WDPN31 PGTW 091500 MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (NESAT) WARNING NR 42// RMKS/ 1. FOR METEOROLOGISTS. 2. PROGNOSTIC REASONING FOR 091200Z TO 101200Z JUN 2005 A. TROPICAL STORM (TS) 04W (NESAT), LOCATED APPROXIMATELY 405 NM SOUTH-SOUTHWEST OF TOKYO, JAPAN, HAS TRACKED NORTHEASTWARD AT 11 KNOTS OVER THE PAST 06 HOURS. RECENT ANIMATED ENHANCED INFRARED AND WATER VAPOR IMAGERY REVEALS A COMPLETE BREAKDOWN OF DEEP CONVECTION DUE TO EXTRATROPICAL TRANSITION. B. TS 04W IS CURRENTLY DOWNSTREAM FROM A DEVELOPING UPPER-LEVEL LOW WHICH IS SITUATED JUST SOUTHEAST OF THE RYUKYU ISLAND CHAIN. THE STORM IS FORECAST TO REMAIN ON A NORTHEAST TRACK AHEAD OF THE LOW AND EQUATORWARD OF THE SUBTROPICAL JET (STJ). AFTER TAU 12, TS 04W IS EXPECTED TO ACCELERATE AS IT MERGES WITH THE STJ. THE AVAILABLE DYNAMIC AIDS CONSISTING OF MM5, GFDN, COAMPS, WBAR, AVN, EGRR, JTYM, NOGAPS, AND JJGS ARE IN GOOD AGREEMENT THROUGH THE FORECAST PERIOD WITH THE EXCEPTION OF MM5 AND WBAR. THIS FORECAST IS BASED ON A BLEND OF THE AVAILABLE DYNAMIC AIDS. C. DURING THE LAST 12 HOURS, TS 04W HAS LOST THE EYE AND DRY-AIR ENTRAINMENT HAS ERODED THE DEEP CONVECTION ALONG THE SOUTHERN SEMI- CIRCLE. THE SYSTEM IS UNDERGOING EXTRATROPICAL TRANSITION WITH POS- SIBLE FRONTOGENESIS. POLEWARD OUTFLOW REMAINS STRONG, HOWEVER THE LOSS OF DEEP CONVECTION HAS RESULTED IN SIGNIFICANT WEAKENING. THE SYSTEM WILL BECOME A FULLY EXTRATROPICAL LOW WITHIN 24 HOURS. D. CURRENT WIND RADII ARE BASED ON A 090910Z SSMI PASS. FORECAST WIND RADII ARE BASED ON CLIMATOLOGY FOR AN AVERAGE-SIZED SYSTEM UNDERGOING EXTRATROPICAL TRANSITION. 3. FORECAST TEAM: BRAVO// NNNN