Tropical Storm NANMADOL Advisory 9月16日

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//
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