MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (TALIM) WARNING NR 37// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 20W (TALIM), LOCATED APPROXIMATELY 128 NM NORTH- NORTHWEST OF YOKOTA AB, HAS TRACKED NORTHEASTWARD AT 47 KNOTS OVER THE PAST SIX HOURS. THE CURRENT POSITION IS PLACED WITH LOW CONFIDENCE BASED ON MULTIAGENCY POSITION FIXES AND ANIMATED RADAR IMAGERY FROM JMA. THE POOR OVERALL STRUCTURE OF THE STORM LENDS A HIGH DEGREE OF UNCERTAINTY IN THE POSITION. THE INITIAL INTENSITY OF 55 KNOTS IS CONSISTENT WITH SYNOPTIC OBSERVATIONS AND SLIGHTLY BELOW A PGTW EXTRATROPICAL CURRENT INTENSITY ESTIMATE OF T4.0 (65 KNOTS). TS 20W CONTINUES TO RAPIDLY ACCELERATE TO THE NORTHEAST AS IT TRACKS BETWEEN A SUBTROPICAL RIDGE TO THE SOUTHEAST AND A MID-LATITUDE TROUGH TO THE NORTHWEST. THE ENVIRONMENT HAS BECOME INCREASINGLY UNFAVORABLE AS THE STORM TRACKS OVER COOL (25 CELSIUS) WATERS AND THROUGH AN AREA OF HIGH (50+ KNOTS) VERTICAL WIND SHEAR. TS TALIM HAS BEGUN EXTRATROPICAL TRANSITION AS EVIDENT BY THE ASYMMETRIC SHAPE AND RAPID ACCELERATION IN FORWARD MOTION AS IT MERGES WITH THE MID-LATITUDE TROUGH. 3. FORECAST REASONING. A. THE FORECAST TRACK HAS AGAIN SHIFTED SLIGHTLY TO THE EAST BASED ON THE RECENT STORM MOTION. HOWEVER, THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 20W WILL CONTINUE TO TRACK TO THE NORTHWEST FOR THE DURATION OF THE FORECAST PERIOD. THE SYSTEM IS FORECAST TO COMPLETE EXTRATROPICAL TRANSITION. INTERACTION WITH THE MID-LATITUDE TROUGH THROUGHOUT THE TRANSITION WILL ALLOW 20W TO MAINTAIN AN EXPANSIVE AREA OF GALE FORCE WINDS. GIVEN THE SIZE AND INTENSITY OF THE WIND FIELD, POTENTIALLY SIGNIFICANT WEATHER IMPACTS ARE POSSIBLE THROUGHOUT JAPAN FOR THE NEXT 24 HOURS. DESPITE THE SLIGHT EASTWARD SHIFT IN THE MODEL GUIDANCE, CONTINUED TIGHT AGREEMENT AMONG MODELS LENDS HIGH CONFIDENCE IN THE CURRENT JTWC OFFICIAL TRACK FORECAST.// NNNN NNNN