MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (RAMMASUN) WARNING NR 10// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 09W (RAMMASUN), LOCATED APPROXIMATELY 257 NM WEST OF ANDERSEN AFB, GUAM, HAS TRACKED WESTWARD AT 13 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY REVEALS DEEPENING CENTRAL CONVECTION REMAINS BROKEN AROUND THE LOW LEVEL CIRCULATION CENTER (LLCC) AS DEVELOPMENT OF THE UPPER LEVEL OUTFLOW CONTINUES TO STRUGGLE. THE CURRENT POSITION OF THE LLCC IS BASED ON A POSITION FIX FROM PGTW AND A RECENT 121711Z GPM 36 GHZ MICROWAVE PASS SHOWING WEAK LOW LEVEL BANDING. THE CURRENT INTENSITY HAS BEEN MAIN- TAINED AT 35 KNOTS BASED UPON THE DVORAK ESTIMATE FROM PGTW, BUT KNES AND RJTD WERE INDICATING A SLIGHTLY WEAKER SYSTEM AS THE CONVECTION TEMPORARILY WEAKENED IN THE PAST SIX HOURS. UPPER-LEVEL ANALYSIS REVEALS AN UNCHANGED, MARGINAL ENVIRONMENT CHARACTERIZED BY WEAKLY DIFFLUENT EASTERLY OUTFLOW AND LOW TO MODERATE (10 TO 15 KNOTS) VERTICAL WIND SHEAR (VWS). TS 09W CONTINUES TO TRACK ALONG THE SOUTHERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) THAT IS ANCHORED TO THE NORTH OF THE SYSTEM. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST TRACK PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING BULLETIN. B. TS 09W IS FORECAST TO TRACK WESTWARD FOR THE NEXT 72 HOURS ALONG THE SOUTHERN PERIPHERY OF THE ENTRENCHED STR. ENVIRONMENTAL CONDITIONS WILL REMAIN MARGINAL FOR THE NEXT 36 TO 48 HOURS, LEADING TO A SLOW INTENSIFICATION PROCESS. NEAR TAU 72, VWS WILL BEGIN TO DECREASE AND OUTFLOW IMPROVE, ALLOWING FOR INCREASED INTENSIFICATION AS THE SYSTEM APPROACHES THE SOUTHWESTERN EDGE OF THE STR. C. AFTER TAU 72, A MID-LATITUDE TROUGH IS FORECAST TO DIG OVER EASTERN CHINA, WHICH WILL MODIFY THE STR, LEADING TO A MORE WEST- NORTHWEST TRACK TOWARDS LUZON. FAVORABLE SEA SURFACE TEMPERATURES IN THE PHILIPPINE SEA ALONG WITH INCREASED OUTFLOW WILL LEAD TO A MAXIMUM INTENSITY AS THE SYSTEM APPROACHES LAND, REACHING 95 KNOTS BEFORE LANDFALL, WHICH IS CURRENTLY NOT REFLECTED IN THE FORECAST DUE TO TIMING OF FORECAST POSITIONS AND THE TIMING OF LANDFALL WITH LUZON. AFTER LANDFALL, THE TERRAIN OF LUZON WILL SIGNIFICANTLY WEAKEN THE SYSTEM AS IT MOVES INTO THE SOUTH CHINA SEA. BETWEEN TAU 96 AND TAU 108 THERE WILL BE FURTHER WEAKENING TO AS LOW AS 65 KNOTS BUT BY TAU 120 THE ENVIRONMENT, IN ASSOCIATION WITH MODEL GUIDANCE, INDICATES A SLIGHT INCREASE IN THE INTENSITY OF THE SYSTEM TO 75 KNOTS. MODEL GUIDANCE IS IN GOOD AGREEMENT; HOWEVER, DUE TO THE LOW CONFIDENCE IN THE UPPER LEVEL ENVIRONMENT, THE CONFIDENCE IN THE FORECAST REMAINS LOW.// NNNN NNNN