WDPN31 PGTW 160300 MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W WARNING NR 06// RMKS/ 1. FOR METEOROLOGISTS. 2. 12 HOUR SUMMARY AND ANALYSIS. A. TROPICAL STORM (TS) 12W HAS WEAKENED SLIGHTLY OVER THE PAST 12 HOURS REMAINING A WEAK TS. FORWARD TRACK SPEED HAS INCREASED SIGNIFICANTLY AS THE STORM ACCELERATES TOWARD THE MID-LATITUDE FLOW PATTERN ON THE POLEWARD SIDE OF THE STEERING RIDGE AXIS. WHILE CONVECTION IS LESS WIDESPREAD ON THE NORTH- WESTERN SIDE OF THE CIRCULATION, THE STORM HAS STILL RETAINED A BROAD AREA OF DEEP CONVECTIVE BANDING ALONG THE SOUTHERN AND EASTERN PERIPHERIES OF THE LOW LEVEL CIRCULATION CENTER (LLCC). B. THE CURRENT POSITION IS BASED ON RECENT SATELLITE FIXES FROM PGTW AND RJTD AND A 152301Z 37H SSMIS PASS. THE CURRENT INTENSITY ESTIMATE IS BASED ON DVORAK T-NUMBERS OF 3.0 FROM KNES AND 2.5 FROM PGTW AND RJTD ALONG WITH A 152003Z QSCAT PASS DEPICTING 35 KNOT WINDS NEAR THE LLCC. TS 12W IS TRACKING EAST-NORTHEASTWARD ALONG THE NORTHWESTERN PERIPHERY OF A SUBTROPICAL STEERING RIDGE TO THE SOUTHEAST. THE TROPICAL STORM IS POLEWARD OF THE AXIS OF AN UPPER LEVEL ANTICYCLONE, AND IS BEGINNING TO EXPERIENCE A SIGNIFI- CANT INCREASE IN VERTICAL WIND SHEAR AS INTERACTION WITH THE MID- LATITUDE FLOW TO THE NORTH INCREASES. THIS INCREASED VERTICAL SHEAR COUPLED WITH LOWER SEA SURFACE TEMPERATURES AND THE INTRUSION OF DRIER MID-LATITUDE AIR IS SERVING TO SEVERELY WEAKEN THE STORM AS IT TRACKS FURTHER POLEWARD. 3. FORECAST REASONING A. THE FORECAST REASONING HAS NOT CHANGED SINCE THE PREVIOUS ISSUE OF THE PROGNOSTIC REASONING MESSAGE. B. TS 12W WILL CONTINUE TO ACCELERATE GENERALLY EAST-NORTHEAST- WARD ALONG THE POLEWARD PERIPHERY OF THE CURRENT STEERING RIDGE TOWARD THE MID-LATITUDE WESTERLY FLOW PATTERN. THE CYCLONE WILL ENCOUNTER RAPIDLY INCREASING VERTICAL WIND SHEAR AND DECREASING SEA SURFACE TEMPERATURES AFTER TAU 12, AS IT BEGINS TO TAKE ON EXTRA- TROPICAL CHARACTERISTICS. THE CYCLONE WILL BECOME FULLY EMBEDDED IN THE BAROCLINIC ZONE BY TAU 24. THE NUMERICAL MODEL GUIDANCE IS IN EXCELLENT AGREEMENT WITH THE CURRENT FORECAST. FORECAST TEAM: CHARLIE// NNNN