WDPN31 PGTW 032100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (YAGI) WARNING NR 010// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.8N 118.3E INITIAL INTENSITY: 55 KTS GEOGRAPHIC REFERENCE: 296 NM NORTH-NORTHWEST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: WESTWARD AT 06 KTS SIGNIFICANT WAVE HEIGHT: 21 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL STORM (TS) 12W (YAGI) CONTINUES TO STEADILY CONSOLIDATE AFTER HAVING MOVED OUT OVER THE OPEN WATERS OF THE SOUTH CHINA SEA (SCS). ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS DISORGANIZED FLARING CONVECTION, PRIMARILY LIMITED TO THE SOUTHERN AND EASTERN PORTIONS OF THE CIRCULATION. A 031528Z GMI 37GHZ MICROWAVE IMAGE SHOWED THAT THE LOW LEVEL CIRCULATION CENTER (LLCC) IS WELL-DEFINED, WITH AN ENCLOSED CYAN RING SURROUNDING THE CENTER. HOWEVER, CONVECTION IS LIMITED ON THE NORTHWEST SIDE, INDICATIVE OF A STUBBORN REGION OF MID-LEVEL DRY AIR, WHICH IS ALSO CAPTURED IN CROSS-SECTIONS OF BOTH THE HAFS-A AND HWRF MODELS. THE PRESENCE OF THIS DRY AIR IS ALSO PROVED BY THE FACT THAT WHAT CONVECTION DOES TRY TO FORM IN THE NORTHWESTERN QUADRANT CANNOT PERSIST. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON AN EXTRAPOLATION OF THE WELL-DEFINED MIC EYE FEATURE IN THE MICROWAVE IMAGE NOTED ABOVE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, HEDGED SLIGHTLY LOWER THAN THE T4.0 ESTIMATES FROM KNES AND PGTW, AND MORE IN LINE WITH THE OBJECTIVE INTENSITY ESTIMATES NOTED BELOW, SPECIFICALLY THE RAW ADT OF T3.5, AND THE CIMSS DPRINT AND DMINT ESTIMATES. THE SYSTEM IS IN A VERY FAVORABLE ENVIRONMENT, WITH LOW VWS, VERY WARM SSTS, HIGH OHC AND MODERATE EQUATORWARD OUTFLOW. THE ONLY LIMITING FACTORS AT PRESENT IS THE PERSISTENT WEDGE OF DRY AIR AND THE STILL DISORGANIZED NATURE OF THE VORTEX, BOTH OF WHICH ARE EXPECTED TO IMPROVE IN THE NEAR-TERM. ALL THINGS CONSIDERED, THE STAGE IS SET FOR TS YAGI TO PUT ON A SHOW IN THE NEXT COUPLE OF DAYS. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) OVER CHINA. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.0 - 65 KTS RJTD: T3.5 - 55 KTS RCTP: T3.5 - 55 KTS KNES: T4.0 - 65 KTS CIMSS SATCON: 49 KTS AT 031800Z CIMSS ADT: 45 KTS AT 031800Z CIMSS DPRINT: 57 KTS AT 031800Z CIMSS DMINT: 55 KTS AT 031712Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE VWS: 5-10 KTS SST: 31-32 CELSIUS OUTFLOW: MODERATE EQUATORWARD OTHER FACTORS: DRY MID-LEVEL AIR IN THE NORTHWEST QUADRANT. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH 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: FOLLOWING A SHORT PERIOD OF ERRATIC MOTION OVER THE PAST 12 HOURS AS THE LOW-LEVEL VORTEX CONSOLIDATED, THE SYSTEM HAS STEADIED UP ON A WEST-NORTHWESTWARD TRACK ALONG THE SOUTHERN SIDE OF A STRONG STR OVER CHINA. TS 12W WILL CONTINUE TO TRACK WESTWARD THROUGH TAU 48, BEFORE SHIFTING TO A MORE WEST-NORTHWESTWARD TRACK THROUGH TAU 120, AS THE RIDGE SHIFTS EAST TO NEAR SHANGHAI. THE CURRENT FORECAST TAKES THE SYSTEM OVER THE EXTREME NORTHEASTERN TIP OF HAINAN ISLAND AROUND TAU 60, THEN QUICKLY TRANSIT THE HAINAN STRAIT AND MOVE INTO THE NORTHERN PORTION OF THE GULF OF TONKIN BY TAU 72. A SECOND LANDFALL IS EXPECTED NEAR HAIPHONG, VIETNAM AROUND TAU 84, AFTER WHICH THE SYSTEM WILL QUICKLY MOVE INLAND TO NEAR THE LAOTIAN BORDER BY THE END OF THE FORECAST PERIOD. IN TERMS OF INTENSITY, THE STAGE IS SET FOR THE SYSTEM TO RAPIDLY INTENSIFY, ONCE THE LOW-LEVEL VORTEX ALIGNS AND THE DRY AIR CURRENTLY LURKING IN THE NORTHWESTERN QUADRANT DISAPPEARS. BOTH OF THESE ARE EXPECTED TO OCCUR WITHIN THE NEXT 12 TO 18 HOURS. IN THE NEAR-TERM, THE DRY AIR AND VORTEX ASYMMETRIES WILL KEEP A LID ON INTENSIFICATION, WITH THE FORECAST CALLING FOR MODEST INTENSIFICATION TO 65 KNOTS BY TAU 12. BUT THEN THE GLOVES COME OFF AND THE SYSTEM WILL EMBARK ON A PERIOD OF RAPID INTENSIFICATION (RI). BETWEEN TAU 24 AND 48, THE SYSTEM PASSES OVER A POOL OF HIGH OHC WATERS, DEVELOPS AN UPPER-LEVEL ANTICYCLONE (ULAC) OVER TOP OF THE LLCC, AND TAPS INTO A STRONG EQUATORWARD OUTFLOW CHANNEL AROUND TAU 36. THESE FACTORS WILL FUEL AN IMPRESSIVE RI EVENT, WITH THE SYSTEM FORECAST TO REACH A PEAK OF AT LEAST 115 KNOTS BY TAU 48. TS 12W IS LIKELY TO MAINTAIN INTENSITY THROUGH LANDFALL AS IT BECOMES SELF-SUSTAINING, WITH RADIAL OUTFLOW ALOFT, AND MINIMAL SHEAR, ALONG WITH STEADY SSTS. TERRAIN INTERACTION WILL WEAKEN THE SYSTEM AS IT CROSSES THROUGH THE HAINAN STRAIT, BUT IT IS STILL EXPECTED TO BE A STRONG TYPHOON UPON ENTERING THE GULF OF TONKIN. WHILE NOT CAPTURED IN THE FORECAST DIRECTLY, THE EXTREMELY HIGH OHC OF THE GULF OF TONKIN (EXCEEDING 120 KJ PER CM2), ACCOMPANIED BY STRONG EQUATORWARD AND WESTWARD OUTFLOW ALOFT AND LOW SHEAR WILL LIKELY SUPPORT A REINTENSIFICATION OF THE SYSTEM, ESPECIALLY IF THE ULTIMATE TRACK MINIMIZES TERRAIN INFLUENCES FROM HAINAN. THE POTENTIAL FOR A SIGNIFICANT TYPHOON WITH AN INTENSITY AT OR ABOVE 100 KNOTS MAKING LANDFALL IN NORTHERN VIETNAM IS A DISTINCT POSSIBILITY. AFTER MAKING THE SECOND LANDFALL, THE SYSTEM WILL RAPIDLY WEAKEN AND DISSIPATE OVER LAND BY THE END OF THE FORECAST PERIOD. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE CONTINUES TO COME INTO BETTER AGREEMENT WITH EACH SUCCESSIVE RUN. CROSS-TRACK SPREAD IS NOW DOWN TO 95NM AT TAU 72, THOUGH ALL BUT THE GALWEM ARE ACTUALLY CONTAINED IN A MUCH SMALLER 50NM ENVELOPE. ALONG-TRACK SPREAD AT TAU 72 IS ACTUALLY THE BIGGER ISSUE, WITH THE GFS LAGGING 130NM BEHIND THE VERY FAST UKMET TRACKERS. CROSS-TRACK SPREAD OPENS UP TO 180NM BY TAU 120, BUT ALONG-TRACK SPREAD INCREASES SHARPLY AS THE ECMWF AND GALWEM MODELS RACE THE SYSTEM INTO THAILAND WHILE THE GFS AND GFS ENSEMBLE KEEP THE CENTER OVER NORTHERN VIETNAM. THE JTWC FORECAST LIES ALONG THE NORTHERN SIDE OF THE GUIDANCE ENVELOPE AND A BIT FASTER THAN THE CONSENSUS MEAN THROUGH TAU 72. THE FORECAST REMAINS ON THE NORTHERN SIDE OF THE GUIDANCE ENVELOPE THROUGH TAU 120. CONFIDENCE IS HIGH THROUGH TAU 72, TRENDING TO MEDIUM IN THE EXTENDED RANGE IN LIGHT OF THE LARGE ALONG-TRACK SPREAD. INTENSITY GUIDANCE IS IN GOOD AGREEMENT, WITH THE BULK OF THE GUIDANCE SHOWING THE SYSTEM RAPIDLY INTENSIFYING TO A PEAK BETWEEN 95-110 KNOTS. NEARLY EVERY RI AID IS BEING TRIGGERED WITH THIS RUN, WITH EXTREMELY HIGH PROBABILITIES EXCEEDING 70 PERCENT FOR MANY OF THEM. ADDITIONALLY, THE COAMPS-TC ENSEMBLE RI PROBABILITIES ARE EXCEEDING 80 PERCENT, PROVIDING HIGH CONFIDENCE TO THE JTWC INTENSITY FORECAST THROUGH TAU 72. CONFIDENCE IN THE INTENSITY FORECAST IS LOWER AFTER TAU 72, IN LIGHT OF THE POTENTIAL FOR REINTENSIFICATION IN THE GULF OF TONKIN, WHICH IS NOT CAPTURED BY ANY DETERMINISTIC MODEL GUIDANCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: HIGH INTENSITY 0 - 72 HR: HIGH INTENSITY 72-120 HR: MEDIUM// NNNN