000 WTPZ41 KNHC 142033 TCDEP1 TROPICAL STORM IRWIN DISCUSSION NUMBER 35 NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011 200 PM PDT FRI OCT 14 2011 THE CONVECTIVE ORGANIZATION OF IRWIN INCREASED AGAIN OVER THE PAST FEW HOURS...WITH TOPS COOLING NEAR THE CENTER AND THE CONVECTIVE PATTERN TAKING ON A MORE BANDED STRUCTURE. BASED ON A SHIP OBSERVATION OF 37-KT WINDS AND THE 18Z TAFB DVORAK ESTIMATE...THE INTENSITY IS RAISED TO 40 KT. IRWIN WILL BE MOVING THROUGH A MARGINAL ENVIRONMENT FOR THE NEXT SEVERAL DAYS...CHARACTERIZED BY DRY MID-LEVEL AIR...THE COOL WAKE LEFT FROM HURRICANE JOVA...AND MODERATE TO STRONG VERTICAL SHEAR. DESPITE THIS...MOST OF THE INTENSITY GUIDANCE CONTINUES TO INSIST ON GRADUAL STRENGTHENING THROUGH THE PERIOD. GIVEN THE LESS THAN IDEAL ENVIRONMENT AND THE SPORADIC NATURE OF THE CONVECTIVE ORGANIZATION DURING THE PAST COUPLE OF DAYS...THE OFFICIAL FORECAST SHOWS NO CHANGE FOR THE FIRST 72 HOURS. GRADUAL DECAY TO A REMNANT LOW BY DAY 5 IS EXPECTED AS THE SHEAR INCREASES FURTHER AND THE GLOBAL MODELS SHOW THE VORTEX WEAKENING OR DISSIPATING BY THAT TIME. THE INITIAL MOTION ESTIMATE IS 180/4...AS IRWIN IS LOCATED TO THE SOUTH OF A MID-LEVEL RIDGE BUILDING SOUTHEASTWARD OVER BAJA CALIFORNIA AND WESTERN MEXICO. THE CYCLONE WILL GRADUALLY TURN TOWARD THE WEST OVER THE NEXT COUPLE OF DAYS AS THE RIDGE TO THE NORTH BUILDS WESTWARD AND TAKES ON A MORE EAST/WEST ORIENTATION...AND THE TRACK GUIDANCE IS IN GOOD AGREEMENT ON THIS SCENARIO. AFTER THAT TIME THE RIDGE BREAKS DOWN...WHICH SHOULD RESULT IN A SLOW AND/OR ERRATIC MOTION...AS INDICATED BY THE LARGE SPREAD IN THE GUIDANCE AT THAT TIME. THE NEW NHC TRACK FORECAST IS TRENDED TOWARD THE NEW MULTI-MODEL CONSENSUS...AND IS A LITTLE FASTER AND A BIT TO THE RIGHT OF THE PREVIOUS ONE THROUGH 36 HOURS. AFTER THAT TIME THE NHC TRACK IS ESSENTIALLY AN UPDATE OF THE PREVIOUS ONE...SHOWING LITTLE OR NO MOTION AT DAYS 3 THROUGH 5 DUE TO THE LARGE UNCERTAINTY AT THIS TIME RANGE. FORECAST POSITIONS AND MAX WINDS INIT 14/2100Z 18.0N 106.9W 40 KT 45 MPH 12H 15/0600Z 17.2N 107.1W 40 KT 45 MPH 24H 15/1800Z 16.0N 107.4W 40 KT 45 MPH 36H 16/0600Z 15.1N 107.9W 40 KT 45 MPH 48H 16/1800Z 14.7N 108.9W 40 KT 45 MPH 72H 17/1800Z 15.0N 109.8W 35 KT 40 MPH 96H 18/1800Z 15.0N 110.0W 30 KT 35 MPH 120H 19/1800Z 15.0N 110.0W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ FORECASTER BRENNAN