MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (LIONROCK) WARNING NR 32// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON 12W (LIONROCK), LOCATED APPROXIMATELY 247 NM SOUTHEAST OF KADENA AB, HAS TRACKED SOUTHWESTWARD AT 03 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY INDICATES DEEP CONVECTION CONTINUING TO WRAP AROUND THE LOW-LEVEL CIRCULATION CENTER (LLCC) OF TY 12W, WITH THE EYE DISAPPEARING AND REAPPEARING INTERMITTENTLY OVER THE LAST 24 HOURS. THE INITIAL POSITION IS PLACED WITH GOOD CONFIDENCE WITH THE AID OF EIR ANIMATIONS AND 251801Z GMI 89GHZ MICROWAVE IMAGERY SHOWING DEEP CONVECTION WRAPPING AROUND THE SOUTHWEST SIDE OF THE LLCC. THE CURRENT INTENSITY IS ASSESSED AT 105 KNOTS BASED ON DVORAK ESTIMATES OF T5.5 ACROSS ALL AGENCIES. OVERALL, TY 12W HAS STEADILY MAINTAINED ITS INTENSITY AND CONVECTIVE STRUCTURE IN THE LAST 24 HOURS, DESPITE MINOR INTENSITY FLUCTUATIONS. WEAK NORTHEASTERLY VERTICAL WIND SHEAR (5 TO 15 KNOTS) CONTINUES TO AFFECT THE SYSTEM DUE TO AN EASTWARD EXTENSION OF THE SUBTROPICAL RIDGE (STR) SITUATED OVER CHINA. THIS RIDGE CONTINUES TO RESTRICT POLEWARD OUTFLOW BUT IS BEGINNING TO RETREAT TO THE WEST. TY 12W HAS BEEN EXHIBITING SOME ERRATIC MOTION DUE TO ITS POSITION IN A REGION OF WEAK STEERING FLOW BETWEEN THE STR TO THE NORTHWEST AND A NEAR-EQUATORIAL RIDGE TO THE SOUTHEAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE IN THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE, EXCEPT A SHIFT OF THE TRACK WESTWARD FROM TAU 96 TO 120. B. TY 12W CONTINUED TO DRIFT FURTHER SOUTHWEST SINCE THE LAST WARNING, BUT A TURN TOWARD THE NORTHEAST IS IMMINENT. SOME SLIGHT WEAKENING IS FORECAST IN THE NEAR TERM GIVEN THE RESTRICTED POLEWARD OUTFLOW AND WEAK ALBEIT PERSISTENT NORTHEASTERLY VERTICAL WIND SHEAR ACROSS TY 12W. AS THE STR AXIS TO THE NORTH RETREATS WESTWARD OVER CHINA, A SHORTWAVE TROUGH NEAR LAKE BAIKAL WILL AMPLIFY AND DIG OVER THE KOREAN PENINSULA. THIS WILL FORCE TY 12W TO ACCELERATE TOWARD THE NORTHEAST WITH A WINDOW OF OPPORTUNITY TO INTENSIFY FROM TAU 36 TO 48 AS THE POLEWARD OUTFLOW CHANNEL OPENS UP. C. BEYOND TAU 72, EXTRATROPICAL CYCLOGENESIS IS EXPECTED TO OCCUR IN THE SEA OF JAPAN ASSOCIATED WITH A DEEP, NEGATIVELY-TILTED MID- LATITUDE TROUGH STEERING TY 12W TOWARD THE NORTHEAST THEN NORTH. MEANWHILE, A HIGH-AMPLITUDE RIDGE IS EXPECTED TO DEVELOP OVER THE SEA OF OKHOTSK, WHICH WILL DRIVE TY 12W TOWARD THE NORTHWEST. THERE IS STILL SIGNIFICANT UNCERTAINTY ASSOCIATED WITH THE TIMING OF THIS EVENTUAL TURN, BUT CONFIDENCE IS GRADUALLY INCREASING FOR A POTENTIAL IMPACT TO JAPAN. THE MAJORITY OF NUMERICAL MODEL TRACK GUIDANCE SUGGESTS THIS TURN WILL OCCUR, WITH THE GFS, HWRF, AND GFDN BEING OUTLIERS WITH TRACKS THAT CONTINUE TOWARD THE NORTHEAST. GIVEN THE INCREASING VERTICAL WIND SHEAR, COOLER SSTS, AND EXTRATROPICAL TRANSITION, STEADY WEAKENING IS FORECAST BEYOND TAU 72. HOWEVER, GIVEN THE DYNAMICS OF INTERACTIONS WITH THE DEEP, HIGH-AMPLITUDE TROUGH AND EXTRATROPICAL CYCLOGENESIS OVER THE SEA OF JAPAN, IMPACTS ASSOCIATED WITH THE LARGER WIND FIELD OF A TRANSITIONING TROPICAL SYSTEM SHOULD EVENTUALLY BE CONSIDERED. FOR NOW, THE CONFIDENCE IN THE JTWC TRACK FORECAST REMAINS LOW IN THE EXTENDED TAUS.// NNNN NNNN