WDPN32 PGTW 200300

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//

SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W (EIGHTEEN)

WARNING NR 004//

RMKS/

1. FOR METEOROLOGISTS.

2. 6 HOUR SUMMARY AND ANALYSIS.



SUMMARY:

   INITIAL POSITION: 29.4N 127.4E

   INITIAL INTENSITY: 30 KTS

   GEOGRAPHIC REFERENCE: 251 NM SOUTH-SOUTHWEST OF SASEBO, JAPAN

   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 10 KTS

   SIGNIFICANT WAVE HEIGHT: 12 FEET



SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:

ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS PERSISTENT

DEEP CONVECTION OVER A PARTIALLY OBSCURED LOW-LEVEL CIRCULATION

CENTER (LLCC). CONVECTIVE BANDING WRAPS ALONG THE NORTHERN PERIPHERY.

WATER VAPOR IMAGERY REVEALS EQUATORWARD OUTFLOW INTO AN UPPER-LEVEL

CYCLONE TO THE SOUTHWEST AND WEAK POLEWARD OUTFLOW INTO AN

UPPER-LEVEL RIDGE TO THE NORTHEAST. THE POSITION AND INTENSITY IS

ANALYZED WITH HIGH CONFIDENCE BASED ON A 200020Z METOP-B ASCAT WIND

VECTOR IMAGE REVEALING A WELL-DEFINED LLCC WITH ENHANCED WINDS ALONG

THE EASTERN PERIPHERY OF CENTER.



INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND

RADII).



CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE TO THE EAST



AGENCY DVORAK AND AUTOMATED FIXES:

   PGTW: T2.0 - 30 KTS

   RJTD: T1.5 - 25 KTS

   KNES: T1.5 - 25 KTS

   CIMSS ADT: 33 KTS AT 192030Z



FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL

   VWS: 10-15 KTS

   SST: 29-30 CELSIUS

   OUTFLOW: MODERATE DUAL-CHANNEL



ANALYSIS CONFIDENCE:

   INITIAL POSITION: HIGH

   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: TD 18W WILL CONTINUE TO TRACK NORTHEASTWARD

UNDER THE STEERING INFLUENCE OF THE SUBTROPICAL RIDGE TO THE

NORTHEAST. BETWEEN TAU 48-72, THE CIRCULATION WILL HAVE CURVED

EASTWARD WHILE MAKING LANDFALL ON KYUSHU. VERTICAL WIND SHEAR WILL

GRADUALLY INCREASE UNFAVORABLY AS THE SYSTEM APPROACHES THE

UPPER-LEVEL JET TO THE NORTH. DRY AIR WILL CONTINUE TO IMPOSE UPON

THE CIRCULATION FROM THE SOUTH THROUGHOUT THE FORECAST PERIOD.

SLIGHT INTENSIFICATION TO A PEAK OF 35KTS WILL OCCUR IN THE

EARLY-TERM FORECAST WHILE SHEAR IS MARGINAL. HOWEVER, THE

UPPER-LEVEL FLOW WILL BECOME STREAMLINED AND SHEAR WILL INCREASE

UNFAVORABLY, RESULTING IN WEAKENING AFTER TAU 36. BY THE END OF THE

FORECAST PERIOD, TD 18W WILL DISSIPATE OVER LAND ON KYUSHU.



MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE HAS COME INTO BETTER

AGREEMENT THAT TD 18W WILL CURVE TOWARDS KYUSHU AFTER TAU 48,

HOWEVER THE STRENGTH OF THE RIDGE VARIES FROM MODEL TO MODEL. THE

GEFS ENSEMBLE DEPICTS THE SHARPEST CURVE TO THE EAST, WHILE UKMET

LIES FARTHEST TO THE WEST. THE INTENSITY GUIDANCE IS ALSO IN BETTER

AGREEMENT, WITH PEAK INTENSITIES CLOSER TO 35KTS BETWEEN TAU 24-48.



FORECAST CONFIDENCE:

   TRACK 0 - 72 HR: MEDIUM

   INTENSITY 0 - 72 HR: HIGH//

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