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JTWC/18W/#01/08-18 06Z Prognostic Reasoning
WDPN32 PGTW 190900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W (EIGHTEEN)
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
INITIAL POSITION: 27.1N 127.6E
INITIAL INTENSITY: 30 KTS
GEOGRAPHIC REFERENCE: 376 NM SOUTH-SOUTHWEST OF SASEBO, JAPAN
MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 12 KTS
SIGNIFICANT WAVE HEIGHT: 16 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
AS DEPICTED IN ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI), A
DISTINCT CLOSED LOW-LEVEL CIRCULATION (LLC) HAS FORMED OVER THE
PAST SIX HOURS, WITH LOW-LEVEL CLOUD LINES WRAPPING INTO THE CENTER
AND IMPROVED DEEP CONVECTIVE BANDING. ANIMATED RADAR IMAGERY SUPPORTS
THE INITIAL POSITION WITH HIGH CONFIDENCE, REVEALING EXTENSIVE
CONVECTIVE BANDING OVER THE EASTERN SEMICIRCLE WRAPPING INTO THE
NORTHWEST QUADRANT OF THE LLC. ANIMATED WATER VAPOR IMAGERY SHOWS
EXPANDING POLEWARD VENTING OVER THE NORTHERN AND EASTERN QUADRANTS,
WITH CONVERGENT UPPER-LEVEL FLOW PERSISTING OVER THE SOUTHWESTERN
SEMICIRCLE ASSOCIATED WITH A QUASISTATIONARY UPPER-LEVEL LOW CENTERED
JUST EAST OF TAIWAN. EXTENSIVE DRY AIR IS PRESENT OVER THE
SOUTHWESTERN QUADRANT OF THE SYSTEM LIMITING CONVECTIVE DEVELOPMENT
OVER THIS REGION. SURFACE OBSERVATIONS FROM KADENA AIR BASE INDICATE
SOUTHWESTERLY WINDS AT 10-15 KNOTS, WITH SLP NEAR 1009MB. MAXIMUM
WINDS OBSERVED THUS FAR ARE FROM YORONJIMA (27.0N 128.4E), WHICH
REPORTED ABOUT 22 KNOTS SUSTAINED (1-MINUTE AVERAGE). RECENT ASCAT
IMAGERY INDICATED A SWATH OF 25-30 KNOT WINDS OVER THE EASTERN
SEMICIRCLE, WHICH SUPPORTS THE INITIAL INTENSITY ESTIMATE OF 30
KNOTS.
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.
AGENCY DVORAK AND AUTOMATED FIXES:
PGTW: T1.5 - 25 KTS
KNES: T1.5 - 25 KTS
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
VWS: 0-5 KTS
SST: 29-30 CELSIUS
OUTFLOW: MODERATE EASTWARD
OTHER FACTORS: DRY AIR ENTRAINMENT
ANALYSIS CONFIDENCE:
INITIAL POSITION: HIGH
INITIAL INTENSITY: HIGH
INITIAL WIND RADII: NOT APPLICABLE
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.
FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 18W WILL TRACK
GENERALLY NORTHWARD THROUGH TAU 48 ALONG THE WESTERN PERIPHERY OF
THE STR. MODEST INTENSIFICATION TO A PEAK INTENSITY OF 35 KNOTS IS
ANTICIPATED AS THE CORE MOISTENS BRIEFLY AND THE SYSTEM MOVES AWAY
FROM THE UPPER-LEVEL LOW NEAR TAIWAN. AFTER TAU 48, TD 18W WILL
RECURVE AROUND THE NORTHWESTERN PERIPHERY OF THE STR AND WEAKEN
QUICKLY DUE TO INCREASING EASTERLY FLOW AND HIGH (40-45 KNOTS)
VERTICAL WIND SHEAR ASSOCIATED WITH A STRONG HIGH SITUATED OVER THE
KOREAN PENINSULA. ADDITIONALLY, EXTENSIVE DRY AIR WILL PREVAIL ACROSS
THE KOREAN STRAIT AND WESTERN JAPAN, WHICH WILL LEAD TO DISSIPATION
BY TAU 72.
MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN TIGHT AGREEMENT
THROUGH TAU 24, WITH A 40NM CROSS-TRACK SPREAD AT TAU 24. AFTER TAU
24, GUIDANCE DIVERGES WITH EEMI AND AEMI SHOWING TWO EXTREME,
UNLIKELY SOLUTIONS. THE REMAINDER OF THE GUIDANCE IS SPREAD FROM
SOUTHERN SOUTH KOREA TO NORTHERN KYUSHU. THE GEFS AND ECENS ENSEMBLES
ALSO REVEAL A LARGE SPREAD OF SOLUTIONS SUPPORTING THE JTWC FORECAST
TRACK WITH MEDIUM CONFIDENCE. AS MENTIONED, ENVIRONMENTAL CONDITIONS
ARE NOT OPTIMAL THUS RELIABLE INTENSITY GUIDANCE GENERALLY PEAKS AT
35-40 KNOTS NEAR TAU 48, WITH STEADY WEAKENING THROUGH TAU 72.
FORECAST CONFIDENCE:
TRACK 00-72 HR: MEDIUM
INTENSITY 00-72 HR: MEDIUM//
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楼主: yhh
发表于 2025-8-19 15:09
