WDPN32 PGTW 220300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (AMPIL) WARNING NR 18// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 12W (AMPIL), LOCATED APPROXIMATELY 338 NM NORTH- NORTHEAST OF TAIPEI, TAIWAN, HAS TRACKED WEST-NORTHWESTWARD AT 12 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS SIGNIFICANT CONVECTION WRAPPING AROUND THE NORTHERN HALF OF THE LOW LEVEL CIRCULATION CENTER (LLCC) AND MUCH LESS CONVECTION SOUTH OF THE LLCC. THE INITIAL POSITION IS PLACED WITH GOOD CONFIDENCE BASED ON A 202240Z SSMIS 91 GHZ IMAGE CLEARLY SHOWING THE CONVECTION WRAPPING AROUND THE LLCC. THE INITIAL INTENSITY OF 45 KNOTS IS BASED ON MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATES OF T3.0 (45 KNOTS). ENVIRONMENTAL ANALYSIS SHOWS GOOD POLEWARD OUTFLOW, LOW VERTICAL WIND SHEAR (5-10 KNOTS) AND WARM SEA SURFACE TEMPERATURES (28-29C) BEING COUNTERED BY DRIER AIR ENTRAINING IN FROM THE SOUTH. TS 12W IS TRACKING NORTHWESTWARD ALONG THE WESTERN EDGE OF THE SUBTROPICAL RIDGE (STR) LOCATED TO THE EAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 12W WILL CONTINUE ON A NORTHWESTERLY TRACK ALONG THE WESTERN PERIPHERY OF THE STR FOR THE REMAINDER OF THE FORECAST. TS 12W WILL BEGIN SLOWLY WEAKENING AS IT MOVES OVER LAND JUST NORTH OF SHANGHAI, CHINA IN THE NEXT 6 HOURS. THAT WEAKENING TREND WILL CONTINUE UNTIL TS 12W FULLY DISSIPATES BY TAU 48. THE NUMERICAL MODEL GUIDANCE HAS CONSISTENTLY SHIFTED EASTWARD IN THE LATER TAUS (TAU 48 AND BEYOND) AS THE CYCLONE BEGINS TO INTERACT WITH THE MID- LATITUDE WESTERLIES AND THE TRACK BECOMES NORTHEASTWARD. THE FORECAST CALLS FOR TS 12W TO FALL BELOW 25 KNOTS PRIOR TO GOING EXTRATROPICAL DUE TO LAND INTERACTION BUT THE CIRCULATION MAY PERSIST BEYOND TAU 48. DESPITE THE UNCERTAINTY BEYOND TAU 48, THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN