES NO RELENTING OF THE SHEAR. IN FACT...SOME INCREASE IN SHEAR IS SEEN TOWARD THE END OF THE FORECAST PERIOD...AND THERE IS SOME CHANCE THAT IRWIN COULD DEGENERATE INTO A SHALLOW CYCLONE BY THAT TIME. THE NHC INTENSITY FORECAST HAS BEEN LOWERED FROM THE PREVIOUS ONE AND CONTINUES TO SIDE WITH THE STATISTICAL-DYNAMICAL GUIDANCE. AS IS THE CASE WITH WEAK SYSTEMS...THE CENTER HAS BEEN DIFFICULT TO LOCATE. VISIBLE SATELLITE IMAGES SHED SOME LIGHT ON THE CENTER LOCATION AND SUGGEST THAT IRWIN IS MOVING 085/06. THE CYCLONE SHOULD BE CARRIED EASTWARD AND THEN NORTHEASTWARD WITH SOME INCREASE IN FORWARD SPEED DURING THE NEXT 2-3 DAYS AS IT BENDS CYCLONICALLY AROUND A MID-TROPOSPHERIC LOW CUTTING OFF SOUTHWEST OF BAJA CALIFORNIA. AFTER ABOUT 4 DAYS...IRWIN IS EXPECTED TO TURN EASTWARD AND EAST-SOUTHEASTWARD AS IT BECOMES EMBEDDED IN THE STRENGTHENING LOW-LEVEL WESTERLY FLOW ASSOCIATED WITH A NORTHWARD SHIFT OF THE PACIFIC ITCZ OVER MEXICO. ALTHOUGH GLOBAL MODELS SHOW SOME MID-LEVEL RIDGING BUILDING NORTH OF IRWIN BY THAT TIME...THE SHALLOW CYCLONE WILL PROBABLY NOT BE ABLE TO ESCAPE FROM THE LOW-LEVEL WESTERLIES. SOME LARGE DIFFERENCES ARE SEEN IN THE TRACK GUIDANCE AT DAYS 4-5...LIKELY DUE TO MODEL DIFFERENCES IN THE VORTEX DEPTH. THE NEW OFFICIAL TRACK FORECAST HAS BEEN LARGELY UNCHANGED FROM THE PREVIOUS ONE...AND IS BETWEEN THE MULTI-MODEL CONSENSUS AND THE SHALLOW BAM TRACK. FORECAST POSITIONS AND MAX WINDS INIT 10/2100Z 14.9N 116.9W 35 KT 40 MPH 12H 11/0600Z 14.9N 115.7W 30 KT 35 MPH 24H 11/1800Z 14.9N 114.1W 30 KT 35 MPH 36H 12/0600Z 15.3N 111.9W 30 KT 35 MPH 48H 12/1800Z 16.1N 109.7W 30 KT 35 MPH 72H 13/1800Z 17.3N 106.2W 30 KT 35 MPH 96H 14/1800Z 17.0N 104.0W 30 KT 35 MPH 120H 15/1800Z 16.5N 103.0W 30 KT 35 MPH $$ FORECASTER KIMBERLAIN