WDPN31 PGTW 022100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (YAGI) WARNING NR 006// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 17.9N 120.9E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 198 NM NORTH OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 09 KTS SIGNIFICANT WAVE HEIGHT: 12 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL STORM (TS) 12W (YAGI) IS QUICKLY CROSSING THE NORTHERN PORTION OF LUZON, AND CURRENTLY RESIDES OVER THE NORTHERN PORTION OF THE CORDILLIERA CENTRAL MOUNTAIN RANGE. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RATHER SLOPPY STRUCTURE, MAKING DEFINITIVE POSITIONING A CHALLENGE. THE OUTER LOW-LEVEL BANDING FEATURES OVER THE WATER TO THE NORTH OF LUZON PROVIDE STRONG SUPPORT FOR A POSITION OVER NORTHERN LUZON, WHICH IS REFINED USING SURFACE OBSERVATIONS, PRIMARILY FROM LOAOG CITY, WHERE THE WINDS HAVE BACKED FROM SOUTH-SOUTHEASTERLY TO EAST-NORTHEASTERLY OVER THE PAST SIX HOURS, SUGGESTING THE LOW-LEVEL CIRCULATION CENTER (LLCC) LIES TO THE SOUTHEAST OF THE STATION. ADDITIONALLY, AN EARLIER 021251Z ASCAT-B PASS REVEALED THE DEVELOPMENT OF A SECONDARY LLCC JUST WEST OF THE LINGAYEN GULF, SETTING UP A LIKELY LEE-SIDE JUMP SCENARIO. ANIMATED WATER VAPOR IMAGERY DEPICTS AN UPPER-LEVEL ANTICYCLONE (ULAC) TO THE EAST OF TAIWAN AND A WEAK ULAC DIRECTLY ABOVE THE SYSTEM. THE INITIAL POSITION IS ASSESSED MEDIUM CONFIDENCE BASED ON THE DATA NOTED ABOVE. THE INITIAL INTENSITY IS ASSESSED WITH LOW CONFIDENCE, BASED PRIMARILY ON PERSISTENCE, SUPPORTED BY A DMINT ESTIMATE OF 30 KNOTS AND A DPRINT ESTIMATE OF 35 KNOTS. THE SYSTEM IS TRACKING GENERALLY NORTHWESTWARD ALONG THE SOUTHERN SIDE OF A STRONG SUBTROPICAL RIDGE (STR) OVER CHINA, MODIFIED BY THE PASSAGE OVER THE ROUGH TERRAIN AND THE INFLUENCE OF THE SECONDARY CIRCULATION CENTER TO THE SOUTHWEST. ANALYSIS REVEALS A MARGINALLY FAVORABLE ENVIRONMENT, WITH MODERATE EQUATORWARD AND POLEWARD OUTFLOW, AND LOW EASTERLY SHEAR OFFSET BY THE TERRAIN INFLUENCES AND LACK OF AN ENERGY SOURCE OVER LAND. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER STR OVER CHINA. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: NO CURRENT ESTIMATE RJTD: T2.0 - 30 KTS CIMSS DPRINT: 35 KTS AT 121800Z CIMSS DMINT: 32 KTS AT 121730Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 5-10 KTS SST: OVER LAND OUTFLOW: MODERATE POLEWARD AND EQUATORWARD OTHER FACTORS: LACK OF AN ENERGY SOURCE OVER LAND; TERRAIN INFLUENCE. ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: LOW INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: WHILE IN GENERAL, THE OVERALL TRACK SCENARIO IS STRAIGHT-FORWARD, THE NEAR-TERM TRACK FORECAST IS COMPLICATED BY THE LIKELIHOOD OF A LEE-SIDE JUMP SCENARIO, WHICH WILL HAVE A MAJOR IMPACT IN THE SHORT-TERM FORECAST. THE LATEST ANIMATED SHORTWAVE INFRARED (SWIR) IMAGERY AND THE MOST RECENT SURFACE OBSERVATIONS FROM LAOAG SUGGESTS THE LLCC MAY ALREADY BE ON THE COAST, OR VERY CLOSE TO IT, JUST SOUTHEAST OF LAOAG CITY. THE SWIR IN GENERAL BACKS THIS UP, AND ALSO SHOWS SCATTERED, BUT STILL DISORGANIZED, DEEP CONVECTIVE CELLS FLARING UP OVER WATER TO THE WEST AND THE SOUTHWEST. THE EARLIER ASCAT SHOWED A CLEAR-CUT LLCC JUST WEST OF LINGAYEN GULF, AND THE HIGH-RESOLUTION MODELS SHOW THIS MOVING QUICKLY NORTHWARD AND UNDERGOING BINARY INTERACTION WITH THE LLCC ASSOCIATED WITH 12W. THE NET EFFECT OF THIS BINARY INTERACTION WILL BE SOME POTENTIALLY ERRATIC, LOOPING MOTION, AND A SLOW DOWN OF THE TRACK SPEED, BEFORE THE TWO CIRCULATION CENTERS ULTIMATE MERGE. ONCE MERGER IS COMPLETED, EXPECTED BY TAU 24, THE SYSTEM IS EXPECTED TO THEN ACCELERATE OFF TO THE WEST AS THE STR TAKES OVER AS THE PREDOMINANT STEERING INFLUENCE. BY TAU 72, MODELS BEGIN TO DIVERGE FAIRLY STRONGLY, WITH THE ECMWF AND GFS MARKING THE OUTLIER POSITIONS, AS THEY DISAGREE ON THE MOVEMENT OF THE STR OVER CHINA. GFS MOVES IT EASTWARD, ALLOWING TS 12W TO TRACK ON A MORE WEST-NORTHWESTWARD TRACK AFTER TAU 72, WHILE THE ECMWF INITIALLY TRACKS THE STR EASTWARD LIKE GFS, ONLY TO TURN BACK TO THE WEST THEREAFTER, KEEPING TS 12W ON A MORE WEST OR SLIGHTLY WEST-SOUTHWEST TRACK THROUGH TAU 120. THE FORECAST HEDGES TOWARDS THE GFS, TAKING THE SYSTEM INTO NORTHEASTERN HAINAN BY TAU 96, THEN TO NEAR HAIPHONG, VIETNAM BY THE END OF THE FORECAST PERIOD. IN TERMS OF INTENSITY, IN THE NEAR-TERM, THE SYSTEM WILL INTENSIFY SLIGHTLY AS IT EMERGES BACK OVER WATER AND UNDERGOES A MERGER WITH THE SECONDARY CIRCULATION TO THE SOUTH AND COMPLETES THE LEE-SIDE JUMP. AFTER COMPLETION OF THE MERGER, THE SYSTEM IS EXPECTED TO INTENSIFY AT A FASTER RATE AS THE VORTEX CONSOLIDATES AND A STRONG ULAC DEVELOPS OVER TOP OF THE SYSTEM. PASSAGE OVER A POOL OF HIGH OHC AND DEVELOPMENT OF ENHANCED EASTWARD OUTFLOW INTO A TUTT-CELL TO THE NORTHEAST WILL ALLOW FOR A PERIOD OF RAPID INTENSIFICATION (RI) BETWEEN TAU 48 AND TAU 72, WITH A PEAK OF AT LEAST 110 KNOTS ANTICIPATED BY TAU 72. ONCE THE SYSTEM MAKES LANDFALL IT IS EXPECTED TO RAPIDLY WEAKEN DUE TO TERRAIN INTERACTIONS, DOWN TO APPROXIMATELY 90 KNOTS. WHILE THE FORECAST CALLS FOR A STEADILY WEAKENING STORM PRIOR TO LANDFALL IN VIETNAM, AND NOT CURRENTLY SHOWN IN THE MODEL DATA, IF THE SYSTEM REMAINS OVER WATER IN THE GULF OF TONKIN PRIOR TO THE SECOND LANDFALL IN VIETNAM, IT MAY REINTENSIFY OR AT MINIMUM MAINTAIN INTENSITY. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN FAIRLY GOOD AGREEMENT THROUGH TAU 72, WITH A ROUGHLY 100NM CROSS-TRACK SPREAD BETWEEN THE CONSENSUS MEMBERS. ALONG-TRACK SPREAD IS ALREADY AN ISSUE AS EARLY AS TAU 48, WITH THE GFS IN PARTICULAR BEING MUCH SLOWER THAN THE ECMWF AND THE UKMET, LEADING TO A 180NM ALONG-TRACK SPREAD BY TAU 72. THE JTWC FORECAST TO TAU 72 IS CONSISTENT WITH THE CONSENSUS MEAN, HEDGED MORE TOWARDS THE ECMWF IN TERMS OF TRACK SPEED. CROSS-TRACK SPREAD INCREASES SHARPLY AFTER TAU 72, WITH THE GFS ENSEMBLE MEAN AND ECMWF DETERMINISTIC MARKING THE OUTLIERS OF A NEARLY 400NM SPREAD. THE ECMWF TAKES THE SYSTEM ACROSS THE SOUTHERN PORTION OF HAINAN AND INTO NORTHERN VIETNAM AT ROUGHLY THE SAME LATITUDE. MEANWHILE THE GFS ENSEMBLE MEAN TAKES THE SYSTEM INTO SOUTHEAST CHINA. THE REMAINDER OF THE GUIDANCE PACKAGE IS GROUPED ROUGHLY ABOUT THE CONSENSUS MEAN. ALONG-TRACK SPREAD ALSO INCREASES SHARPLY, WITH THE UKMET FAR OUTRACING ALL OTHER GUIDANCE, GENERATING A 480NM SPREAD BY TAU 120. THE JTWC EXTENDED FORECAST HEDGES TOWARDS THE GFS TRACK AND LIES JUST NORTH OF THE CONSENSUS MEAN. ECMWF ENSEMBLE GUIDANCE IS IN BETTER AGREEMENT THAN THE GFS, WITH THE GFS SHOWING A VERY WIDE SPREAD WITH INCONGRUENT TRACKS INTO THE STRONG RIDGE OVER CHINA. INTENSITY GUIDANCE IS IN AGREEMENT ON A STEADY INTENSIFICATION TREND, WITH A ROUGHLY 50 KNOT SPREAD IN PEAK INTENSITIES. THE JTWC FORECAST LIES ON THE HIGHER END OF THE GUIDANCE PACKAGE, CLOSE TO THE HWRF AND COTC AND CTCX MEMBERS. ADDITIONALLY, THE LATEST COAMPS-TC ENSEMBLE INTENSIFICATION PROBABILITIES SHOW A 95 PERCENT CHANCE OF RI BETWEEN TAU 48 AND TAU 72, LENDING INCREASED CONFIDENCE TO THE INTENSITY FORECAST. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN