WDPN31 PGTW 011500 MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 06W (NANGKA) WARNING NR 05// RMKS/ 1. FOR METEOROLOGISTS. 2. PROGNOSTIC REASONING FOR 011200Z4 TO 041200Z7 JUN 03. A. TROPICAL STORM (TS) 06W (NANGKA), LOCATED APPROXIMATELY 170 NM WEST OF NORTHERN LUZON, PHILIPPINES, HAS DRIFTED NORTHEASTWARD AT 05 KNOT OVER THE PAST 06 HOURS. THE WARNING POSITION IS BASED ON 011130Z6 INFRARED SATELLITE IMAGERY. THE WARNING INTENSITY IS BASED ON SATELLITE CURRENT INTENSITY ESTIMATES OF 35 TO 45 KNOTS. ANIMATED INFRARED SATELLITE IMAGERY DEPICTS DEEP CONVECTION IN THE NORTHEAST REGION OF THE SYSTEM. ANIMATED WATER VAPOR SATELLITE IMAGERY AND THE RECENT MICROWAVE DATA ALSO INDICATE DRY AIR ENTRAINMENT CONTINUES FROM THE NORTHWEST OF THE SYSTEM. B. TS 06W IS FORECAST TO CONTINUE TRACKING SLOWLY TO THE NORTHEAST UNDER THE INFLUENCE OF THE STEERING RIDGE TO THE EAST OF THE SYSTEM. AFTERWARDS, TRACK SPEED IS FORECAST TO INCREASE AS THE SYSTEM FALLS UNDER THE INFLUENCE OF THE MID-LATITUDE WESTERLIES, BEGINNING EXTRATROPICAL TRANSITION BY THE END OF THE FORECAST PERIOD. THE AVAILABLE DYNAMIC AIDS CONSISTING OF NOGAPS, UKMET (EGRR), GFDN, THE JAPANESE GLOBAL (JGSM) AND TYPHOON MODELS (JTYM), AND NCEP GFS FALL INTO TWO CLUSTERS WITH REGARD TO THIS FORECAST. NOGAPS AND GFDN KEEP THE SYSTEM UNDER A WEAKER STEERING INFLUENCE AND ADVANCE THE SYSTEM SLOWER THAN THE OTHER MODELS. THIS FORECAST IS BASED ON PERSISTENCE AND A CONSENSUS OF ALL THE DYNAMIC AIDS WITH AN EMPHASIS ON EGRR, JGSM, JTYM, AND GFDN. C. TS 06W REMAINS IN A MODERATE UPPER LEVEL ENVIRONMENT AND WILL DEVELOP AT LESS THAN A CLIMATOLOGICAL RATE. NEAR THE END OF THE PERIOD EXTRATROPICAL TRANSITION AND INCREASING VERTICAL WIND SHEAR WILL HALT TROPICAL DEVELOPMENT. D. FORECAST WIND RADII ARE BASED ON CLIMATOLOGY FOR AN AVERAGE- SIZED SYSTEM. FORECAST TEAM: MAZANY/KLINZMANN/COOK/BIRD// NNNN