MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (LIONROCK) WARNING NR 25// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON 12W (LIONROCK), LOCATED APPROXIMATELY 274 NM EAST- SOUTHEAST OF KADENA AB, HAS TRACKED SOUTHWESTWARD AT 08 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A WELL DEFINED EYE FEATURE WITH A SPIRAL BANDING WRAPPING INTO THE LOW LEVEL CIRCULATION CENTER. THE POSITION IS BASED ON SATELLITE FIXES FROM PGTW WITH GOOD CONFIDENCE. THE INITIAL INTENSITY IS ASSESSED AT 75 KNOTS AND IS BASED ON OBJECTIVE DVORAK ESTIMATES FROM ALL AGENCIES REPORTING T4.0 (75 KNOTS). UPPER-LEVEL ANALYSIS INDICATES THE PRESENCE OF RADIAL OUTFLOW THAT HAS IMPROVED SOME IN THE LAST SIX HOURS DUE TO OPENING DISTANCE FROM THE ANTICYCLONE POSITIONED SOUTH OF THE SYSTEM. VERTICAL WIND SHEAR VALUES ARE CURRENTLY VERY FAVORABLE DIRECTLY OVER THE SYSTEM. TY 12W IS LOCATED WITHIN A WEAK STEERING ENVIRONMENT BETWEEN THE DOMINANT WESTERN SUBTROPICAL RIDGE (STR) AND EASTERN STR, AND IS DRIFTING GENERALLY SOUTHWESTWARD. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 12W WILL REMAIN TRAPPED WITHIN THIS COMPETING STEERING ENVIRONMENT WHILE DRIFTING SOUTHWESTWARD THROUGH TAU 36. BEYOND TAU 36 THE EASTERN STEERING RIDGE WILL BUILD IN FROM THE SOUTH AND SHIFT THE TRACK ABRUPTLY TO THE NORTHEAST. TS 12W IS FORECAST TO GRADUALLY INTENSIFY UNDER FAVORABLE CONDITIONS TO A PEAK OF 85 KNOTS BY TAU 24. HOWEVER, OCEANIC HEAT CONTENT IS LOW AND UPWELLING DUE TO A PERIOD OF QUASI- STATIONARY MOTION AS THE STEERING RIDGES SHIFT WILL PREVENT FURTHER INTENSIFICATION. C. IN THE EXTENDED TAUS, THE NEAR-EQUATORIAL RIDGE WILL KEEP TY 12W TRACKING NORTHEASTWARD AS A DEEP MIDLATITUDE TROUGH DEEPENS OVER JAPAN, PROVIDING AN EXHAUST MECHANISM ALLOWING THE SYSTEM TO BRIEFLY INTENSIFY AS IT MOVES INTO WARMER WATERS. WHILE THE MODEL VORTEX TRACKERS DIFFER ON THE EXACT NATURE OF THE TURN EASTWARD, THE TRACKERS ALL SHOW AN EASTWARD TURN WITH DIFFERENT TRACK SPEEDS. DUE TO THE COMPLEXITY OF THE STEERING ENVIRONMENT AND UNCERTAINTY IN THE EASTWARD TURN, THERE IS LOW CONFIDENCE IN JTWC FORECAST TRACK.// NNNN NNNN