MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 22W (PRAPIROON) WARNING NR 42// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 22W (PRAPIROON), LOCATED APPROXIMATELY 150 NM EAST OF KADENA AIR BASE, OKINAWA, JAPAN, HAS TRACKED NORTHEASTWARD AT 13 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS A SINGULAR BAND OF DEEP CONVECTION LOCATED ALONG THE NORTHWESTERN QUADRANT AND IS WRAPPING ALONG THE SOUTHERN PERIPHERY TOWARDS THE LOW LEVEL CIRCULATION CENTER (LLCC). THE BAND HAS BEEN FLARING OVER THE PAST 12 HOURS AND IS APPROACHING DIURNAL MAXIMUM, WHICH IS HELPING TO ENHANCE THE IMPROVING POLEWARD OUTFLOW CHANNEL. UPPER LEVEL ANALYSIS INDICATES THE LEADING EDGE OF AN APPROACHING MID-LATITUDE TROUGH IS INCREASING THE EFFECTIVE POLEWARD VENTING OF THE LLCC WITH AN ANTICYCLONE LOCATED TO THE EAST CREATING A LOW VERTICAL WIND SHEAR (VWS) ENVIRONMENT. A TOTAL PRECIPITABLE WATER (TPW) IMAGE INDICATES A DRY RIBBON OF AIR HAS COMPLETELY SURROUNDED THE LLCC. THE DRY AIR HAS YET TO PENETRATE THE CENTER OF THE LLCC, BUT A LOOP OF TPW IMAGERY SHOWS A DIMINISHING WARM, MOIST AIR MASS AS THE LLCC HAS LOST CONTACT TO THE LARGER TROPICAL AIR MASS TO THE SOUTH. THE SYSTEM IS BEING STEERED BY THE WESTERN EDGE OF A DEEP SUBTROPICAL RIDGE (STR) ANCHORED TO THE EAST. IT HAS BEGUN TO ACCELERATE NORTHEASTWARD IN RESPONSE TO THE TROUGH DIGGING ALONG THE WESTERN EDGE OF THE STR. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING BULLETIN. B. TS PRAPIROON WILL CONTINUE TO ACCELERATE NORTHEASTWARD AND BEGIN EXTRA-TROPICAL TRANSITION BEFORE TAU 36, BECOMING A COLD CORE LOW BY TAU 72. THE SYSTEM IS FORECAST TO BRIEFLY INTENSIFY OVER THE NEXT 12 HOURS DUE TO THE ENHANCED POLEWARD OUTFLOW, HOWEVER THIS WILL BE SHORT LIVED WITH THE DECREASING SEA SURFACE TEMPERATURES, LOST CONNECTION TO THE TROPICAL AIR MASS, AND INCREASING VWS BEYOND TAU 12. BEYOND TAU 12 THE ENVIRONMENT WILL QUICKLY BECOME UNFAVORABLE LEADING TO THE EXTRA-TROPICAL TRANSITION PROCESS TO BEGIN. AVAILABLE NUMERIC MODEL GUIDANCE IS IN VERY TIGHT AGREEMENT, LENDING HIGH CONFIDENCE FOR THIS FORECAST.// NNNN NNNN