MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 23W (SONGDA) WARNING NR 13// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 23W (SONGDA), LOCATED APPROXIMATELY 537 NM SOUTHEAST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHEASTWARD AT 10 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS A 10-NM EYE THAT IS BECOMING CLOUD-FILLED AS THE SYSTEM BECOMES MORE RAGGED AND ELONGATED DUE TO HIGH VERTICAL WIND SHEAR (VWS) ASSOCIATED WITH THE MID-LATITUDE WESTERLIES. THE CURRENT POSITION IS BASED ON THE EYE FEATURE WITH HIGH CONFIDENCE. THE INTENSITY OF 90 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF AGENCY AND OBJECTIVE DVORAK ESTIMATES AND REFLECTS THE DEGRADATION. UPPER LEVEL ANALYSIS INDICATES THE SYSTEM HAS DRIFTED DEEPER INTO THE PREVAILING WESTERLIES WITH STRONG (25-30 KNOT) VWS. THE CYCLONE HAS BEGUN TO ACCELERATE NORTHEASTWARD ON THE POLEWARD SIDE OF THE SUBTROPICAL RIDGE. 3. FORECAST REASONING. A. NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY SONGDA WILL CONTINUE ACCELERATING NORTHEASTWARD AS IT EMBEDS DEEPER WITHIN THE MID-LATITUDE WESTERLY FLOW. INCREASING VWS AND COOLING SEA SURFACE TEMPERATURES WILL RAPIDLY ERODE THE SYSTEM. BY TAU 24, TY 23W WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT) AND BY THE END OF THE FORECAST PERIOD, THE SYSTEM WILL COMPLETE ETT AND BE REDUCED TO A 40-KNOT COLD-CORE LOW. THERE IS HIGH CONFIDENCE IN THE FORECAST DUE TO VERY TIGHT AGREEMENT IN ALL MODEL TRACKERS.// NNNN NNNN