MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (LIONROCK) WARNING NR 30// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON 12W (LIONROCK), LOCATED APPROXIMATELY 247 NM SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED WEST-NORTHWESTWARD AT 02 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A SYSTEM WITH A WELL-DEFINED 10-NM EYE AND EXCELLENT RADIAL OUTFLOW WITH STRONG BIAS ON THE POLEWARD SIDE. BASED ON THE EYE-MOVEMENT, THE SYSTEM APPEARS TO HAVE SLOWED DOWN AND BEGUN A TIGHT CLOCKWISE LOOPING MOTION. THE INITIAL POSITION IS BASED ON THE EYE FEATURE IN THE MSI ANIMATION WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF 110 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF AGENCY AND OBJECTIVE DVORAK ESTIMATES RANGING FROM T5.2 TO T6.0. 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 A SLIGHT WEAKENING IN THE NEAR TERM. HOWEVER, BY TAU 48, 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 105 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 AND COOLING SSTS WILL GRADUALLY WEAKEN THE CYCLONE DOWN TO 55 KNOTS BY TAU 120. CONCURRENTLY, THE CYCLONE WILL ENTER THE BAROCLINIC ZONE AND BEGIN EXTRA-TROPICAL TRANSITION. NUMERIC GUIDANCE ARE IN AGREEMENT WITH THE REVERSAL IN THE TRACK TO A NORTHEAST POLEWARD TRAJECTORY. HOWEVER, THERE REMAINS A WIDE SPREAD IN THE MODEL ENVELOPE AND THE LATERAL SPEEDS OF EACH SOLUTION. IN VIEW OF THESE, THE CONFIDENCE IN THE JTWC TRACK FORECAST REMAINS LOW.// NNNN NNNN