WDPN31 PGTW 030300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (YAGI) WARNING NR 007// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.3N 119.5E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 238 NM NORTH-NORTHWEST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 12 KTS SIGNIFICANT WAVE HEIGHT: 17 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: BASED ON ALL AVAILABLE DATA, IT IS ASSESSED THE TROPICAL STORM (TS) 12W (YAGI) HAS MOVED BACK OVER THE OPEN WATERS WEST OF NORTHERN LUZON AND IS IN THE PROCESS OF MERGING WITH A SECONDARY CIRCULATION THAT WAS PREVIOUSLY LOCATED WEST OF LINGAYEN GULF. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A WELL-DEFINED LOW LEVEL CIRCULATION CENTER (LLCC) NOW WEST OF LAOAG CITY, WITH DEEP CONVECTIVE CELLS (HOT TOWERS) DEVELOPING INTO CONVECTIVE BANDS TO THE WEST AND SOUTH OF THE ASSESSED CENTER AND BEGINNING TO WRAP UPSHEAR TO THE EAST SIDE. WHILE THE EXACT LLCC IS OBSCURED, THERE IS A RELATIVELY CLEAR AREA IN THE MSI, AND WHILE THIS IS AN EYE IN THE TRUEST SENSE, IT IS GENERALLY IN THE SAME AREA AS THE LLCC. A 022252Z SSMIS 37GHZ MICROWAVE IMAGE REVEALED A PEANUT SHAPED LOW EMISSIVITY REGION (LER), SUGGESTIVE OF AN ONGOING MERGER OF THE TWO CIRCULATION CENTERS ASSOCIATED WITH THE LEE-SIDE JUMP. THE RAPID IMPROVEMENT IN THE OVERALL STRUCTURE SEEN IN THE MSI LOOP SUPPORTS THE FACT THAT THIS MERGER IS HAPPENING MORE QUICKLY THAN ORIGINALLY ANTICIPATED. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE USING AN EXTRAPOLATION OF THE LER IN THE MICROWAVE IMAGERY NOTED ABOVE. THE INITIAL INTENSITY IS SET AT 40 KNOTS WITH HIGH CONFIDENCE, BASED ON AN AVERAGE OF THE AGENCY DVORAK CURRENT INTENSITY ESTIMATES, SUPPORTED BY MULTIPLE OBJECTIVE ESTIMATES NOTED BELOW. THE INITIAL WIND RADII ARE ASSESSED WITH HIGH CONFIDENCE BASED ON A RECENT SHIP OBSERVATION LOCATED 60NM TO THE NW, REPORTING 33 KNOT WINDS, AS WELL AS RECENT SCATTEROMETER DATA. ANALYSIS REVEALS A FAVORABLE AND IMPROVING ENVIRONMENT, CHARACTERIZED BY LOW EASTERLY SHEAR, MODERATE EASTWARD OUTFLOW ENHANCING AN ALREADY ESTABLISHED EQUATORWARD OUTFLOW CHANNEL AND ZESTY SSTS. THE SYSTEM IS TRACKING WEST-NORTHWESTWARD ALONG THE SOUTHERN SIDE OF A STR OVER CENTRAL CHINA, THOUGH THE PAST SIX HOUR MOTION APPEARS FASTER THAN IT ACTUALLY IS DUE TO THE LEE-SIDE JUMP. INITIAL WIND RADII BASIS: PERSISTENCE, SCATTEROMETER DATA AND SHIP OBSERVATIONS. CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER STR CENTERED OVER CHINA. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.5 - 35 KTS RCTP: T2.5 - 35 KTS KNES: T3.0 - 45 KTS CIMSS SATCON: 41 KTS AT 030100Z CIMSS ADT: 39 KTS AT 020000Z CIMSS DPRINT: 40 KTS AT 030100Z CIMSS DMINT: 35 KTS AT 022218Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 31-32 CELSIUS OUTFLOW: MODERATE EQUATORWARD OTHER FACTORS: MODERATE EASTWARD OUTFLOW. ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: HIGH INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: HAVING MOVED BACK OVER WATER, TS 12W HAS RAPIDLY MERGED WITH THE SECONDARY CIRCULATION PREVIOUSLY SEEN WEST OF LINGAYEN GULF ABOUT 12 HOURS AGO. EARLIER MICROWAVE IMAGERY SUGGESTS THIS PROCESS IS ALREADY WELL-ALONG AND WILL LIKELY COMPLETE MUCH FASTER THAN ANTICIPATED. THE FACT THAT THE MERGER WILL HAPPEN FASTER THAN THOUGHT MEANS THAT THE IMPACT TO THE FORECAST TRACK WILL BE LESSENED. A REDUCTION IN TRACK SPEED IS STILL ANTICIPATED AS THE SYSTEM CONSOLIDATES THE VORTEX. ADDITIONALLY, THE ECMWF GLOBAL MODELS FIELDS IN PARTICULAR, INDICATE A MESOSCALE RIDGE PUSHING SOUTHWARD FROM HONG KONG INTO THE SOUTH CHINA SEA (SCS) OUT OF THE STR OVER CHINA. THIS FEATURE WILL SERVE TO SLOW THE FORWARD MOTION FOR THE FIRST 24 HOURS OF THE FORECAST, BEFORE IT LIFTS OUT OF THE WAY AND THE RIDGE BECOMES MORE EAST-WEST ORIENTED. TRACK SPEEDS PICK UP A NOTCH AFTER TAU 24, AND THE SYSTEM CONTINUES AT A CONSISTENT SPEED THROUGH TAU 72. BEGINNING AROUND TAU 48, BOTH THE ALONG- AND CROSS-TRACK SPREAD BEGINS TO INCREASE SHARPLY, WITH THE GFS-BASED MODELS TURNING NORTHWESTWARD WHILE THE ECMWF TURNS WEST-SOUTHWESTWARD, SUCH THAT THE GUIDANCE BRACKETS HAINAN AS THE SYSTEM APPROACHES LANDFALL JUST AFTER TAU 72. THE JTWC TRACK THROUGH TAU 72 REMAINS CONSISTENT WITH THE PREVIOUS FORECAST, HEDGED JUST NORTH OF THE CONSENSUS MEAN. IN THE EXTENDED FORECAST, THE SPREAD OF THE GUIDANCE CONTINUES TO GROW, WITH POTENTIAL TRACKS SPREAD EVENLY ACROSS A BAND FROM SOUTH OF HONG KONG TO NORTHERN VIETNAM, DUE TO SIGNIFICANT DIFFERENCES IN THE DEPICTION OF THE STEERING RIDGE IN TERMS OF BOTH STRENGTH AND POSITION. THE GFS CONTINUES TO SHIFT THE RIDGE TO THE EAST ALLOWING FOR A MORE WEST-NORTHWESTWARD TRACK, WHILE THE ECMWF MAINTAINS A STRONGER RIDGE FURTHER TO THE WEST, LEADING TO A MORE WESTWARD TRACK. IN TERMS OF INTENSITY, THE SYSTEM IS SLOWLY INTENSIFYING FOR THE NEXT 12 TO 24 HOURS AS IT CONTINUES TO CONSOLIDATE THE VORTEX. ONCE FIRMLY ESTABLISHED AND VERTICALLY ALIGNED (WHICH MAY OCCUR FASTER THAN CURRENTLY EXPECTED), THE PACE OF INTENSIFICATION WILL PICK UP A NOTCH. AFTER TAU 24, THE SYSTEM MOVES OVER A POOL OF VERY WARM, HIGH OHC WATERS, DEVELOPS STRONG UPPER-LEVEL ANTICYCLONE (ULAC) OVER TOP AND A RECEIVES A BIT OF AN ENHANCEMENT IN OUTFLOW EASTWARD INTO A TUTT-CELL. THE ALIGNMENT OF THESE FACTORS WILL LEAD TO A PERIOD OF RAPID INTENSIFICATION (RI), PEAKING BETWEEN TAU 60 AND 72, AT OR ABOVE 110 KNOTS. AFTER LANDFALL AROUND TAU 72, THE SYSTEM WILL WEAKEN BEFORE MOVING BACK OVER WATER AS A STRONG TYPHOON IN THE GULF OF TONKIN BEFORE MAKING A SECOND LANDFALL NEAR HAIPHONG, VIETNAM. AFTER LANDFALL, RAPID WEAKENING IS EXPECTED OVER THE RUGGED TERRAIN OF NORTHERN VIETNAM. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN FAIR AGREEMENT THROUGH TAU 72. CROSS-TRACK SPREAD BEGINS TO SHOW UP IN THE TRACKERS BY TAU 48, EXPANDING TO A 190NM SPREAD BY TAU 72, WITH THE GFS ON THE NORTH SIDE, AND ECMWF ON THE SOUTH. ALONG-TRACK SPREAD IS MODEST TO TAU 72, INCREASING AFTER TAU 48 TO A MAX OF 150NM BY TAU 72. THE JTWC FORECAST IS CONSISTENT WITH AND JUST NORTH OF THE MULTI-MODEL CONSENSUS MEAN. CROSS-TRACK SPREAD INCREASES TO NEARLY 400NM BY TAU 120, WITH THE GFS ENSEMBLE MEAN TAKING THE SYSTEM INTO SOUTHEASTERN CHINA, TO THE SOUTH OF HONG KONG, WHILE THE ECMWF MOVES THE SYSTEM INTO NORTHERN VIETNAM, NEAR VINH. ALONG-TRACK SPREAD INCREASES AS WELL, UP TO ABOUT 250NM BY THE END OF THE FORECAST PERIOD. THE JTWC FORECAST IS SLIGHTLY NORTH OF, AND SLIGHTLY FASTER THAN, THE CONSENSUS MEAN THROUGH THE EXTENDED FORECAST. INTENSITY GUIDANCE AGREEMENT IS IMPROVING, THOUGH THE BULK OF THE GUIDANCE DEPICTS A LOWER PEAK INTENSITY WITH THIS RUN, THE SOLE OUTLIER PEAKING ABOVE 100 KTS BEING THE HWRF, WHILE THE COAMPS-TC (BOTH VERSIONS) AND CTR1 ARE PEAKING NEAR 95 KTS. SOMEWHAT SURPRISINGLY, THIS RUN OF THE HAFS-A HAS DROPPED THE PEAK TO JUST 75 KTS, WHICH INTRODUCES A FAIR AMOUNT OF UNCERTAINTY INTO THE FORECAST INTENSITY. MULTIPLE LONG-RANGE RI AIDS ARE POPPING, INCLUDING THE FRIA AND RICN, THOUGH THE COAMPS-TC ENSEMBLE RI PROBABILITIES HAVE LOWERED TO ROUGHLY 60 PERCENT. THE JTWC FORECAST REMAINS ON THE AGGRESSIVE SIDE OF THE GUIDANCE PACKAGE, PARTICULARLY AFTER TAU 24. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN