Tropical Storm NAMTHEUN Advisory 10月15日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (NAMTHEUN) WARNING
NR
020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 25.1N 159.0E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 278 NM EAST-NORTHEAST OF MINAMI TORI SHIMA
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
MEDIUM-SIZED SYSTEM WITH PERSISTENT DEEP CONVECTION SLIGHTLY
DISJOINTED TO THE NORTH AND EAST OF THE MAIN LOW-LEVEL CIRCULATION
(LLC). THE INITIAL POSITION IS EXTRAPOLATED WITH MEDIUM CONFIDENCE
BASED ON A 141726Z SSMIS 91GHZ MICROWAVE IMAGE. THE INITIAL
INTENSITY OF 35KTS IS PLACED WITH MEDIUM CONFIDENCE BASED ON AN
OVERALL ASSESSMENT OF MULTIPLE AGENCIES, AUTOMATED DVORAK ESTIMATES
(ADT), AND SATELLITE CONSENSUS (SATCON). ANALYSIS INDICATES A
MARGINALLY FAVORABLE ENVIRONMENT WITH MODERATE RADIAL OUTFLOW AND
WARM SST OFFSET BY MODERATE TO STRONG VWS AND SUBSIDENCE ALONG THE
NORTHEASTERN PERIPHERY DUE TO AN UPPER LEVEL LOW TO THE NORTHEAST
OF TS 23W. TS 23W IS TRACKING ON THE POLEWARD SIDE OF THE STR
TO THE SOUTH.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE SOUTH.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.0 - 30 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 49 KTS AT 142010Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL
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 23W WILL CONTINUE ON ITS CURRENT TRACK
UP TO TAU 36. AFTERWARD, A SECONDARY STR TO THE EAST WILL ASSUME
STEERING AND DRIVE THE SYSTEM NORTHWARD, THEN ACCELERATE IT
NORTHEASTWARD AFTER TAU 60. THE MARGINALLY FAVORABLE ENVIRONMENT
WILL FUEL A SLIGHT INTENSIFICATION TO 40KTS AND SUSTAIN IT UP TO
TAU 36. AFTERWARD, INCREASING VWS AND COOLING SSTS WILL GRADUALLY
ERODE THE SYSTEM DOWN TO 30KTS BY TAU 96. CONCURRENTLY, TS 23W
GAINS SUBTROPICAL CHARACTERISTICS, THEN AROUND TAU 72 TS 23W WILL
BEGIN EXTRA-TROPICAL TRANSITION (ETT) AS IT APPROACHES THE
BAROCLINIC ZONE. BETWEEN TAU 96 AND 120, TS 23W WILL BECOME A
MODERATE GALE-FORCE COLD-CORE LOW, COMPLETING ETT BY TAU 120.
MODEL DISCUSSION: NUMERICAL MODELS ARE IN VERY TIGHT AGREEMENT ONCE
NAVGEM IS EXCLUDED FROM THE MULTIPLE MODEL CONSENSUS WITH ONLY A
105NM SPREAD AT TAU 72. HOWEVER, INCLUDING NAVGEM, THE SPREAD
INCREASES TO 320NM AT ITS WIDEST, LENDING MEDIUM CONFIDENCE AT TAU
72, THEN LOW CONFIDENCE AFTERWARD DUE TO UNCERTAINTIES IN THE STORM
SPEED DURING ETT. THERE IS ALSO MEDIUM CONFIDENCE THE INTENSITY
FORECAST UP TO TAU 72 AND LOW CONFIDENCE AFTERWARD.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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