MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (VONGFONG) WARNING NR 42// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 19W (VONGFONG), LOCATED APPROXIMATELY 102 NM SOUTH-SOUTHEAST OF SASEBO, JAPAN, HAS TRACKED EAST-NORTHEASTWARD AT 19 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A BROAD, NOW FULLY-EXPOSED, LOW-LEVEL CIRCULATION CENTER (LLCC) WITH LIMITED DEEP CONVECTION SHEARED OVER THE NORTHERN SEMI-CIRCLE OF THE LLCC. A 122322Z SSMIS MICROWAVE IMAGE ADDITIONALLY SHOWS THE OVERALL STRUCTURE IS STARTING TO ELONGATE AS IT BEGINS TO ENCOUNTER LAND. DUE TO THE BROADENING NATURE OF THE LLCC THERE IS DECREASING CONFIDENCE IN THE INITIAL POSITION AND MOTION. THE INITIAL INTENSITY ASSESSMENT HAS BEEN DECREASED TO 5O KNOTS AS THE OBSERVATIONS ACROSS KYUSHU SUGGEST THE SYSTEM HAS WEAKENED. DVORAK INTENSITY ESTIMATES CONTINUE TO FALL AS THE CONVECTIVE ORGANIZATION WEAKENS AND MAY BE UNREPRESENTATIVE OF THE CURRENT INTENSITY. UPPER-LEVEL ANALYSIS, ALONG WITH ANIMATED WATER VAPOR IMAGERY, REVEALS A HOSTILE ENVIRONMENT AS STRONG (30 TO 40 KNOTS) SOUTHWESTERLY VERTICAL WIND SHEAR IS OFFSETTING ENHANCED POLEWARD OUTFLOW INTO THE MIDLATITUDE WESTERLIES. TS 19W IS ACCELERATING TO THE NORTHEAST AS IT TRACKS ALONG THE NORTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR). 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 19W IS FORECAST TO CONTINUE TO ACCELERATE TO THE NORTHEAST THROUGH THE REMAINDER OF THE FORECAST PERIOD AS AN APPROACHING MIDLATITUDE TROUGH DIGS IN FROM THE KOREAN PENINSULA AND PRESSES ON THE STR. AS THE SYSTEM GAINS LATITUDE AND DRAGS ACROSS JAPAN, EXTRA- TROPICAL TRANSITION (ETT) WILL BEGIN DUE TO THE SYSTEM BECOMING EMBEDDED IN THE MID-LATITUDE WESTERLIES. ETT, ALONG WITH INCREASED LAND INTERACTION, WILL INDUCE A WEAKENING TREND AS THE SYSTEM BROADENS AND GAINS BAROCLINIC ENERGY WITH THE STRONGEST WINDS MIGRATING INTO THE DEVELOPING FRONTAL FEATURES. TS 19W IS EXPECTED TO COMPLETE ETT BY TAU 24 AS IT APPROACHES THE KANTO PLAIN AS A GALE FORCE, COLD-CORE, LOW. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT WITH THE FORECAST SCENARIO AND TRACK; THEREFORE, THERE IS HIGH CONFIDENCE IN THE FORECAST.// NNNN NNNN