WDPN33 PGTW 152100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 16W (NANMADOL) WARNING NR 013// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 23.4N 136.4E INITIAL INTENSITY: 85 KTS GEOGRAPHIC REFERENCE: 503 NM EAST-SOUTHEAST OF KADENA AB MOVEMENT PAST 6 HOURS: WESTWARD AT 07 KTS SIGNIFICANT WAVE HEIGHT: 32 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A TYPHOON WITH AN INNER CORE THAT IS STEADILY BECOMING MORE ORGANIZED. MULTIPLE CONVECTIVE BURSTS HAVE BEEN OCCURRING CONTINUOUSLY AROUND THE EYEWALL, AND THE EYE HAS BEGUN CLEARING OUT AND WARMING OVER THE PAST 3 HOURS. DEEP CONVECTION WITH CLOUD TOP TEMPERATURES COLDER THAN -80 DEGREES CELSIUS HAS EXTENDED AROUND 50 TO 75 PERCENT OF THE EYEWALL. A 151837Z GMI MICROWAVE PASS CONFIRMED A 75 PERCENT COMPLETE EYEWALL, OPEN IN THE NORTHEAST QUADRANT. STRONG EQUATORWARD UPPER-LEVEL OUTFLOW IS OBSERVED, AND ONLY WEAK ON THE POLEWARD SIDE DUE TO THE PRESENCE OF A SUBTROPICAL RIDGE OVER JAPAN. THE STORM APPEARS TO BE UNDERGOING A PERIOD OF RAPID INTENSIFICATION, WITH AGENCY AND AUTOMATED DVORAK ESTIMATES SUPPORTING AN INITIAL INTENSITY OF 85 KT, AN INCREASE OF 20 KT DURING THE PAST 12 HOURS. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE OVER JAPAN AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T5.0 - 90 KTS RJTD: T4.5 - 77 KTS KNES: T5.0 - 90 KTS CIMSS SATCON: 85 KTS AT 151626Z CIMSS ADT: 79 KTS AT 151740Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG EQUATORWARD 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: TYPHOON 16W (NANMADOL) APPEARS TO BE RAPIDLY INTENSIFYING, WITH AN EYE APPEARING IN SATELLITE IMAGERY AND A RELATIVELY COMPACT RADIUS OF MAXIMUM WINDS OF ABOUT 25 NM. THE ENVIRONMENT IS HIGHLY FAVORABLE, WITH WIND SHEAR UNDER 10 KT AND SEA SURFACE TEMPERATURES OF 29-30 DEGREES CELSIUS. THE SHIPS RAPID INTENSIFICATION PREDICTION AID (RIPA) INDICATES AN 81 PERCENT CHANCE OF 35 KT INTENSIFICATION DURING THE NEXT 24 HOURS, AND A 60 PERCENT CHANCE OF 40 KT. THE JTWC FORECAST THUS CALLS FOR RAPID INTENSIFICATION TO CONTINUE, WITH NANMADOL REACHING A PEAK INTENSITY OF 125 KT WITHIN 36 HOURS TO THE NORTHEAST OF THE ISLAND OF MINAMI DAITO JIMA. ENVIRONMENTAL CONDITIONS WILL REMAIN FAVORABLE THROUGH 48 HOURS, THOUGH THE TYPHOON IS FORECAST TO PASS OVER AN EDDY OF LOW OCEAN HEAT CONTENT SOUTHEAST OF AMAMI OSHIMA DURING THE 36-48 HOUR PERIOD, WHICH WILL LIKELY PUT A CEILING ON THE PEAK INTENSITY. ON THE JTWC FORECAST TRACK, NANMADOL WILL TRACK NORTHWESTWARD DURING THE NEXT 48 HOURS, PASSING WITHIN 75 NM EAST OF AMAMI OSHIMA AROUND 171800Z. A TURN NORTHWARD TOWARD KYUSHU AT A RELATIVELY SLOW SPEED OF 9 KT IS THEN EXPECTED AS THE TYPHOON CROSSES THE RYUKYU ISLANDS. THIS WILL BRING THE STORM OVER COOLER SEA SURFACE TEMPERATURES OF 27-28 DEGREES CELSIUS, AND A DRY AIR MASS DEPOSITED IN THE YELLOW SEA BY AN UPPER-LEVEL TROUGH OVER NORTHEASTERN CHINA MAY GET ENTRAINED INTO THE CIRCULATION DURING THE 48-72 HOUR PERIOD. COMBINED WITH INTERACTION WITH THE KYUSHU LAND MASS, THIS SHOULD INDUCE STEADY WEAKENING, AND NANMADOL IS FORECAST TO BE AROUND 90 KT INTENSITY ABOUT 70 NM SOUTH OF SASEBO, JAPAN BY 181800Z (TAU 72). AT THIS POINT, THERE IS GOOD MODEL AGREEMENT THAT THE TYPHOON WILL TURN NORTHEASTWARD ALONG HONSHU AS A SHORTWAVE TROUGH PASSES BY TO THE NORTH. HOWEVER, THERE IS SIGNIFICANT DISAGREEMENT ON THE TIMING OF THIS LEG OF THE TRACK, SINCE THE SHORTWAVE MAY MOVE EASTWARD QUICKLY, LEAVING A NEARLY ZONAL JET TO THE NORTH OF THE STORM, RESULTING IN WEAKER STEERING CURRENTS THAN ARE TYPICAL IN THIS REGION. ENSEMBLE GUIDANCE INDICATES THAT A STORM TRACKING FARTHER WEST OR ARRIVING NEAR KYUSHU LATER IS MORE LIKELY TO SLOW DOWN NEAR KYUSHU, AS THIS WOULD GIVE THE SHORTWAVE TO THE NORTH A GREATER CHANCE OF LEAVING THE TYPHOON BEHIND. THE JTWC FORECAST IS CLOSE TO A BLEND OF THE ECMWF, GFS, ECMWF ENSEMBLE MEAN, AND GFS ENSEMBLE MEAN, TAKING NANMODOL INTO HONSHU BY 96 HOURS CLOSE TO IWAKUNI, THEN CONTINUING INTO CENTRAL HONSHU BY 120 HOURS AT A MODERATE SPEED. THIS FORECAST IS 6-12 HOURS SLOWER THAN THE PREVIOUS ONE DURING THE 72-120 HOUR PERIOD. CONTINUING UNCERTAINTY IN THE TIMING OF THIS LEG MAKES TRACK FORECAST CONFIDENCE LOWER THAN AVERAGE AFTER 72 HOURS. REGARDLESS, NANMODOL IS EXPECTED TO WEAKEN STEADILY AS IT PASSES OVER KYUSHU AND HONSHU, RETAINING TYPHOON FORCE WINDS THROUGH 96 HOURS, THEN WEAKENING TO 45 KT OVER HONSHU AT THE END OF THE FORECAST PERIOD. BANDS OF ELEVATED WIND ARE EXPECTED TO OCCUR ON BOTH THE NORTHERN AND SOUTHERN COASTLINES OF HONSHU, AS A STRONG SUBTROPICAL RIDGE TO THE EAST WILL ENHANCE SOUTHERLIES ON THE SOUTHEASTERN SIDE OF THE STORM, AND A COLD SURGE OVER THE SEA OF JAPAN WILL ENHANCE NORTHERLIES ON THE NORTHWESTERN SIDE OF THE STORM. DUE TO THIS COLD SURGE AND ASSOCIATED FRONTAL ZONE, NANMODOL WILL BE UNDERGOING EXTRATROPICAL TRANSITION DURING THE 96-120 HOUR PERIOD. MODEL DISCUSSION: AS DISCUSSED ABOVE, ALONG-TRACK SPREAD IS LARGE DURING THE 72-120 HOUR PERIOD, AND THE JTWC FORECAST IS CLOSE TO A BLEND OF THE ECMWF, GFS, ECMWF ENSEMBLE MEAN, AND GFS ENSEMBLE MEAN. THE JTWC INTENSITY FORECAST IS ABOVE THE MULTI-MODEL CONSENSUS DUE TO THE EXPECTATION THAT RAPID INTENSIFICATION IS LIKELY DURING THE NEXT 24 HOURS. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN