Tropical Storm NORU Advisory 9月24日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (NORU)
WARNING NR 008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 17.2N 129.3E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 504 NM EAST-NORTHEAST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
CENTRAL COLD COVER (CCC) WITH A SYMMETRIC REGION OF COLD
UPPER-LEVEL CLOUDS OBSCURING THE LOW-LEVEL CIRCULATION CENTER,
WHICH IS TUCKED UNDER THE NORTHERN EDGE OF THE CCC. A RECENTLY
RECEIVED 231708Z AMSR2 89GHZ COLOR COMPOSITE MICROWAVE IMAGE
REVEALS TIGHTLY-WRAPPED LOW-LEVEL BANDING WRAPPING INTO A
WELL-DEFINED CENTER WITH CURVED CONVECTIVE BANDING OVER THE
SOUTHERN SEMICIRCLE. BASED ON THIS IMAGE, THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE AND IS ABOUT 18NM TOO FAR NORTH. CCC
INDICATES ARRESTED DEVELOPMENT THUS THE INITIAL INTENSITY IS HELD
AT 45 KTS WITH MEDIUM CONFIDENCE. THE AFOREMENTIONED 231708Z AMSR2
WINDSPEED IMAGE INDICATED PEAK WINDS OF 35 KNOTS OVER THE SOUTH
QUADRANT, WHICH FALLS WITHIN THE RANGE OF DVORAK INTENSITY ESTIMATES.
ENVIRONMENTAL CONDITIONS ARE FAVORABLE WITH MODERATE WESTWARD
OUTFLOW, ENHANCED BY AN UPPER-LOW OVER THE SOUTH CHINA SEA, AND LOW
VERTICAL WIND SHEAR (VWS).
INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK
CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF THE DEEP-LAYERED
SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTH.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 40 KTS AT 231718Z
   CIMSS ADT: 35 KTS AT 231750Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TS 18W IS FORECAST TO TRACK WEST-SOUTHWESTWARD
ALONG THE SOUTHWEST PERIPHERY OF THE STR THROUGH TAU 24 THEN TURN
MORE WESTWARD AS IT APPROACHES LUZON WITH LANDFALL NEAR TAU 36. DUE
TO THE FAVORABLE CONDITIONS, END OF THE CCC (ARRESTED DEVELOPMENT)
STAGE AND DECREASE IN VWS OVER THE PAST 12 HOURS, TS 18W IS
EXPECTED TO INTENSIFY QUICKLY PRIOR TO LANDFALL TO AN INTENSITY OF
65 TO 70 KNOTS. AFTER TRANSITING ACROSS LUZON, TS 18W WILL
RE-EMERGE OVER THE SOUTH CHINA SEA AND WILL COMMENCE A
RE-INTENSIFICATION PHASE AS IT TRACKS WESTWARD TOWARD AND OVER
VIETNAM AND SOUTHEAST ASIA. PEAK INTENSITY IS EXPECTED BETWEEN TAU
72 AND TAU 96, WHEN LANDFALL OCCURS. RAPID WEAKENING WILL OCCUR AS
THE SYSTEM TRACKS INLAND.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH THE FORECAST PERIOD WITH A 70NM TO 110NM SPREAD IN
SOLUTIONS FROM TAU 72 TO TAU 96 LENDING HIGH CONFIDENCE TO THE JTWC
FORECAST TRACK. RAPID INTENSIFICATION IS POSSIBLE PRIOR TO LANDFALL
WITH THE TRIGGERING OF RAPID INTENSIFICATION (RI) GUIDANCE AND UP
TO 85 PERCENT PROBABILITY OF RI INDICATED IN THE 231200Z COAMPS-TC
ENSEMBLE GUIDANCE. COAMPS-TC ALSO SHOWS A 20 TO 50 PERCENT
PROBABILITY OF RI IN THE SOUTH CHINA SEA, WHICH IS LIKELY DURING
THE 251800Z TO 270600Z PERIOD. HWRF INDICATES A PEAK OF 90 KNOTS AT
TAU 84 (270600Z) AS WELL.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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