000 WTPZ41 KNHC 150836 TCDEP1 TROPICAL STORM IRWIN DISCUSSION NUMBER 37 NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011 200 AM PDT SAT OCT 15 2011 CONVECTION HAS REDEVELOPED IN THE SOUTHEASTERN QUADRANT OF THE STORM DURING THE PAST FEW HOURS. HOWEVER THIS CONVECTION IS NOT AS EXTENSIVE OR ORGANIZED AS YESTERDAY...AND DVORAK ESTIMATES ARE DECREASING. THE INITIAL WIND SPEED IS SET TO 35 KT WHICH MATCHES THE CI NUMBERS FROM TAFB/SAB. WATER VAPOR IMAGES SHOW DRY AIR ALOFT POURING INTO THE CIRCULATION OF IRWIN...SO THE RECENT CONVECTIVE BURST WILL PROBABLY BE SHORT-LIVED. THIS DRY AIR...COMBINED WITH THE CYCLONE SOON MOVING OVER THE COLD WAKE OF JOVA AND AN INCREASE IN NORTHEASTERLY SHEAR... SHOULD CAUSE THE SYSTEM TO WEAKEN INTO A TROPICAL DEPRESSION LATER TODAY. ALMOST ALL OF THE GUIDANCE BESIDES THE GFS NOW SHOW THIS SOLUTION...SO THE OFFICIAL FORECAST IS LOWERED FROM THE PREVIOUS ONE. SOME OF THE GUIDANCE STILL SHOW SOME RESTRENGTHENING IN A COUPLE OF DAYS...BUT THIS SEEMS UNLIKELY DUE TO THE FORECAST TRACK MOVING RIGHT OVER THE WATERS UPWELLED FROM JOVA AND NORTHEASTERLY SHEAR ONLY LIKELY TO GET STRONGER. IRWIN IS FORECAST TO BECOME A REMNANT LOW BY DAY 3...AND I WOULD NOT BE SURPRISED IF IT HAPPENED SOONER. ALTHOUGH THE CENTER HAS BEEN A BIT DIFFICULT TO LOCATE...THE CYCLONE APPEARS TO HAVE TURNED TOWARD THE SOUTH AT ABOUT 6 KT. BUILDING HIGH PRESSURE TO THE NORTHWEST OF IRWIN SHOULD CAUSE THE STORM TO TURN TOWARD THE SOUTHWEST AND WEST OVER THE NEXT COUPLE OF DAYS. STEERING CURRENTS BECOME RATHER LIGHT AFTER THAT TIME...WITH THE GLOBAL MODELS IN POOR AGREEMENT IN THE MEDIUM RANGE. A COMPROMISE IS TO SHOW LITTLE MOTION AFTER 48 HOURS...WHICH RESULTS IN THE NEW FORECAST BEING BASICALLY AN UPDATE OF THE PREVIOUS ONE...ON THE SLOW END OF THE GUIDANCE SUITE. FORECAST POSITIONS AND MAX WINDS INIT 15/0900Z 17.2N 106.6W 35 KT 40 MPH 12H 15/1800Z 16.3N 106.8W 30 KT 35 MPH 24H 16/0600Z 15.3N 107.4W 30 KT 35 MPH 36H 16/1800Z 14.7N 108.1W 30 KT 35 MPH 48H 17/0600Z 14.7N 109.0W 30 KT 35 MPH 72H 18/0600Z 15.0N 110.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 19/0600Z 15.0N 110.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 20/0600Z...DISSIPATED $$ FORECASTER BLAKE