WDPN31 PGTW 181500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (ONE) WARNING NR 006// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 01W (DAJUAN), LOCATED APPROXIMATELY 772 NM EAST-SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 03 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) IMAGERY SHOWS A PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER ON THE EASTERN EDGE OF FLARING CONVECTION. THE OVERALL AVERAGE MOTION OF THE LLCC HAS BEEN TO THE WEST HOWEVER, THE LLCC APPEARS TO HAVE TRACKED IN A SMALL COUNTER-CLOCKWISE LOOP OVER THE PAST SIX HOURS. THERE HAVE BEEN NO RECENT MICROWAVE IMAGES TO ASSIST WITH FIXING THE POSITION OF TS 01W, HENCE THERE IS ONLY FAIR CONFIDENCE IN THE INITIAL POSITION BASED ON AN ANALYSIS OF THE WEAK LOW-LEVEL BANDS THAT ARE EVIDENT ON THE EASTERN SIDE OF THE CIRCULATION. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON A STRONG AGREEMENT BETWEEN MULTI-AGENCY DVORAK INTENSITY ESTIMATES FROM PGTW, KNES AND RJTD OF T2.5 (35 KTS) TO T3.0 (45 KTS), AN ADT ESTIMATE OF T2.5 AND A SATCON ESTIMATE OF 37 KNOTS. ENVIRONMENTAL ANALYSIS REVEALS MARGINAL CONDITIONS CHARACTERIZED BY MODERATE TO HIGH (20-25 KNOTS) EASTERLY VERTICAL WIND SHEAR (VWS) BEING OFFSET SOMEWHAT BY ROBUST DIFFLUENT POLEWARD OUTFLOW. SST VALUES REMAIN CONDUCIVE AT 29-30C. TS 01W IS MEANDERING SLOWLY WESTWARD IN A WEAK STEERING PATTERN TO THE SOUTH OF A BREAK IN THE SUBTROPICAL RIDGE (STR). 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE IN THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 01W IS LOCATED WITHIN A WEAK STEERING ENVIRONMENT RESULTING FROM THE PRESENCE OF A MAJOR SHORTWAVE TROUGH EXTENDING FROM JAPAN TO EAST OF TAIWAN, CREATING A COL REGION BETWEEN TWO STR CENTERS; ONE OVER CENTRAL VIETNAM AND THE OTHER TO THE NORTHEAST OF THE GUAM. OVER THE NEXT 24 HOURS THE MAJOR SHORTWAVE TROUGH WILL RAPIDLY FILL AND MOVE EASTWARD, ALLOWING FOR A RETURN TO MORE ZONAL FLOW TO THE NORTH OF THE STR. IN RESPONSE, THE EASTERN STR CENTER IS EXPECTED TO EXTEND WESTWARD, PUSHING TS 01W ON A SLOW WESTWARD TRACK THROUGH TAU 36. AFTER TAU 48, TS 01W WILL BEGIN TO TRACK MORE WEST-NORTHWESTWARD AS THE STR TO THE EAST MOVES OVER GUAM WHILE SIMULTANEOUSLY THE STR TO THE WEST RECEDES AND WEAKENS AHEAD OF THE APPROACH OF A MAJOR SHORTWAVE TROUGH OVER SOUTHERN CHINA. TS 01W IS EXPECTED TO MAKE LANDFALL ALONG THE NORTHEAST COAST OF MINDANAO NEAR TAU 60 BEFORE CONTINUING NORTHWEST INTO THE BOHOL SEA. OVERALL, NUMERICAL MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT THROUGH TAU 48, THOUGH THE UKMET AND UKMET ENSEMBLE MEAN REMAIN SIGNIFICANT POLEWARD OUTLIERS. HOWEVER, BY TAU 72, THE GUIDANCE BEGINS TO SHOW SIGNIFICANT CROSS TRACK UNCERTAINTY AS THE GFS AND GFS ENSEMBLE TURN THE SYSTEM DUE WEST. THE REMAINDER OF THE CONSENSUS MEMBERS ARE IN A TIGHT CLUSTER CENTERED ABOUT THE CONSENSUS MEAN. AS CONFIRMED BY THE SATELLITE DEPICTION, VWS REMAINS THE DOMINANT FACTOR IN SUPPRESSING DEVELOPMENT AT THIS TIME. VWS IS FORECAST TO WEAKEN TO MORE MODERATE LEVELS OVER THE NEXT 12-24 HOURS WHICH WILL ALLOW FOR SLOW INTENSIFICATION TO A PEAK OF 50 KNOTS BY TAU 36. THERE IS HOWEVER CONSIDERABLE UNCERTAINTY IN THE INTENSITY FORECAST DUE TO THE STEADY EASTERLY VWS AND HOW MUCH THE STRONG POLEWARD OUTFLOW WILL OFFSET THE SHEAR. C. THE SYSTEM IS FORECAST TO CONTINUE TRACKING ALONG THE WESTERN BOUNDARY OF THE DEEP-LAYER STR LOCATED TO THE EAST THROUGH THE EXTENDED FORECAST PERIOD. AFTER LANDFALL, THE SYSTEM WILL TRACK OVER THE MAIN ISLANDS OF THE SOUTHWESTERN PHILIPPINES AND BE SIGNIFICANTLY IMPACTED BY TERRAIN INTERACTION, WEAKENING IT TO ONLY 30 KNOTS BY TAU 96. BY TAU 96, AS THE SYSTEM EMERGES INTO THE SOUTH CHINA SEA, REDUCED OUTFLOW, ENTRAINMENT OF DRY AIR AND INCREASING VWS WILL LEAD TO FURTHER WEAKENING TO ONLY 25 KNOTS BY TAU 120. DISCOUNTING THE UKMET AND UKMET ENSEMBLE OUTLIERS, THERE REMAINS A HIGH DEGREE OF UNCERTAINTY IN THE NUMERICAL MODEL GUIDANCE, WITH A 300NM SPREAD BETWEEN THE GFS AND THE NAVGEM TRACKERS WHICH DEFINE THE OUTER EDGES OF THE GUIDANCE ENVELOPE. THE JTWC FORECAST TRACK LIES JUST SOUTH OF THE MULTI-MODEL CONSENSUS, CLOSE TO THE ECMWF SOLUTION WITH OVERALL LOW CONFIDENCE IN THE EXTENDED PORTION OF THE FORECAST.// NNNN