WDPN32 PGTW 260300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (EWINIAR) WARNING NR 09// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 19W (EWINIAR), LOCATED APPROXIMATELY 40 NM NORTH OF IWO-TO, JAPAN, HAS TRACKED EAST-NORTHEASTWARD AT 08 KNOTS OVER THE PAST SIX HOURS. THE CURRENT POSITION IS BASED ON A PGTW SATELLITE FIX AND A 252150Z TRMM PASS. THE CURRENT INTENSITY OF 50 KNOTS IS CONSISTENT WITH RECENT DVORAK CURRENT INTENSITY ESTIMATES AND LOW-LEVEL STRUCTURE EVIDENT IN THE TRMM PASS. TS 19W IS MOVING NORTHEASTWARD ALONG THE WESTERN PERIPHERY OF A SUBTROPICAL STEERING RIDGE TO THE EAST. DEEP CONVECTION REMAINS CONFINED TO THE EASTERN PERIPHERY OF THE LOW-LEVEL CIRCULATION CENTER (LLCC) DUE TO PERSISTENT VERTICAL WIND SHEAR INDUCED BY EASTERLY FLOW AHEAD OF AN UPPER-LEVEL TROUGH TO THE WEST. 3. FORECAST REASONING. A. NO CHANGE IN THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 19W IS FORECAST TO TURN FROM A NORTHEASTWARD TRACK TO A NORTHWARD TRACK IN THE UPCOMING 12 HOURS AS THE STEERING RIDGE WEAKENS WITH THE APPROACH OF THE AFOREMENTIONED TROUGH CURRENTLY ANALYZED TO THE WEST OF THE CYCLONE. BETWEEN TAU 24 AND TAU 48, TS 19W IS EXPECTED TO SLOW SIGNIFICANTLY AS IT INTERACTS WITH AN UPPER- LEVEL LOW DEVELOPING AT THE BASE OF THE APPROACHING TROUGH. THEREAFTER, TS 19W WILL ACCELERATE NORTHEASTWARD AHEAD OF A SECOND MIDLATITUDE TROUGH. THE SYSTEM IS EXPECTED TO INTENSIFY A BIT OVER THE NEXT 24 HOURS WITH STRONG DIFFLUENCE ALOFT AND PASSAGE OVER WARM WATER. AS THE CYCLONE ENCOUNTERS A BAROCLINIC ZONE AFTER TAU 48 IT WILL WEAKEN SLOWLY AND BEGIN EXTRATROPICAL TRANSITION. C. IN THE EXTENDED PERIOD, TS 19W WILL ACCELERATE NORTHEASTWARD AHEAD OF A MIDLATITUDE TROUGH AND COMPLETE EXTRATROPICAL TRANSITION BY TAU 96. INCREASING VERTICAL WIND SHEAR AND PASSAGE OVER COOLER WATER WILL ALLOW SLOW WEAKENING TO CONTINUE AS THE SYSTEM COMPLETES THE TRANSITION INTO A COLD CORE LOW. THE NUMERICAL MODEL GUIDANCE IS IN GOOD OVERALL AGREEMENT AND THE CURRENT TRACK FORECAST LIES SLIGHTLY AHEAD OF THE CONSENSUS IN THE EXTENDED PERIOD. THERE IS HIGH CONFIDENCE IN ALL TAUS OF THE CURRENT FORECAST TRACK.// NNNN