Tropical Storm MERBOK Advisory 9月12日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (FIFTEEN)
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 21.5N 161.0E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 341 NM WEST-NORTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
UPPER-LEVEL CONDITIONS ARE COMPLEX: AN ANTICYCLONE IS CENTERED NEAR
18N 159E WITH A NARROW TUTT POSITIONED ALONG THE NORTHERN PERIPHERY
OF THE SYSTEM WHICH IS PRODUCING VIGOROUS WEST-SOUTHWESTERLY FLOW
OVER THE NORTHERN HALF OF THE SYSTEM. STRONG DIFFLUENCE OVER THE
SOUTHERN HALF OF THE SYSTEM IS MAINTAINING PERSISTENT CURVED
CONVECTIVE BANDING BUT LIMITING OVERALL DEVELOPMENT. ADDITIONALLY,
ROBUST POLEWARD OUTFLOW INTO THE TUTT CELL TO THE NORTH IS
IMPROVING QUICKLY. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY DEPICTS FRAGMENTED BANDING WITH A CLUSTER OF FLARING
CONVECTION OVER THE EASTERN QUADRANT. AN 111715Z SSMIS 91GHZ COLOR
COMPOSITE MICROWAVE IMAGE REVEALS SHALLOW BANDING WRAPPING INTO A
DEFINED, EXPOSED LOW-LEVEL CIRCULATION CENTER WITH CONVECTIVE
BANDING CONFINED TO THE SOUTHERN SEMICIRCLE. THE INITIAL POSITION
IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE SSMIS IMAGE. THE
INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE PGTW DVORAK ESTIMATE AND RECENT ASCAT DATA.
INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK
CURRENT STEERING MECHANISM: STEERING IS CURRENTLY TRANSITIONING
FROM THE NEAR-EQUATORIAL RIDGE TO THE SOUTHEAST TO THE NORTH-SOUTH
ORIENTED STR POSITIONED TO THE EAST
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.5 - 35 KTS
   RJTD: T1.5 - 25 KTS
   CIMSS ADT: 32 KTS AT 111730Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
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: AS FORECAST WELL BY THE NUMERICAL MODELS, THE
STR HAS RE-ALIGNED IN A MORE NORTH-SOUTH CONFIGURATION WITH A
STRONG TUTT CELL POSITIONED TO THE NORTH NEAR 31N 165E.
CONSEQUENTLY, TS 15W IS BEGINNING TO TURN MORE POLEWARD AND IS
FORECAST TO TRACK NORTHWARD THROUGH TAU 60 THEN NORTH-NORTHEASTWARD
THROUGH TAU 72 AS IT BEGINS TO APPROACH THE STR AXIS. TS 15W IS
EXPECTED TO INTENSIFY SLOWLY THROUGH TAU 24 UNDER MARGINALLY-
FAVORABLE CONDITIONS THEN AT A FASTER RATE OF INTENSIFICATION
AFTER TAU 24 AS VERTICAL WIND SHEAR DECREASES TO LOW LEVELS AIDED
BY STRONG POLEWARD OUTFLOW. THE PEAK INTENSITY OF 85 KNOTS IS
EXPECTED TO OCCUR NEAR TAU 72. NEAR TAU 72, SST WILL
GRADUALLY COOL WITH EXTRA-TROPICAL TRANSITION (ETT) EXPECTED TO
COMMENCE AS THE SYSTEM BEGINS TO INTERACT WITH THE MIDLATITUDE
WESTERLIES AND BAROCLINIC ZONE. TS 15W WILL COMPLETE ETT BY TAU 96 AS
IT GAINS FRONTAL CHARACTERISTICS AND ACCELERATES NORTHEASTWARD WITHIN
THE STRONG MIDLATITUDE SOUTHWESTERLY FLOW.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 72 WITH A 100NM SPREAD IN SOLUTIONS AT TAU 72. THE
111200Z ECMWF ENSEMBLE (EPS) AND GFS ENSEMBLE (GEFS) ARE ALSO IN
TIGHT AGREEMENT LENDING HIGH CONFIDENCE TO THE JTWC FORECAST TRACK.
AFTER TAU 72, THE DETERMINISTIC GUIDANCE DIVERGES, MAINLY
ALONG-TRACK, WITH A SIGNIFICANT DIFFERENCE IN TRACK SPEEDS THUS LOW
CONFIDENCE. RELIABLE INTENSITY GUIDANCE IS IN FAIR AGREEMENT AND
INDICATES RAPID INTENSIFICATION (RI): COAMPS-TC (GFS VERSION)
INDICATES RI WITH A PEAK INTENSITY OF 110 KNOTS AT TAU 48 WHILE
HWRF INDICATES RI AND A PEAK INTENSITY OF 100 KNOTS AT TAU 72.
WHILE RI IS CERTAINLY LIKELY AFTER TAU 24, IT IS NOT LIKELY TO
BEGIN NOW DUE TO THE MARGINALLY-FAVORABLE UPPER-LEVEL CONDITIONS
THUS THE JTWC FORECAST IS SET AT A LOWER PEAK OF 85 KNOTS AT TAU
72. THE COAMPS-TC ENSEMBLE INDICATES A 70 TO 100 PERCENT
PROBABILITY OF RI IN THE TAU 12 TO TAU 40 TIMEFRAME.
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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