000 WTPZ41 KNHC 150239 TCDEP1 TROPICAL STORM IRWIN DISCUSSION NUMBER 36 NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011 800 PM PDT FRI OCT 14 2011 THE LAST FEW VISIBLE IMAGES OF THE DAY SHOWED LOW CLOUDS IN THE SOUTHEASTERN QUADRANT OF IRWIN MOVING EASTWARD TOWARDS THE MEXICAN COAST...INSTEAD OF TURNING CYCLONICALLY AROUND THE CENTER. THIS FLOW PATTERN IS LIKELY PRODUCING LOW-LEVEL DIVERGENCE...WHICH BY ITSELF WOULD NOT BE SUPPORTIVE OF CONVECTIVE DEVELOPMENT. AS A POSSIBLE CONSEQUENCE...MUCH OF THE DEEP CONVECTION THAT DEVELOPED WITH IRWIN EARLIER IN THE DAY HAS EVAPORATED. CURRENT INTENSITY ESTIMATES FROM TAFB...SAB...AND THE UW-CIMSS ADT RANGE FROM 30 TO 50 KT...SO THE INITIAL INTENSITY IS MAINTAINED AT 40 KT. THE LOW-LEVEL CENTER BECAME A LITTLE MORE APPARENT JUST BEFORE SUNSET...AND WITH THE SUPPORT OF MICROWAVE DATA...IRWIN IS ESTIMATED TO BE MOVING SOUTH-SOUTHEASTWARD WITH A 12-HR MOTION OF 165/6 KT. A MID-LEVEL HIGH OVER NORTHWESTERN MEXICO IS EXPECTED TO EXPAND SOUTHWESTWARD OVER THE NEXT FEW DAYS AND SHOULD CAUSE IRWIN TO TURN SOUTHWARD SOON AND WESTWARD BY 48 HOURS. THEREAFTER...BROAD LOW/MID-LEVEL CYCLONIC FLOW NEAR CENTRAL AMERICA IS FORECAST TO DRIFT WESTWARD JUST FAR ENOUGH TO CAUSE IRWIN TO SLOW DOWN AND MOVE ERRATICALLY. MOST OF THE TRACK GUIDANCE AGREES ON THIS SCENARIO AND EVEN SUGGEST THAT IRWIN COULD BECOME NEARLY STATIONARY ON DAY 4 AND TURN BACK TO THE SOUTHEAST BY DAY 5. THE NEW OFFICIAL FORECAST HAS BEEN SHIFTED A LITTLE TO THE SOUTH AND WEST ON DAYS 4 AND 5 BUT IS OTHERWISE VERY SIMILAR TO THE PREVIOUS FORECAST. THE FORECAST TRACK TAKES IRWIN THROUGH A MARGINAL ENVIRONMENT FOR INTENSIFICATION DURING THE NEXT FEW DAYS. NEGATIVE FACTORS INCLUDE INCREASING VERTICAL SHEAR...THE COLD OCEANIC WAKE LEFT BY HURRICANE JOVA...A DRY ENVIRONMENTAL AIR MASS...AND THE AFOREMENTIONED LOW-LEVEL DIVERGENCE. HOWEVER AS IRWIN MOVES SOUTHWARD AWAY FROM MEXICO...IT WILL BE MOVING INTO A MOISTER AIR MASS...AND LOW-LEVEL CONVERGENCE SHOULD BE ABLE TO INCREASE. THESE FACTORS COULD FOSTER RE-DEVELOPMENT OF DEEP CONVECTION. GIVEN THE CONFLICTING SIGNALS...THE OFFICIAL FORECAST CONTINUES TO HOLD THE INTENSITY STEADY FOR THE FIRST 3 DAYS...FOLLOWED BY GRADUAL WEAKENING AND TRANSITION TO A REMNANT LOW. IT SHOULD BE NOTED THAT NEARLY ALL OF THE INTENSITY MODELS INDICATE SOME STRENGTHENING DURING THE NEXT COUPLE OF DAYS AND IS ANOTHER REASON TO NOT SHOW WEAKENING DURING THE FIRST PART OF THE FORECAST PERIOD. FORECAST POSITIONS AND MAX WINDS INIT 15/0300Z 17.7N 106.4W 40 KT 45 MPH 12H 15/1200Z 16.8N 106.7W 40 KT 45 MPH 24H 16/0000Z 15.6N 107.2W 40 KT 45 MPH 36H 16/1200Z 14.8N 108.0W 40 KT 45 MPH 48H 17/0000Z 14.5N 108.9W 40 KT 45 MPH 72H 18/0000Z 15.0N 110.0W 40 KT 45 MPH 96H 19/0000Z 15.0N 110.5W 30 KT 35 MPH 120H 20/0000Z 14.5N 110.0W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ FORECASTER BERG