Tropical Storm THIRTEEN Advisory 8月31日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (THIRTEEN)
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 20.1N 133.1E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 482 NM SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A FULLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC), DISPLACED TO THE
NORTHEAST OF DISORGANIZED FLARING CONVECTION. THE SYSTEM HAS
MODERATE NORTHERLY SHEAR EMANATING FROM STY 12W TO THE NORTH AND
IS STRUGGLING TO CONSOLIDATE. THE INITIAL POSITION IS ASSESSED WITH
HIGH CONFIDENCE BASED ON THE EXPOSED CIRCULATION. THE INITIAL
INTENSITY IS ASSESSED WITH LOW CONFIDENCE BASED ON TWO SHIP
OBSERVATIONS TO THE SOUTHEAST AND NORTHEAST NEAR NEAR 30 KNOTS, AND
A PARTIAL 301238Z ASCAT-B PASS WITH 25 KNOT WINDS IN THE SOUTHEAST
QUADRANT.
INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).
CURRENT STEERING MECHANISM: NORTHWEST SIDE OF A NEAR EQUATORIAL
RIDGE (NER) TO THE EAST.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: WEAK EQUATORWARD
   OTHER FACTORS: VWS FROM STY 12W
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: LOW
   INITIAL WIND RADII: NOT APPLICABLE
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.
FORECAST DISCUSSION: TD 13W IS FORECAST TO TRACK NORTH-NORTHWEST
ALONG THE WEST SIDE OF THE STEERING RIDGE TO THE EAST. THE SYSTEM
IS WITHIN 400NM OF STY 12W AND IS IN THE PROCESS OF BEING CAPTURED
IN A BINARY INTERACTION. THUS THE TRACK IS EXPECTED TO STEADY
APPROACH STY 12W IN A GRADUAL CYCLONIC ARC, ULTIMATELY MERGING WITH
THE BROADENING WIND FIELD ASSOCIATED WITH STY 12W AND DISSIPATING
AS A DISTINCT, SEPARATE CIRCULATION. THIS EVENTUALITY IS
ANTICIPATED NO LATER THAN TAU 48 AS THE SYSTEM SLIDES SOUTH OF
OKINAWA. HOWEVER, WHILE THE SYSTEM WILL DISSIPATE AS A SEPARATE
SYSTEM, THE WINDS WILL REMAIN HIGH WITH THE FORECAST INTENSITY
CURRENTLY FORECAST TO BE 35 KNOTS AS THE SYSTEM MERGES WITH STY
12W.
MODEL DISCUSSION: NUMERICAL GUIDANCE IS IN POOR AGREEMENT, WITH THE
GALWEM AND UKMET ENSEMBLE TAKING THE SYSTEM MORE SHARPLY WESTWARD
AND MERGING WITH STY 12W FASTER THAN THE REMAINDER OF THE GUIDANCE.
THE JTWC FORECAST LIES CLOSE TO THE GFS TRACKER, NORTH OF THE
CONSENSUS MEAN, WITH LOW CONFIDENCE DUE TO THE VAGARIES ASSOCIATED
WITH THE BINARY INTERACTION WITH STY 12W. INTENSITY GUIDANCE IS
EXTREMELY UNCERTAIN, WITH AVAILABLE GUIDANCE INDICATING A SPREAD
BETWEEN 25 KNOTS (DECAY SHIPS) AND 125 KNOTS (HWRF). OBVIOUSLY BOTH
OF THESE OUTLIERS ARE UNLIKELY, AND THE JTWC FORECAST IS HEDGED
ABOVE THE SHIPS GUIDANCE, BUT WELL BELOW THE CONSENSUS MEAN AFTER
TAU 36, WHEN IT DISPLAYS A STEEP CLIMB TO THE UNREALISTIC PEAKS OF
THE HWRF. NEEDLESS TO SAY, CONFIDENCE IS LOW IN THE FORECAST
INTENSITY.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   INTENSITY 0 - 72 HR: LOW//
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