Tropical Storm HINNAMNOR Advisory 8月29日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (HINNAMNOR) WARNING
NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 27.2N 146.9E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 251 NM EAST OF CHICHI JIMA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A COMPACT
SYSTEM WITH A MORE CONSOLIDATED SPIRAL BANDING WRAPPING IN FROM EAST
THROUGH NORTHWEST INTO AN OBSCURED LOW LEVEL CIRCULATION CENTER
(LLCC). THE CENTRAL DENSE OVERCAST FEATURE, WHICH IS OBSCURING THE
LLCC, HAS DEEPENED AND PRODUCED A FORMATIVE EYE. THE INITIAL POSITION
IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE FORMATIVE EYE IN THE
EIR LOOP, ADJUSTED FOR A SLIGHT SOUTHEASTWARD TILT. THE INITIAL
INTENSITY OF 50KTS IS ASSESSED WITH MEDIUM CONFIDENCE AND HELD HIGHER
THAN AGENCY DVORAK ESTIMATES AND MORE IN LINE WITH THE AUTOMATED
DVORAK ESTIMATES TO REFLECT THE 6-HR EIR STRUCTURAL IMPROVEMENT AND
CONSISTENT WITH A FORMATIVE EYE. THE ENVIRONMENT REMAINS FAVORABLE
WITH STRONG EQUATORWARD OUTFLOW, LOW TO MEDIUM VERTICAL WIND SHEAR,
AND WARM (30-31C) SST VALUES.
INITIAL WIND RADII BASIS: PERSISTENCE.
CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
EXTENSION TO THE NORTH.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.5 - 35 KTS
   CIMSS SATCON: 48 KTS AT 281229Z
   CIMSS ADT: 47 KTS AT 281740Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TS HINNAMNOR WILL TRACK GENERALLY WESTWARD
TOWARD OKINAWA UNDER THE STEERING STR. AFTER TAU 72, A SECONDARY STR
OVER CENTRAL CHINA, EMERGING BEHIND A TRANSITORY SHORTWAVE TROUGH,
AND A NEAR EQUATORIAL RIDGE TO THE SOUTHEAST WILL COMPETE FOR
STEERING, FORCING THE SYSTEM TO BECOME QUASI-STATIONARY (QS) IN A COL
AREA. THE AFOREMENTIONED FAVORABLE CONDITIONS WILL PROMOTE GRADUAL
THEN RAPID INTENSIFICATION TO A PEAK OF 115KTS BY TAU 72. AFTERWARD,
COOLING SST DUE TO UPWELLING INDUCED BY THE SYSTEM BEING QS IN THE
COL WILL SLIGHTLY WEAKEN THE SYSTEM TO 105KTS BY TAU 120.
MODEL DISCUSSION: THE MAJORITY OF AVAILABLE NUMERICAL MODELS IS IN
BROAD AGREEMENT UP TO TAU 72. AFTERWARD, TWO MODELS - NVGM AND
UKMET - RECURVE THE VORTEX TOWARD JAPAN IN RESPONSE TO THE TRANSITORY
SHORTWAVE TROUGH. THE MAIN PACK CONTINUES WESTWARD TOWARD THE COL
AREA. IN VIEW OF THIS, AND GIVEN THE UNCERTAINTIES IN TRACK MOTION
INHERENT IN A COL, THERE IS MEDIUM CONFIDENCE IN THE JTWC TRACK, LAID
NEAR THE CONSENSUS OF THE MAIN PACK, AND INTENSITY FORECASTS UP TO
TAU 72 THEN LOW CONFIDENCE AFTERWARD.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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