WDPN33 PGTW 272100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (TWENTY) WARNING NR 007// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 17.5N 164.1E INITIAL INTENSITY: 55 KTS GEOGRAPHIC REFERENCE: 179 NM SOUTHWEST OF WAKE ISLAND MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 08 KTS SIGNIFICANT WAVE HEIGHT: 20 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN EXTREMELY COMPACT SYSTEM, WITH PERSISTENT DEEP CONVECTION CONTINUING TO DEVELOP IN AND AROUND THE ASSESSED LOW LEVEL CIRCULATION CENTER (LLCC). A DISTINCT, IF VERY SMALL, MICROWAVE EYE FEATURE WAS OBSERVED IN BOTH A 271415Z AMSR3 AND 271438Z AMSR2 COLOR-ENHANCED 37GHZ MICROWAVE IMAGES. DEEP CONVECTION AT THAT TIME WAS DISPLACED TO THE NORTHERN FLANK OF THE LLCC, AND THIS ORIENTATION IS ASSUMED TO REMAIN IN PLACE IN LIGHT OF THE PERSISTENCE OF LIGHT SOUTHERLY SHEAR. UPPER- LEVEL ANALYSIS SHOWS THE SYSTEM POSITIONED JUST WEST OF A 200MB ANTICYCLONE, WHICH IS PROVIDING FOR BOTH LOW DEEP-LAYER SHEAR AND STRONG POLEWARD OUTFLOW ALOFT, HELPING TO SUSTAIN THE REMARKABLE BURST IN INTENSIFICATION SEEN OVER THE PAST 12 HOURS. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN EXTRAPOLATION OF THE MICROWAVE EYE FEATURE SEEN IN THE MICROWAVE IMAGERY DISCUSSED ABOVE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE AS WELL. THE BULK OF BOTH THE OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES ARE STRUGGLING TO ACCURATELY ESTIMATE THE INTENSITY DUE TO THE EXTREMELY COMPACT STRUCTURE. THE RAW ADT OF T3.6 IS MOST LIKELY CLOSEST TO REALITY BASED ON PERSISTENCE WITH THE SAR DATA FROM LAST NIGHT WHICH SHOWED 50-55 KNOT WINDS ALREADY AT THAT POINT. ENVIRONMENTAL CONDITIONS ARE FAVORABLE TO HIGHLY FAVORABLE, WITH LOW SHEAR, ROBUST OUTFLOW ALOFT, WARM SSTS AND IN ADDITION, THE SYSTEM IS CROSSING OVER A PATCH OF VERY HIGH OHC WATERS WITH VALUES EXCEEDING 120 KJ PER CM2. INITIAL WIND RADII BASIS: PERSISTENCE WITH EARLIER SAR AND SCATTEROMETER DATA. CURRENT STEERING MECHANISM: NORTHERN FLANK OF A DEEP-LAYER RIDGE COMPLEX WHICH EXTENDS FROM SOUTH OF GUAM NORTHEAST TO A POSITION EAST OF TS 21W. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T1.5 - 25 KTS KNES: T2.5 - 35 KTS PHFO: T2.5 - 35 KTS CIMSS SATCON: 45 KTS AT 271435Z CIMSS ADT: 51 KTS AT 271730Z CIMSS AIDT: 42 KTS AT 271730Z CIMSS D-MINT: 33 KTS AT 271436Z CIMSS D-PRINT: 36 KTS AT 271800Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG POLEWARD OTHER FACTORS: EXTREMELY COMPACT SIZE OF THE CIRCULATION. ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THE FORECAST HAS BEEN EXTENDED TO 120 HOURS AND THE MAXIMUM INTENSITY HAS INCREASED SIGNIFICANTLY. FORECAST DISCUSSION: TROPICAL STORM (TS) 20W (TWENTY) HAS PUT ON QUITE THE SHOW OVER THE PAST 12 HOURS, UNEXPECTEDLY UNDERGOING RAPID INTENSIFICATION, FROM 30 KNOTS TO 55 KNOTS PRESENTLY. THE SYSTEM IS TRACKING EAST-NORTHEASTWARD ALONG THE NORTHERN FLANK OF A BROAD REGION OF TROFING WHICH EXTENDS FROM SOUTH OF GUAM ALL THE WAY UP THE EASTERN SIDE OF BOTH TS 2OW AND TS 21W FURTHER TO THE NORTHEAST. OVER THE NEXT 24 TO 36 HOURS, THE NORTHEASTERN PORTION OF THIS RIDGE WILL BUILD AND COME TO DOMINATE THE STEERING FOR TS 20W THROUGH TAU 60. AFTER TAU 60, TWO FACTORS COME INTO PLAY TO MAKE THE TRACK MORE UNCERTAIN. FIRST AND FOREMOST, TS 20W WILL BEGIN DIRECT BINARY INTERACTION WITH TS 21W AND COMMENCE A FUJIWHARA MOTION, WHILE SIMULTANEOUSLY THE TWO SYSTEMS TOGETHER MOVE INTO A GENERALLY WEAK STEERING PATTERN. THE FORECAST CALLS FOR TS 20W TO TRACK NORTHWARD FROM TAU 36 TO TAU 60, THEN TURN NORTHWESTWARD AS TS 21W TRACKS BY TO THE SOUTHWEST. THE CURRENT FORECAST CALLS FOR TS 20W TO UNDERGO A BRIEF FUJIWHARA WITH 21W BEFORE BEING EJECTED TO THE NORTHEAST BY TAU 120, THOUGH THE EXTENT OF THE FUJIWHARA IS HIGHLY UNCERTAIN AT THIS POINT IN TIME AND THE SYSTEMS COULD UNDERGO A MUCH STRONGER INTERACTION. WHILE UNDERGOING BINARY INTERACTION, TS 20W WILL ALSO BEGIN SUBTROPICAL TRANSITION (STT) BY TAU 96. REGARDING INTENSITY, THE SYSTEM HAS CLEARLY OUTPERFORMED NEARLY ALL GUIDANCE AND EXPECTATIONS. HIGHLY FAVORABLE ENVIRONMENTAL CONDITIONS ARE EXPECTED TO PERSIST FOR THE NEXT 36 HOURS, AND WILL ALLOW FOR 20W TO CONTINUE RAPIDLY INTENSIFYING UP TO AT LEAST 85 KNOTS BEFORE INCREASING SHEAR AND DRY AIR ENTRAINMENT WILL CONSPIRE TO WEAKEN THE SYSTEM THROUGH THE REMAINDER OF THE FORECAST PERIOD. MODEL DISCUSSION: TRACK GUIDANCE IS HIGHLY UNCERTAIN, ESPECIALLY AFTER TAU 60. CROSS-TRACK SPREAD INCREASES TO NEARLY 1000NM BY TAU 120, BETWEEN THE NAVGEM AND GALWEM WHICH TRACK THE SYSTEM SLOWLY WESTWARD AFTER TAU 72 AND THE GEFS MEAN WHICH RAPIDLY TRACKS THE SYSTEM NORTHEASTWARD IN THE MID-LATITUDE WESTERLIES. THE AI MODELS, AS WELL AS THE GFS ARE CLUSTERED ON THE EASTERN FLANK OF THE GUIDANCE ENVELOPE, WHILE THE CONSENSUS, ECENS AND MOGREPS ARE POSITIONED DOWN THE MIDDLE. THE JTWC FORECAST IS PLACED NEAR THE AI CONSENSUS MEAN, ON THE EASTERN EDGE OF THE ENVELOPE, WITH LOW CONFIDENCE. INTENSITY GUIDANCE ALSO DISPLAYS A LARGE AMOUNT OF UNCERTAINTY. NEARLY EVERY RAPID INTENSIFICATION (RI) AID HAS TRIGGERED, AND ONLY THE SHIPS- NAVGEM AND GFS DEPICT AN INTENSITY BELOW 80 KNOTS. THE JTWC FORECAST IS PLACED NEAR THE NON-RI INFLUENCED CONSENSUS MEAN THROUGH TAU 36 WITH LOW CONFIDENCE, AND IN LIGHT OF THE VAST NUMBER OF RI AIDS TRIGGERING, IT IS NOT OUT OF THE REALM OF POSSIBILITY THAT THE SYSTEM COULD REACH 100 KNOTS OR MORE WITHIN THE NEXT 36 HOURS. HOWEVER, AFTER TAU 36, ALL MODELS INDICATE RAPID AND STEADY WEAKENING THROUGH THE REMAINDER OF THE FORECAST PERIOD. FORECAST CONFIDENCE: TRACK 00-72 HR: LOW TRACK 72-120 HR: LOW INTENSITY 00-72 HR: LOW INTENSITY 72-120 HR: LOW// NNNN