Tropical Storm NORU Advisory 9月25日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 18W (NORU)
WARNING NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 15.1N 124.7E
   INITIAL INTENSITY: 135 KTS
   GEOGRAPHIC REFERENCE: 217 NM EAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
SUPER TYPHOON (STY) 18W HAS UNDERGONE EXTREME RAPID INTENSIFICATION
(ERI) FROM 45 KNOTS AT 231800Z TO THE CURRENT INTENSITY OF 135
KNOTS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
NEAR SYMMETRIC CENTRAL DENSE OVERCAST WITH A SMALL, OBLONG EYE
(5-8NM DIAMETER) WITH SPIRAL BANDING. OVER THE PAST FEW HOURS, EIR
INDICATES TROCHOIDAL MOTION AS THE SYSTEM TURNS GRADUALLY WESTWARD
AND TRACKS TOWARD DINGALAN BAY. IN GENERAL, STY 18W HAS MAINTAINED
A WARM EYE WITH THE EYE TEMPERATURE VARYING FROM 8.7C TO 16.0C (THE
241950Z EYE TEMPERATURE IS 11.9C) WITH DVORAK DATA-T ESTIMATES
RANGING FROM DT6.5 TO DT7.0 (127 TO 140 KNOTS) SINCE ABOUT 241730Z.
THE DVORAK FINAL-T ESTIMATES (BELOW) ARE CONSERVATIVE AND HELD
LOWER DUE TO CONSTRAINTS. ADT CURRENT INTENSITY ESTIMATES ARE ALSO
CONSERVATIVE WHILE RAW-T NUMBERS HAVE VARIED FROM 6.8 TO 7.0 (135
TO 140 KNOTS). THE INITIAL INTENSITY IS ASSESSED ABOVE THE FINAL-T
ESTIMATES BASED ON MULTIPLE, VERY CONSISTENT DVORAK DATA-T
ESTIMATES AS WELL AS THE ADT RAW-T VALUES, HOWEVER, THERE IS SOME
UNCERTAINTY IN THE EXACT INTENSITY THUS MEDIUM OVERALL CONFIDENCE.
ENVIRONMENTAL CONDITIONS ARE HIGHLY FAVORABLE WITH RADIAL OUTFLOW,
LOW VERTICAL WIND SHEAR, WARM SST VALUES AND HIGH OCEAN HEAT
CONTENT.
INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK
CURRENT STEERING MECHANISM: THE SYSTEM IS TRACKING ALONG THE
SOUTHERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) ENTRENCHED TO THE
NORTH.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T5.5 - 102 KTS
   RJTD: T5.5 - 102 KTS
   KNES: T6.0 - 115 KTS
   CIMSS SATCON: 95 KTS AT 241700Z
   CIMSS ADT: 107 KTS AT 241910Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE MAJOR CHANGES TO THE
INTENSITY FORECAST DUE TO THE ERI PHASE OVER THE PAST 24 HOURS.
FORECAST DISCUSSION: STY 18W BEARS MANY SIMILARITIES TO STY GONI
(2020), WHICH UNDERWENT ERI WHILE TURNING WEST-SOUTHWESTWARD TOWARD
SOUTHERN LUZON, HOWEVER, STY GONI ATTAINED STY STRENGTH TWO DAYS
PRIOR TO LANDFALL SO PEAKED MUCH HIGHER. STY 18W IS FORECAST TO
TRACK WESTWARD AND MAKE LANDFALL IN ABOUT 15 TO 18 HOURS WITH A
PEAK INTENSITY OF 145 KNOTS EXPECTED AT TAU 12. AFTER MAKING
LANDFALL, STY 18W WILL WEAKEN RAPIDLY AS IT CROSSES THE PHILIPPINE
ISLANDS, DOWN TO ABOUT 100 KNOTS BY TAU 36. MORE SIGNIFICANT
WEAKENING IS POSSIBLE. AFTER RE-EMERGING OVER THE SOUTH CHINA SEA,
STY 18W IS FORECAST TO RE-INTENSIFY TO A PEAK INTENSITY OF 115
KNOTS JUST PRIOR TO LANDFALL OVER CENTRAL VIETNAM NEAR TAU 72.
ENVIRONMENTAL CONDITIONS ARE EXPECTED TO REMAIN FAVORABLE ALTHOUGH
VERTICAL WIND SHEAR IS EXPECTED TO GRADUALLY INCREASE TO 15-20
KNOTS BY LANDFALL.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN GOOD
AGREEMENT WITH A 30-40NM SPREAD IN SOLUTIONS THROUGH TAU 18, AND AN
80-90NM SPREAD IN SOLUTIONS THROUGH THE REMAINDER OF THE FORECAST
THUS OVERALL HIGH CONFIDENCE IN THE JTWC FORECAST TRACK. DUE TO THE
POTENTIAL FOR MORE SIGNIFICANT WEAKENING OVER THE PHILIPPINE
ISLANDS AND POTENTIAL FOR RAPID INTENSIFICATION OVER THE SOUTH
CHINA SEA, THERE IS LOW CONFIDENCE IN THE JTWC INTENSITY FORECAST.
RELIABLE INTENSITY GUIDANCE INDICATES A STEEP DROP IN INTENSITY AS
THE SYSTEM TRACKS OVER LAND WITH A RANGE OF 55 (HWRF) TO 85
(COAMPS-TC) KNOTS WITH RE-INTENSIFICATION TO 90-115 KNOTS. THE
241200Z COAMPS-TC ENSEMBLE INDICATES A 40 TO 60 PERCENT PROBABILITY
OF RAPID INTENSIFICATION IN THE TAU 48 TO TAU 60 TIMEFRAME.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: HIGH
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: MEDIUM//
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