WDPN32 PGTW 121500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (RAMMASUN) WARNING NR 09// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 09W (RAMMASUN), LOCATED APPROXIMATELY 187 NM WEST OF ANDERSEN AFB, GUAM, HAS TRACKED WESTWARD AT 15 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) REVEALS DEEPENING CENTRAL CONVECTION AS THE BROKEN FORMATIVE BANDING ALONG THE LEADING WESTERN EDGE HAS BECOME MORE PERSISTENT AND THE LOW LEVEL CIRCULATION CENTER (LLCC) IS BEGINNING TO CONSOLIDATE. A 121205Z AMSU-B MICROWAVE IMAGE ADDITIONALLY SHOWS IMPROVED LOW LEVEL STRUCTURE AS IMPROVED BANDING CAN BE OBSERVED DESPITE AN OVERALL SMALL CONVECTIVE SIGNATURE. 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). THERE IS LOW CONFIDENCE IN THE INITIAL POSITION DUE TO THE SOME AMBIGUITY IN THE EIR LOOP WHILE POSITION FIXES FROM ALL REPORTING AGENCIES REMAIN WIDELY SPREAD. THE CURRENT INTENSITY HAS BEEN INCREASED TO TROPICAL STORM STRENGTH (35 KNOTS) BASED ON THE IMPROVED LOW LEVEL STRUCTURE OF THE SYSTEM SEEN IN THE AFOREMENTIONED SATELLITE IMAGERY AND AS DVORAK INTENSITY ESTIMATES FROM PGTW AND RJTD HAVE INCREASED TO 35 KNOTS AS WELL. 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 WILL BEGIN TO 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. AFTER LANDFALL, THE TERRAIN OF LUZON WILL SIGNIFICANTLY WEAKEN THE SYSTEM AS IT MOVES INTO THE SOUTH CHINA SEA. MODEL GUIDANCE IS IN GOOD AGREEMENT; HOWEVER, DUE TO THE LOW CONFIDENCE IN THE INITIAL POSITIONING, THE OVERALL CONFIDENCE IN THE FORECAST REMAINS LOW.// NNNN