MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (NEOGURI) WARNING NR 020// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 21W (NEOGURI), LOCATED APPROXIMATELY 402 NM SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHEASTWARD AT 20 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A FULLY-EXPOSED, BROAD LOW-LEVEL CIRCULATION WITH DEEP CONVECTION SHEARED TO THE NORTHEAST. A 210659Z SSMIS 91GHZ COLOR COMPOSITE MICROWAVE IMAGE DEPICTS A WEAK FRONTAL STRUCTURE WITH PERSISTENT DEEP CONVECTION OVER THE NORTHERN SEMICIRCLE. OVERALL, THERE IS GOOD CONFIDENCE IN THE CURRENT POSITION. THE SYSTEM IS EMBEDDED WITHIN A DEEP MIDLATITUDE SHORTWAVE TROUGH AND HAS CONTINUED TO RAPIDLY DECAY UNDER A HOSTILE ENVIRONMENT CHARACTERIZED BY STRONG (55 KNOTS) VERTICAL WIND SHEAR. THE CURRENT INTENSITY IS ASSESSED CONSERVATIVELY AT 45 KNOTS BASED ON A KNES CURRENT INTENSITY ESTIMATE OF 3.0 (45 KNOTS) AND RECENT ASCAT DATA SHOWING 40-45 KNOT WIND NORTHERLY WINDS. TS 21W IS TRACKING QUICKLY NORTHEASTWARD ALONG THE NORTHERN FLANK OF THE SUBTROPICAL RIDGE WITHIN THE STRONG MIDLATITUDE WESTERLY FLOW. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 21W IS FORECAST TO CONTINUE TRACKING NORTHEASTWARD THROUGH THE FORECAST PERIOD AND IS EXPECTED TO COMPLETE EXTRA-TROPICAL TRANSITION WITHIN THE NEXT 12 HOURS. AFTER TRANSFORMING INTO A COLD- CORE LOW, THE SYSTEM WILL TRACK SOUTH OF TOKYO AND THEN EAST OF HONSHU MAINTAINING GALE-FORCE WINDS. DUE TO THE BROAD NATURE OF THE LOW, THERE IS UNCERTAINTY IN THE EXACT CENTER LOCATION AND TRACK. NUMERICAL MODEL GUIDANCE CONTINUES TO STRUGGLE WITH THIS COMPLEX TRANSITION, THEREFORE, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK AFTER TAU 12.// NNNN NNNN