WDPN32 PGTW 210300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (EIGHTEEN) WARNING 
NR 008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 32.0N 129.2E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 71 NM SOUTH-SOUTHWEST OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM 18W WITH CURVED CONVECTIVE BANDING WRAPPING INTO A COMPACT,
OBSCURED LOW-LEVEL CIRCULATION CENTER (LLCC). ANIMATED WATER VAPOR
IMAGERY SHOWS DEFINED CIRRUS FILAMENTS EXTENDING EASTWARD AND
EQUATORWARD FROM THE SYSTEM, INDICATIVE OF STRONG OUTFLOW ON THOSE
DIRECTIONS. ENVIRONMENTAL ANALYSIS INDICATES THAT 18W IS IN A
FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG OUTFLOW ALOFT, LOW TO
MODERATE (15-20 KTS) NORTHERLY VERTICAL WIND SHEAR, AND WARM (29-30
C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH
MEDIUM CONFIDENCE BASED ON LOW-LEVEL CLOUD TRACING IN THE ANIMATED
MSI. THE INITIAL INTENSITY OF 40 KTS IS ALSO ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE LISTED AGENCY DVORAK FIXES AND OBJECTIVE
INTENSITY ESTIMATES RANGING FROM 35-45 KTS.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A SUBTROPICAL
RIDGE POSITIONED TO THE SOUTH-SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   CIMSS ADT: 45 KTS AT 210000Z
   CIMSS AIDT: 45 KTS AT 210000Z
   CIMSS D-PRINT: 37 KTS AT 210000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

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: 18W IS FORECAST TO TRACK EAST-NORTHEASTWARD,
ALONG THE NORTHERN PERIPHERY OF THE SUBTROPICAL RIDGE TO THE SOUTH
THROUGHOUT THE FORECAST PERIOD. THE LANDFALL LOCATION HAS SHIFTED
SLIGHTLY SOUTH COMPARED TO THE PREVIOUS FORECAST AND IS NOW
FORECAST TO OCCUR CLOSE TO NAGASHIMA ISLAND NEAR TAU 12. REGARDING
INTENSITY, 18W IS FORECAST TO WEAKEN AFTER MAKING LANDFALL DUE TO
TERRAIN INTERACTION. ADDITIONALLY, AFTER TAU 12, VERTICAL WIND
SHEAR WILL SIGNIFICANTLY INCREASE AS A RIDGE BUILDS IN OVER KOREA
AND BRINGS IN ENHANCED EASTERLY UPPER-LEVEL WINDS (40-45 KTS)
DIRECTLY OVER THE TOP OF THE VORTEX. AS A RESULT, DISSIPATION IS
EXPECTED TO OCCUR NO LATER THAN TAU 48, SOUTH OF SHIKOKU.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN MODERATE
AGREEMENT WITH THE PRIMARY OUTLIERS BEING THE ECMWF ENSEMBLE MEAN
AND JGSM ENSEMBLE MEAN, WHICH BOTH HAVE THE SYSTEM LOOPING
UNREALISTICALLY BACK WEST OF KYUSHU. OTHERWISE, MODELS GENERALLY
AGREE ON AN EASTWARD TRACK THROUGHOUT THE FORECAST PERIOD. THE JTWC
TRACK FORECAST IS PLACED WITH MEDIUM CONFIDENCE, IN LINE WITH THE
BULK OF GUIDANCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT WITH ALL
MODELS SUGGESTING WEAKENING FROM TAU 0 ONWARD. MODELS ALSO AGREE ON
DISSIPATION NEAR TAU 48-60, SUPPORTING THE JTWC INTENSITY FORECAST
WITH HIGH CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   INTENSITY 00-72 HR: HIGH//
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