UNCLAS//N03144// MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 31W (PONGSONA) WARNING NR 18// RMKS/ WDPN31 PGTW 070300 1. FOR METEOROLOGISTS. 2. PROGNOSTIC REASONING FOR 070000Z7 TO 100000Z1 DEC 02. A. TYPHOON (TY) 31W (PONGSONA), LOCATED APPROXIMATELY 310 NM SOUTHEAST OF GUAM, HAS TRACKED NORTHWESTWARD AT 11 KNOTS OVER THE PAST SIX HOURS. THE WARNING POSITION IS BASED ON 062330Z4 VISIBLE AND ENHANCED INFRARED SATELLITE IMAGERY. THE WARNING INTENSITY IS BASED ON SATELLITE CURRENT INTENSITY ESTIMATES OF 90 AND 102 KNOTS. A 062231Z4 SPECIAL SENSOR MICROWAVE IMAGER (SSM/I) PASS REVEALED A 20 NM EYE. B. THE DEVELOPING BAROCLINIC SYSTEM EAST OF JAPAN HAS WEAKENED THE SUBTROPICAL RIDGE RESULTING IN A NORTHWESTWARD TRACK FOR TY 31W OVER THE LAST 12 HOURS. ANOTHER DEVELOPING BAROCLINIC SYSTEM IS EXPECTED TO MOVE OFF OF JAPAN IN 24 HOURS. THIS SYSTEM IS FORECAST TO FURTHER WEAKEN THE SUBTROPICAL RIDGE RESULTING IN A POLEWARD TRACK FOR TY 31W AFTER 24 HOURS. AFTER 48 HOURS THE SYSTEM IS EXPECTED TO BEGIN INTERACTING WITH THE MID-LATITUDE WESTERLIES AND BEGIN TRANSITION TO AN EXTRATROPICAL SYSTEM. THE AVAILABLE DYNAMIC AIDS CONSISTING OF NOGAPS, NCEP AVIATION (AVN), JAPAN GLOBAL (JGSM) AND TYPHOON (JTYM), AND UKMET (EGRR), COAMPS, AFWA MM5 AND AUSTRALIAN TCLAPS MODELS ARE IN GOOD AGREEMENT WITH THIS SCENARIO. COAMPS, AFWA MM5, AND TCLAPS REMAIN THE OUTLIERS WITH COAMPS MAINTAINING A WESTWARD RECURVATURE BIAS AND MM5 AND TCLAPS HAVING A EASTWARD RECURVATURE BIAS. OUR FORECAST IS BASED ON A CONSENSUS OF THE AVAILABLE DYNAMIC AIDS. C. TY 31W IS EXPECTED TO REACH MAXIMUM INTENSITY IN 24 HOURS AS THE SYSTEM TRACKS UNDER THE UPPER LEVEL RIDGE AXIS. TY 31W IS EXPECTED TO BEGIN SLOWLY WEAKENING AFTER 36 HOURS AS IT STARTS TO INTERACT WITH THE MID-LATITUDE FLOW NORTH OF THE RIDGE. D. INITIAL WIND RADII AND FORECAST WIND RADII ARE BASED ON CLIMATOLOGY FOR AN LARGE-SIZED SYSTEM. FORECAST TEAM: LEEJOICE/RONSEE/SHERRY/EDBERG//