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JTWC/18W/#05/08-20 06Z Prognostic Reasoning
WDPN32 PGTW 200900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W (EIGHTEEN)
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
INITIAL POSITION: 30.3N 127.9E
INITIAL INTENSITY: 30 KTS
GEOGRAPHIC REFERENCE: 191 NM SOUTH-SOUTHWEST OF SASEBO, JAPAN
MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 10 KTS
SIGNIFICANT WAVE HEIGHT: 12 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY-
EXPOSED LOW-LEVEL CIRCULATION (LLC), WITH FLARING DEEP CONVECTION.
THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON MSI.
THE INITIAL POSITION IS ALSO SUPPORTED BY THE 200708Z SSMIS 91GHZ
MICROWAVE IMAGE, WHICH REVEALS A DEFINED LLC POSITIONED JUST
SOUTHWEST OF A SMALL REGION OF DISORGANIZED DEEP CONVECTION. THE
INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON
RECENT ASCAT IMAGERY. ENVIRONMENTAL CONDITIONS ARE MARGINAL, WITH
FAIR OUTFLOW OFFSET BY DRY AIR ENTRAINMENT.
INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).
CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE (STR)
POSITIONED TO THE EAST AND SOUTHEAST, ORIENTED SSW TO NNE.
AGENCY DVORAK AND AUTOMATED FIXES:
PGTW: T2.5 - 35 KTS
RJTD: T1.5 - 25 KTS
KNES: T1.5 - 25 KTS
CIMSS SATCON: 39 KTS AT 200503Z
CIMSS ADT: 35 KTS AT 200530Z
CIMSS AIDT: 43 KTS AT 200530Z
CIMSS D-MINT: 23 KTS AT 200425Z
CIMSS D-PRINT: 29 KTS AT 200710Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
VWS: 5-10 KTS
SST: 28-29 CELSIUS
OUTFLOW: MODERATE EASTWARD
OTHER FACTORS: DRY AIR ENTRAINMENT
ANALYSIS CONFIDENCE:
INITIAL POSITION: MEDIUM
INITIAL INTENSITY: HIGH
INITIAL WIND RADII: NOT APPLICABLE
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 18W IS FORECAST TO
TRACK NORTH-NORTHEASTWARD TO NORTHEASTWARD THROUGH THE FORECAST
PERIOD AS IT ROUNDS THE NORTHWESTERN PERIPHERY OF THE STR. UPPER-
LEVEL CONDITIONS HAVE IMPROVED STEADILY OVER THE PAST DAY AS THE
SYSTEM TRACKED AWAY FROM AN UPPER-LEVEL LOW NEAR TAIWAN, WITH
IMPROVED EQUATORWARD OUTFLOW EVIDENT IN THE ANIMATED WATER VAPOR RGB
IMAGERY. ADDITIONALLY, EASTWARD OUTFLOW HAS MAINTAINED. HOWEVER, DRY
AIR ENTRAINMENT THROUGH THE COLUMN HAS CONTINUED TO HINDER ANY
SIGNIFICANT CONSOLIDATION. THERE IS A VERY SHORT WINDOW
FOR SLIGHT INTENSIFICATION TO 35 KNOTS OVER THE NEXT 12 HOURS UNTIL
VERTICAL WIND SHEAR INCREASES TO HIGH (25-40 KNOTS) LEVELS AND DRY
AIR OVERWHELMS THE SYSTEM.
MODEL DISCUSSION: JTWC TRACK CONFIDENCE IS MEDIUM, WITH INCREASING
UNCERTAINTY IN THE EXACT TRACK AFTER TAU 24. IN LARGE PART, THIS IS
DUE TO THE WEAK NATURE OF THE SYSTEM AS IT WEAKENS NEAR LANDFALL. THE
CURRENT SUITE OF DETERMINISTIC GUIDANCE SHOWS A SPREAD FROM WESTERN
CENTRAL KYUSHU TO NORTHERN KYUSHU, WITH JTWC'S TRACK FORECAST ALIGNED
CLOSER TO ECMI, EEMI AND AVNI. THE 191800Z ECMWF ENSEMBLE (ECENS) RUN
SHOWS THE BULK OF THE SOLUTIONS TRACKING THE SYSTEM INTO THE KOREAN
STRAIT AND NORTHERN KYUSHU. THE 200000Z GFS ENSEMBLE (GEFS) IS
SIMILAR, WITH A WIDER SPREAD OF SOLUTIONS FROM THE KOREAN STRAIT TO
SOUTHERN KYUSHU. OVERALL, BOTH ENSEMBLES INDICATE THAT A POTENTIAL
DIRECT TRACK OVER CHEJU-DO AND THE BUSAN AREA IS AT A VERY LOW
PROBABILITY. RELIABLE INTENSITY GUIDANCE INDICATES A PEAK INTENSITY
OF 30-35 KNOTS OVER THE NEXT 24 HOURS, WITH UNANIMOUS AGREEMENT ON A
SHARP WEAKENING TREND AFTER TAU 24. THE 191800Z COAMPS-TC (GFS
INITIAL BOUNDARY CONDITIONS) INTENSITY ENSEMBLE SHOWS SOME POTENTIAL
FOR THE SYSTEM TO REACH MINIMAL TROPICAL STORM STRENGTH PRIOR TO
LANDFALL, WITH A HIGH PROBABILITY OF TROPICAL DEPRESSION OR TROPICAL
DISTURBANCE INTENSITY AT LANDFALL AND BEYOND.
FORECAST CONFIDENCE:
TRACK 00-72 HR: MEDIUM
INTENSITY 00-72 HR: MEDIUM//
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楼主: yhh
发表于 2025-8-20 15:33
