MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (VONGFONG) WARNING NR 38// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 19W (VONGFONG), LOCATED APPROXIMATELY 79 NM NORTH OF KADENA AB, OKINAWA, HAS TRACKED NORTH-NORTHWESTWARD AT 09 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) REVEALS A CONTINUED WEAKENING TREND AS COLD AIR STRATOCUMULUS CLOUDS CAN BE OBSERVED STREAMING INTO THE WESTERN PERIPHERY OF THE SYSTEM WHILE THE LOW LEVEL CIRCULATION CENTER (LLCC) HAS BECOME OPEN AND ELONGATED. A RECENT 112336Z SSMIS MICROWAVE IMAGE SHOWS THE CONVECTIVE ORGANIZATION HAS ALMOST COMPLETELY DIMINISHED AS THE ONLY REMAINING DEEP CONVECTION HAS BECOME CONTAINED TO THE NORTHERN FLANK. DUE TO THE BROAD ORGANIZATION OF THE LLCC, THERE IS ONLY FAIR CONFIDENCE IN THE INITIAL POSITION AND DIRECTION. THE INITIAL INTENSITY HAS BEEN DECREASED TO 60 KNOTS BASED ON DECREASING DVORAK INTENSITY ESTIMATES THAT RANGE FROM 55 TO 77 KNOTS AND AN 120052Z ASCAT PASS. UPPER LEVEL ANALYSIS, ALONG WITH ANIMATED WATER VAPOR IMAGERY, REVEALS A DEGRADING ENVIRONMENT AS STRONG (30 TO 40 KNOTS) SOUTHWESTERLY VERTICAL WIND SHEAR IS OFFSETTING GOOD POLEWARD OUTFLOW INTO THE MIDLATITUDE WESTERLIES. TY 19W IS TRACKING NORTHWARD 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 EXPECTED TO CONTINUE TO TRACK GENERALLY NORTH OVER THE NEXT 12 HOURS ALONG THE NORTHWESTERN PERIPHERY OF THE STR. AFTER WHICH, A DEEP MID-LATITUDE TROUGH, WHICH IS CURRENTLY DRAPED ACROSS EASTERN CHINA, IS EXPECTED TO PROPAGATE EAST AND RE-ORIENT THE STR. THIS WILL ACCELERATE THE SYSTEM TO NORTHEAST ACROSS SOUTHERN JAPAN. AS THE SYSTEM ACCELERATES AND BECOMES FURTHER EMBEDDED INTO THE MID- LATITUDE WESTERLIES, THE SYSTEM WILL BROADEN AND GAIN FRONTAL CHARACTERISTICS AS IT BEGINS EXTRA-TROPICAL TRANSITION (ETT) NEAR TAU 24. DUE TO THE CURRENTLY UNFAVORABLE UPPER-LEVEL ENVIRONMENT AND EXPECTED ETT, THE SYSTEM IS FORECAST TO GENERALLY WEAKEN AS THE STRONGEST WINDS ASSOCIATED WITH THE SYSTEM MIGRATE FROM THE CENTER OF THE SYSTEM INTO THE DEVELOPING FRONTS. THE SYSTEM IS EXPECTED TO BECOME A GALE FORCE, MID-LATITUDE LOW BY TAU 48 AS IT MOVES ACROSS THE KANTO PLAIN. DYNAMIC MODEL GUIDANCE IS IN VERY GOOD AGREEMENT WITH THE FORECAST SCENARIO AND TRACK, LENDING TO HIGH CONFIDENCE IN THE FORECAST.// NNNN NNNN