MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (NEOGURI) WARNING NR 019// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 21W (NEOGURI), LOCATED APPROXIMATELY 521 NM SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED NORTH-NORTHEASTWARD AT 19 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTI-SPECTRAL SATELLITE IMAGERY SHOWS THE SYSTEM IS BEING SIGNIFICANTLY SHEARED NORTHEASTWARD AS IT HAS MOVED UNDER AN AREA OF VERY STRONG (45-50 KTS) UPPER-LEVEL SOUTHWESTERLY FLOW INDUCED BY A DEEP TROUGH TO THE WEST. THE SYSTEM HAS ALREADY BEGUN TRANSITIONING INTO AN EXTRA-TROPICAL COLD-CORE LOW AS IT HAS BEGUN INTERACTING WITH THE BAROCLINIC ZONE. THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE DUE TO THE BROADENING NATURE OF THE LOW-LEVEL CIRCULATION, ASSOCIATED WITH THE EXTRA-TROPICAL TRANSITION (ETT). THE INITIAL INTENSITY OF 55 KTS IS BASED ON AN AVERAGE OF AGENCY DVORAK ESTIMATES RANGING FROM 3.0 (45 KTS) TO 4.0 (65 KTS). AS PREVIOUSLY MENTIONED THE SYSTEM IS EXPERIENCING VERY STRONG (45-50KT) VERTICAL WIND SHEAR (VWS), ALBEIT PARTIALLY OFFSET BY ROBUST POLEWARD OUTFLOW. TS 21W IS TRACKING NORTHEAST AROUND THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) TO THE EAST. 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 QUICKLY TO THE NORTHEAST REMAINING OFF THE SOUTHEAST COAST OF JAPAN AND BY TAU 36 TS 21W WILL TRACK PAST TOKYO AND BE SOUTH OF NORTHERN HONSHU. VWS IS EXPECTED TO INCREASE EVEN MORE (> 65KTS) AND BY TAU 24, THE SYSTEM WILL COMPLETE ETT AND TRANSFORM INTO A COLD-CORE LOW WITH AN EXPANDING, STRONG GALE-FORCE WIND FIELD EMBEDDED IN THE BAROCLINIC ZONE. CONSEQUENTLY, THE LOW LEVEL CIRCULATION CENTER WILL CONTINUE TO BE DIFFICULT TO PINPOINT THROUGHOUT THE ETT. MODEL GUIDANCE HAS REMAINED WIDELY ERRATIC WITH SEVERAL MODELS HAVING ISSUES TRACKING THE VORTEX AS IT TRACKS INSIDE THE BAROCLINIC ZONE. OVERALL, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN NNNN