Tropical Storm ROKE Advisory 10月1日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (ROKE) WARNING NR
011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 30.6N 142.5E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 315 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 18 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN
ASYMMETRIC CENTRAL DENSE OVERCAST, WITH A LOW LEVEL CIRCULATION
THAT HAS BECOME INCREASINGLY EXPOSED AS THE BULK OF THE CONVECTION
IS SHEARED NORTHEASTWARD ACROSS THE EASTERN SEMICIRCLE. AN EARLIER
301325Z GMI 89GHZ MICROWAVE IMAGE REVEALS CURVED CONVECTIVE BANDING
WRAPPING INTO A WELL DEFINED LOW LEVEL CIRCULATION. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EIR IMAGERY AS
WELL AS A PARTIAL 301111Z METOP-C ASCAT. THE INITIAL INTENSITY OF
55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A COMBINATION OF
PGTW AND RJTD DVORAK CURRENT INTENSITY ESTIMATES ALONG WITH
OBJECTIVE DVORAK ESTIMATES FROM CIMSS ADT AND SATCON.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: NORTHEAST PERIPHERY OF MID-LEVEL
SUBTROPICAL RIDGE (STR)
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T3.0 - 45 KTS
   RJTD: T3.5 - 55 KTS
   CIMSS SATCON: 66 KTS AT 301235Z
   CIMSS ADT: 79 KTS AT 301740Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 25-30 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: CURRENT ENVIRONMENTAL FACTORS ARE MARGINALLY
FAVORABLE CHARACTERIZED BY WARM (28-29C) SEA SURFACE (SSTS), STRONG
POLEWARD OUTFLOW, OFFSET BY HIGH (25-30KTS) VERTICAL WIND SHEAR. TS
20W IS CURRENTLY ACCELERATING NORTHEASTWARD AS THE SYSTEM TRANSITS
ALONG THE NORTHWEST PERIPHERY OF THE MID-LEVEL SUBTROPICAL RIDGE
(STR) TO THE SOUTHEAST. THE SYSTEM WILL CONTINUE TO TRANSIT
NORTHEASTWARD QUICKLY OVER THE NEXT 36 HOURS, DUE TO THE SYSTEM'S
POSITION WITHIN THE SUBTROPICAL WESTERLIES. AFTER WHICH, TS 20W'S
ACCELERATED TRACK MOTION IS FOLLOWED BY A SIGNIFICANT DECELERATION
AND SLOWED POLEWARD PROGRESSION, AS A LOW-LEVEL HIGH BUILDS IN TO
THE NORTH-NORTHWEST, THROUGH TAU 72. BY TAU 36, A SUBTROPICAL
SHORTWAVE TROUGH WILL INTERACT WITH THE SYSTEM, WHICH WILL BEGIN
INITIATING SUBTROPICAL TRANSITION, AND IS FORECAST TO COMPLETE
SUBTROPICAL TRANSITION BY TAU 72. AS THIS SUBTROPICAL TRANSITION
OCCURS THE SYSTEMS WIND FIELD WILL ALSO EXPAND INTO A MORE BROAD
GALE FORCE WIND FIELD. TY 20W IS EXPECTED TO MAINTAIN ITS CURRENT
INTENSITY BEFORE A STEADY WEAKENING TREND OCCURS AS THE SYSTEM
TRANSITS IN A MARGINALLY FAVORABLE ENVIRONMENT.
MODEL DISCUSSION: NUMERICAL MODELS ARE IN TIGHT AGREEMENT WITH A
GRADUAL CROSS TRACK SPREAD OF 130 NM BY TAU 72. THIS UNCERTAINLY IN
THE TRACK FORECAST IS DUE TO THE COMPLEX STEERING BEYOND TAU 36.
HOWEVER, THE 301200Z GFS ENSEMBLE (GEFS) AND 300600Z ECMWF ENSEMBLE
(EPS) BOTH AGREE ON THE NORTHEAST TRACK FORECAST ALONG WITH A
SLOWED STORM MOTION BY THE END OF THE FORECAST. THEREFORE, THERE IS
MEDIUM CONFIDENCE IN THE JTWC TRACK FORECAST THROUGH TAU 72. THERE
IS MEDIUM CONFIDENCE IN THE JTWC INTENSITY FORECAST AND FOLLOWS
CLOSE TO THE MULTI-MODEL CONSENSUS.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM//
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