WDPN31 PGTW 170300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SANBA) WARNING NR 26// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON 17W (SANBA), LOCATED APPROXIMATELY 75 NM SOUTHWEST OF PUSAN, SOUTH KOREA, HAS TRACKED NORTHWARD AT 17 KNOTS OVER THE PAST SIX HOURS. THE CURRENT POSITION IS BASED ON RECENT SATELLITE FIXES FROM PGTW AND RJTD AND RADAR DATA FROM JAPAN AND KOREA. THE CURRENT INTENSITY OF 80 KNOTS IS CONSISTENT WITH DVORAK ESTIMATES FROM KNES, PGTW, AND RJTD. TY 17W IS TRACKING POLEWARD IN THE GRADIENT BETWEEN A SUBTROPICAL STEERING RIDGE EAST OF JAPAN AND A MIDLATITUDE TROUGH TO THE NORTHWEST OF THE CYCLONE. RECENT ANIMATED MULTISPECTRAL SATELLITE IMAGERY INDICATES THAT EXTRATROPICAL TRANSITION HAS BEGUN, WITH SOUTHWESTERLY VERTICAL WIND SHEAR AHEAD OF THE APPROACHING TROUGH DISPLACING MOST OF THE CONVECTION TO THE NORTH OF THE LOW LEVEL CIRCULATION CENTER (LLCC) AND STRATOCUMULUS CLOUD LINES WRAPPING INTO THE LLCC FROM THE NORTHWEST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 17W WILL ACCELERATE NORTH-NORTHEASTWARD ACROSS THE KOREAN PENINSULA OVER THE NEXT 24 HOURS AND COMPLETE EXTRATROPICAL TRANSITION BY TAU 12. ALTHOUGH INTERACTION WITH THE TAEBAEK MOUNTAIN RANGE AND INCREASING VERTICAL WIND SHEAR ARE EXPECTED TO INDUCE STEADY WEAKENING, THE SYSTEM SHOULD MAINTAIN GALE-FORCE INTENSITY UNDER THE INFLUENCE STRONG POLEWARD DIVERGENCE ALOFT DURING EXTRATROPICAL TRANSITION. THE AVAILABLE NUMERICAL GUIDANCE REMAINS IN VERY TIGHT AGREEMENT. THE CURRENT FORECAST LIES SLIGHTLY AHEAD OF THE MODEL CONSENSUS IN ANTICIPATION OF A STRONGER STEERING FLOW THAN DEPICTED IN MANY OF THE CONSENSUS MEMBER MODEL FIELDS. THERE IS HIGH CONFIDENCE IN THE TRACK FORECAST.// NNNN