WDPN33 PGTW 010300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 20W (KRATHON) WARNING NR 016// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 20.6N 119.6E INITIAL INTENSITY: 130 KTS GEOGRAPHIC REFERENCE: 290 NM SOUTH-SOUTHWEST OF TAIPEI, TAIWAN MOVEMENT PAST 6 HOURS: WESTWARD AT 04 KTS SIGNIFICANT WAVE HEIGHT: 53 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY INDICATES THAT THE CLOUD TOP TEMPERATURES OF SUPER TYPHOON (STY) 20W (KRATHON) HAVE WARMED ABOUT 10C OVER THE PAST SIX HOURS, AND HAVE DRAMATICALLY REDUCED IN AREAL EXTENT, PARTICULARLY ON THE NORTHERN SIDE. AT THE SAME TIME THE EYE HAS WARMED AND CLEARED OUT, WITH EYE TEMPERATURES NOW UP TO 12C. SO WHILE THE STORM LOOKS MORE IMPRESSIVE IN THE MSI AND EIR, IT LOOKS TO HAVE STARTED A SLOW WEAKENING TREND. ANIMATED RADAR IMAGERY FROM TAIWAN SHOWS THE DEVELOPMENT OF THE FIRST PHASE OF AN EYEWALL REPLACEMENT CYCLE (ERC), WITH A BAND OF DEEP CONVECTION SEPARATED FROM THE INNER CORE BY A MOAT, ON THE EASTERN SIDE OF THE CIRCULATION. ADDITIONALLY, A 302026Z SSMIS COLOR ENHANCED MICROWAVE IMAGE DEPICTED A TEXTBOOK STATIONARY BANDING COMPLEX (SBC) ACROSS THE SOUTHERN PERIPHERY OF THE SYSTEM, WRAPPING UP INTO A DEVELOPING SECONDARY EYEWALL ON THE EAST SIDE. THE SYSTEM HAS BEEN MOVING QUITE SLOWLY OVER THE PAST 12 HOURS AND IS LIKELY STARTING TO UPWELL COOLER WATERS, WHICH WILL ROB THE SYSTEM OF ITS ENERGY SOURCE GOING FORWARD. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON ANALYSIS OF THE ANIMATED RADAR DATA, THE 16NM EYE IN THE VISIBLE IMAGERY AND EXTRAPOLATION OF A 302201Z SENTINEL-1A SAR PASS. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE CONGRUENCE OF AGENCY DVORAK CURRENT INTENSITY ESTIMATES, HEDGED LOWER BASED ON THE SAR DATA NOTED ABOVE, WHICH INDICATED A MUCH WEAKER WIND FIELD OF JUST 110-115 KNOTS AND MORE IN LINE WITH THE AVAILABLE OBJECTIVE ESTIMATES NOTED BELOW. THE ENVIRONMENT IS STEADILY BECOMING MORE MARGINAL DUE TO THE COMBINED NEGATIVE EFFECTS OF COOL WATER UPWELLING, THE ONSET OF AN ERC INCREASING MID-LEVEL NORTHERLY SHEAR AND TERRAIN INFLUENCES. INITIAL WIND RADII BASIS: SAR DATA CURRENT STEERING MECHANISM: WEAK STEERING PATTERN WITH A STR TO THE EAST AND A SECOND RIDGE OVER SOUTHERN CHINA TO THE WEST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T7.0 - 140 KTS RJTD: T7.0 - 140 KTS KNES: T6.5 - 127 KTS DEMS: T7.0 - 140 KTS CIMSS SATCON: 124 KTS AT 010130Z CIMSS ADT: 134 KTS AT 302330Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 28-29 CELSIUS OUTFLOW: STRONG RADIAL ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THE FORECAST IS ONCE AGAIN SLOWED SIGNIFICANTLY IN THE EXTENDED RANGE, DUE TO THE EXTREMELY HIGH UNCERTAINTY IN THE FORECAST MODEL DATA. FORECAST DISCUSSION: SUPER TYPHOON (STY) 20W HAS LIKELY PEAKED AND HAS ALREADY STARTED A SLOW WEAKENING TREND BASED ON THE ANIMATED EIR IMAGERY, WHILE IT MOVES SLOWLY WESTWARD. THE SYSTEM IS ENSCONCED IN A COMPETING STEERING PATTERN, WITH THE RIDGE TO THE EAST AND TO THE WEST VYING FOR DOMINANCE. THE EASTERN RIDGE IS EXPECTED TO BUILD, WHILE MOVING NORTHWESTWARD OVER THE NEXT 24 HOURS, WHICH SHOULD PUSH 20W FIRST TO THE NORTH OVER THE NEXT 12 HOURS OR SO. AFTER TAU 24, THE RIDGE STARTS TO MOVE TO THE NORTHEAST, WHILE REORIENTING TO A NORTHEAST-SOUTHWEST ORIENTATION. COMBINED WITH THE PASSAGE OF AN UPPER-LEVEL TROUGH OVER THE YELLOW SEA, THIS WILL ALLOW STY 20W TO TURN NORTHEASTWARD, MAKE LANDFALL ALONG THE SOUTHWESTERN TAIWAN COAST AROUND TAU 48, THEN CROSS THE ISLAND. A LEE-SIDE JUMP IS ANTICIPATED BY TAU 72, WITH THE LLCC REFORMING ON THE NORTHEASTERN SIDE OF TAIWAN. HOWEVER, WHATEVER REMNANTS THAT DO EMERGE BACK OVER WATER WILL NOT LAST LONG, AS HIGH SHEAR AND AN INFLUX OF DRY AIR WILL INHIBIT INTENSIFICATION THROUGH THE END OF THE FORECAST PERIOD. THE ERC APPEARS TO HAVE BEGUN BUT THE EXACT TIMING OF FULL ONSET, THE AMOUNT OF WEAKENING AND THE DURATION OF THE CYCLE ARE UNKNOWN, COMPLICATED BY THE FACT THAT THE SYSTEM IS EXPECTED TO REMAIN SLOW-MOVING, AND CONTINUE UPWELLING OF COOLER WATERS, WHICH IS LIKELY TO SUPPORT AN INCOMPLETE ERC. AS THE SYSTEM MOVES CLOSER TO TAIWAN, THE INFLUENCE OF THE COMPLEX TERRAIN WILL ONLY ADD TO THE WEAKENING OF THE SYSTEM. ONCE ASHORE, STY 20W WILL RAPIDLY WEAKEN AS IT CROSSES THE HIGH TERRAIN OF THE CENTRAL MOUNTAIN RANGE. AFTER MOVING BACK OVER WATER, THE SYSTEM WILL CONTINUE TO WEAKEN UNDER THE INFLUENCE OF INCREASING SHEAR AND DRY AIR ENTRAINMENT. THE ABOVE IS ESSENTIALLY THE SCENARIO OUTLINED BY THE ECMWF. AN ALTERNATIVE SCENARIO, PRIMARILY DEPICTED BY THE GFS, SHOWS THE POLAR OPPOSITE TRACK. IN THE GFS SOLUTION, THE COMPETING RIDGING PATTERN REMAINS FIRMLY IN PLACE FOR THE THROUGH TAU 72, SUCH THAT THE SYSTEM MOVES VERY LITTLE DURING THAT TIMEFRAME. AFTER TAU 72, THE SIGNIFICANTLY WEAKER SYSTEM, THEN TRACKS WEST-SOUTHWEST ALONG THE LOW- TO MID-LEVEL FLOW, TRACKING JUST SOUTH OF HONG KONG THROUGH TAU 120.IN THE ALTERNATE SCENARIO, THE SYSTEM WEAKENS DOWN TO A TROPICAL STORM DUE TO ERC AND INCREASING SHEAR, BEFORE DISSIPATING TO THE SOUTHWEST OF HONG KONG. MODEL DISCUSSION: IN THE AGGREGATE, TRACK GUIDANCE REMAINS IN VERY POOR AGREEMENT, GENERATING EXTREME UNCERTAINTY IN THE FORECAST TRACK. IN THE NEAR-TERM HOWEVER, THE BULK OF THE GUIDANCE IS IN MARGINALLY GOOD AGREEMENT, WITH ALL BUT THE GFS SHOWING THE SYSTEM SLOWING ARCING ONTO A NORTHEASTWARD TRACK BY TAU 36, THEN MAKING LANDFALL BY TAU 48 AND CONTINUING ON TO CROSS THE ISLAND UP THROUGH TAU 72. AFTER THIS POINT, THE NAVGEM DISSIPATES THE SYSTEM OVER TAIWAN, THE GALWEM AND UKMET TAKE THE SYSTEM INTO THE ECS, WHILE THE ECMWF BECOMES QUASI-STATIONARY JUST NORTHEAST OF TAIWAN. THE ENSEMBLE MEANS ALSO SHOW A HIGH DEGREE OF UNCERTAINTY WITH THE GEFS TURNING THE SYSTEM WESTWARD AT TAU 72 FROM CENTRAL TAIWAN, WHILE THE ECEPS MEAN MOVES THE SYSTEM INTO CHINA SOUTH OF SHANGHAI BY TAU 120. THEN THERE IS THE GFS WHICH AS DESCRIBED ABOVE, DOES ITS OWN THING. THE RESULT IS A DEGREE OF SPREAD THAT IS COMPLETELY UNREPRESENTATIVE OF THE OVERALL SITUATION. THE JTWC FORECAST REMAINS GENERALLY CONSISTENT WITH THE PREVIOUS FORECAST, BUT SLOWS DOWN SIGNIFICANTLY AS A HEDGE AGAINST THE ALTERNATE SCENARIO DESCRIBED ABOVE BUT OTHERWISE HAS NOT CHANGED SIGNIFICANTLY. INTENSITY GUIDANCE IS ALSO HIGHLY UNCERTAIN, BOTH IN THE NEAR- AND LONG-TERM DUE TO NEAR-TERM IMPACTS OF THE ERC AND THE LONG-TERM IMPACTS OF WHICH TRACK IS ULTIMATELY TAKEN. NEEDLESS TO SAY, CONFIDENCE IS LOW FOR ALL FORECAST PARAMETERS. FORECAST CONFIDENCE: TRACK 0 - 72 HR: LOW TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: LOW INTENSITY 72-120 HR: LOW// NNNN