MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (LIONROCK) WARNING NR 34// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON 12W (LIONROCK), LOCATED APPROXIMATELY 279 NM SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED EASTWARD AT 04 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A SYSTEM WITH A WELL-DEFINED 6-NM EYE AND EXCELLENT DUAL OUTFLOW. BASED ON THE EYE-MOVEMENT, THE SYSTEM HAS BEEN QUASI-STATIONARY AND HAS, OVERALL, MAINTAINED CONVECTIVE DEPTH. THE INITIAL POSITION IS BASED ON THE EYE FEATURE IN THE MSI ANIMATION WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF 105 KNOTS IS BASED ON CONGRUENT DVORAK ESTIMATES FROM PGTW, KNES, AND RJTD. UPPER LEVEL ANALYSIS INDICATES TY 12W IS UNDER A RIDGE AXIS IN AN AREA OF LOW (05-10 KNOT) VERTICAL WIND SHEAR (VWS). THE CYCLONE IS IN A WEAK STEERING ENVIRONMENT BETWEEN TWO REFLECTIONS OF THE SUBTROPICAL RIDGE (STR) - ONE TO THE NORTHWEST AND THE OTHER TO THE EAST-SOUTHEAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE IN THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 12W WILL BEGIN A SLOW NORTHEAST POLEWARD TRACK AS THE STR TO THE EAST-SOUTHEAST ASSUMES PRIMARY STEERING. ALTHOUGH SEA SURFACE TEMPERATURES (SSTS) AT 30 DEGREES CELSIUS AND OUTFLOW REMAIN ROBUST, INCREASING VWS WILL OFFSET THESE FAVORABLE DYNAMICS AND RESULT IN AN INTENSITY STAGNATION IN THE NEAR TERM. HOWEVER, BY TAU 36, INCREASED POLEWARD OUTFLOW DUE TO THE INITIAL EXPOSURE TO THE STRONG WESTERLIES ASSOCIATED WITH AN APPROACHING MID-LATITUDE TROUGH WILL CAUSE A SMALL REBOUND IN THE INTENSITY TO 110 KNOTS. C. IN THE EXTENDED TAUS, TYPHOON LIONROCK WILL BEGIN TO TRACK MORE NORTHWARD AS ANOTHER REFLECTION OF THE STR ANCHORED AT 45N JUST SOUTH OF KAMCHATKA BUILDS AND ASSUMES STEERING. INCREASING VWS, COOLING SSTS, AND TRACK ACROSS THE ISLAND OF HONSHU WILL GRADUALLY WEAKEN THE CYCLONE DOWN TO 40 KNOTS BY TAU 120. AT TAU 96, THE CYCLONE WILL ENTER THE BAROCLINIC ZONE AND BEGIN EXTRA-TROPICAL TRANSITION AND BECOME A COLD-CORE LOW IN THE SEA OF JAPAN BY END OF FORECAST. NUMERIC GUIDANCE REMAINS WIDELY SPREAD ACROSS THE MODEL ENVELOPE AND IN THE LATERAL SPEEDS OF EACH SOLUTION. IN VIEW OF THESE, THE CONFIDENCE IN THE JTWC TRACK FORECAST REMAINS LOW.// NNNN NNNN