WDPN31 PGTW 012100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (TWENTYSEVEN) WARNING NR 003// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 14.5N 128.3E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 424 NM EAST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 15 KTS SIGNIFICANT WAVE HEIGHT: 15 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL STORM 27W IS SHOWING SIGNS OF CONSOLIDATION AND SPREADING CONVECTION OVER THE PAST SIX HOURS, ALTHOUGH THAT IS TO BE EXPECTED DURING A DIURNAL MAXIMUM PHASE. NONETHELESS, DEEP CONVECTION HAS BECOME ESTABLISHED OVER THE NORTHWEST QUADRANT AND WIND FLOW IS TIGHTENING AROUND THE VORTEX, WHICH IS ALSO TUCKING ITSELF FURTHER UNDERNEATH THE CONVECTION. THE INTENSITY IS BUMPED UP TO 35KTS WHICH IS THE TOP END OF THE 30-35 KT OVERALL RANGE OF THE STORM. BASED ON THREE CONSECUTIVE T2.5 FROM JTWC AND RISING OBJECTIVE ASSESSMENTS FROM ADT, AIDT, DMINT, AND DPRINT WHICH ARE ALL AT 34KTS, THE 35KTS IS CLOSER TO THE TRUE INTENSITY THAN 30KTS. THE SYSTEM IS MOVING THROUGH THE FERTILE GROUNDS OF THE PHILIPPINE SEA UNDER AN AREA OF MINIMAL VERTICAL WIND SHEAR AND SEA SURFACE TEMPERATURES NEARING 30C. ANIMATED WATER VAPOR IMAGERY SHOWS SOME MILD SUBSIDENCE AND DRIER AIR ALONG THE TRACK TO THE NORTHWEST OF THE STORM, BUT ANIMATED IMAGERY AND GUIDANCE INDICATES THAT THE SYSTEM HAS COCOONED ITSELF AND WILL BE ABLE TO CARRY ITS MOISTURE WITH IT TO THE LUZON COAST. A 011709Z AMSR TWO SERIES HOT OFF THE PRESS SERVED TO VERIFY POSITIONING AS WELL AS STRONGLY SUPPORTING 35KTS. INITIAL WIND RADII BASIS: A 251001Z ASCAT UPSTREAM OF THE SYSTEM WAS USED TO SHAPE THE WESTERN HEMISPHERE RADII, OTHERWISE THE OBJECTIVE BEST TRACK WAS USED. CURRENT STEERING MECHANISM: THE SOUTHERN FLANK OF THE SUBTROPICAL RIDGE, WHICH IS ANCHORED IN A MID-LEVEL ANTICYCLONE CENTERED JUST NORTHEAST OF TAIWAN. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.0 - 30 KTS KNES: T3.0 - 45 KTS CIMSS SATCON: 40 KTS AT 011653Z CIMSS ADT: 34 KTS AT 011730Z CIMSS AIDT: 34 KTS AT 011730Z CIMSS D-MINT: 34 KTS AT 011653Z CIMSS D-PRINT: 34 KTS AT 011800Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE RADIAL ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: THE SUBTROPICAL RIDGE IS WELL ESTABLISHED AND WILL GUIDE THE SYSTEM ALONG A STEADY WEST-NORTHWEST BEARING TO A LANDFALL BETWEEN PALANAN AND CASIGURAN. THE FAVORABLE ENVIRONMENT WILL ALLOW THE SYSTEM TO RAMP UP TO AT OR ABOVE TYPHOON STRENGTH PRIOR TO LANDFALL. THE RUGGED TERRAIN OF NORTHERN LUZON WILL TEAR THE SYSTEM UP AND MAKE IT DIFFICULT TO TRACK UNTIL IT TRACKS OFF-SHORE SOMEWHERE NEAR VIGAN AND REGATHERS ITSELF OVER THE WEST PHILIPPINE SEA. THE ENVIRONMENT BETWEEN LUZON AND HAINAN IS ALSO VERY FAVORABLE, WITH ANOTHER STRETCH OF LOW VERTICAL WIND SHEAR AND PLENTY OF DEEP MOISTURE OVER THE SOUTHERN PORTION OF THE STORM TO ALLOW IT TO DEEPEN TO TYPHOON STRENGTH BEFORE APPROACHING COASTAL CHINA. MODEL DISCUSSION: THERE ARE NO ISSUES WITH TRACK GUIDANCE. THE JTWC FORECAST STAYS BETWEEN THE MULTI-MODEL CONSENSUS AND THE HAFS-A AND NEW AI-DERIVED TRACKERS. FOR THE MOST PART, INTENSITY GUIDANCE DOES NOT PROCESS THE TRIP OVER LUZON, BUT HAFS-A SHOWS A GOOD SENSITIVITY TO THAT LEG. IT DOES, HOWEVER, TRACK THE SYSTEM ACROSS LUZON AT 55KTS. THE MOST DIFFICULT POINTS OF THE FORECAST COME AT TAU 36, CAPTURING HOW MUCH THE TERRAIN DEGRADES THE SYSTEM, AND AT TAU 48, HOW MUCH IT IS ABLE TO RAMP BACK UP ONCE RETURNING TO SEA. THE JTWC INTENSITY FORECAST TOPS OUT AT 75KTS, WHICH MATCHES HAFS-A AND IS JUST BELOW THE CONSENSUS MEAN. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 00-72 HR: LOW INTENSITY 72-120 HR: LOW// NNNN