MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (LIONROCK) WARNING NR 33// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON 12W (LIONROCK), LOCATED APPROXIMATELY 265 NM SOUTHEAST OF KADENA AB, HAS TRACKED EAST-SOUTHEASTWARD AT 04 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED AND MULTISPECTRAL SATELLITE IMAGERY SHOW AN IMPROVING CONVECTIVE SYMMETRY ASSOCIATED WITH TY 12W. A 252219Z SSMIS 91GHZ MICROWAVE IMAGE DEPICTS CONVECTIVE BANDS WRAPPING AROUND THE SOUTH AND SOUTHEAST OF THE LOW-LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH GOOD CONFIDENCE. DVORAK ESTIMATES REMAIN AT T5.5 ACROSS ALL AGENCIES, AND THE OVERALL CONVECTIVE STRUCTURE HAS REMAINED STEADY STATE IN THE LAST 6 HOURS. THE CURRENT INTENSITY IS THUS MAINTAINED AT 105 KNOTS. TY 12W HAS FINALLY BEGUN TO DRIFT TOWARD THE EAST AS THE SUBTROPICAL RIDGE (STR) AXIS TO THE NORTH BEGINS TO RETREAT TOWARD THE WEST. CIMSS ANALYSIS SUGGESTS THAT SOME NORTHEASTERLY VERTICAL WIND SHEAR (15 TO 20 KNOTS) PERSISTS OVER THE SYSTEM, BUT THE IMPROVED SYMMETRY OF THE DEEP CONVECTION AROUND TY 12W SUGGEST THAT THE SHEAR HAS BEGUN TO RELAX. 3. FORECAST REASONING. A. THERE IS NO CHANGE IN THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE, EXCEPT A SLIGHT INCREASE IN THE INTENSITY FORECAST. B. TY 12W IS COMPLETING A SLOW LOOP TOWARD THE EAST, AND IT IS EXPECTED TO BEGIN A TRACK TOWARD THE NORTHEAST AHEAD OF A SHORTWAVE TROUGH THAT WILL EVOLVE INTO A HIGH-AMPLITUDE, EXTRATROPICAL SYSTEM OVER THE KOREAN PENINSULA. AS THE STR AXIS GIVES WAY TO THE SOUTHWESTERLY UPPER-TROPOSPHERIC FLOW, THE POLEWARD OUTFLOW CHANNEL WILL BE ENHANCED, GIVEN TY 12W A WINDOW OF OPPORTUNITY TO INTENSIFY FROM TAU 24 TO 48. THE FORECAST FOR A PEAK INTENSITY OF AROUND 110 KNOTS AROUND TAU 48 IS SLIGHTLY HIGHER THAN THE INTENSITY CONSENSUS BUT IS ABOUT 10 KNOTS BELOW THE DYNAMICAL HWRF GUIDANCE. AFTER TAU 48, VERTICAL WIND SHEAR SHOULD BEGIN TO INCREASE AS TY 12W INTERACTS WITH THE DEEPENING AND NEGATIVELY TILTED TROUGH OVER THE SEA OF JAPAN. C. BEYOND TAU 72, EXTRATROPICAL CYCLOGENESIS IS EXPECTED TO OCCUR IN THE SEA OF JAPAN ASSOCIATED WITH THE AFOREMENTIONED TROUGH. THIS, TOGETHER WITH A HIGH-AMPLITUDE RIDGE THAT IS FORECAST TO BUILD OVER THE SEA OF OKHOTSK, WILL LEAD TO A COMPLEX STEERING FLOW THAT SHOULD TURN TY 12W SHARPLY TO THE NORTHWEST INTO JAPAN. THE EXACT TIMING OF THIS TURN IS STILL HIGHLY UNCERTAIN, BUT THE SUITE OF NUMERICAL MODEL TRACKERS HAS COME INTO AGREEMENT WITH THIS TURN. AROUND TAU 96 AND BEYOND, INCREASING VERTICAL WIND SHEAR AND INTERACTION WITH THE STRONG BAROCLINIC ZONE ASSOCIATED WITH THE MID-LATITUDE TROUGH OVER THE SEA OF JAPAN WILL RESULT IN AN EXPANSION OF THE WIND FIELD OF TY 12W PRIOR TO LANDFALL AS IT BEGINS TO TRANSITION INTO AN EXTRATROPICAL CYCLONE. POSSIBLE IMPACTS OF THIS LARGER WIND FIELD SHOULD BE CONSIDERED ACCORDINGLY. OVERALL, ALTHOUGH CERTAINTY OF A JAPAN LANDFALL IS INCREASING, CONFIDENCE IN THE EXACT JTWC TRACK FORECAST REMAINS LOW IN THE EXTENDED TAUS.// NNNN NNNN