WDPN32 PGTW 191500

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

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

WARNING NR 002//

RMKS/

1. FOR METEOROLOGISTS.

2. 6 HOUR SUMMARY AND ANALYSIS.



SUMMARY:

   INITIAL POSITION: 27.9N 127.1E

   INITIAL INTENSITY: 30 KTS

   GEOGRAPHIC REFERENCE: 344 NM SOUTH-SOUTHWEST OF SASEBO

   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 09 KTS

   SIGNIFICANT WAVE HEIGHT: 16 FEET



SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:

ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A

PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC), WITH A REGION

OF SYMMETRIC, INTENSE CONVECTION PERSISTING OVER THE NORTHWEST

QUADRANT. ANIMATED RADAR IMAGERY SHOWS MULTIPLE CONVECTIVE BANDS OVER

THE EASTERN SEMICIRCLE WRAPPING INTO THE NORTHWEST QUADRANT. AN

181156Z ASCAT-B IMAGE DEPICTS A SYMMETRIC, WELL-DEFINED CIRCULATION,

WITH 25-30 KNOT WINDS OVER THE EASTERN SEMI-CIRCLE, WHICH SUPPORTS

THE INITIAL INTENSITY OF 30 KNOTS AND INITIAL POSITION WITH HIGH

CONFIDENCE. 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.



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: T2.0 - 30 KTS

   RJTD: T1.5 - 25 KTS

   KNES: T1.0 - 25 KTS

   CIMSS ADT: 31 KTS AT 191130Z

   CIMSS AIDT: 36 KTS AT 191130Z

   CIMSS D-PRINT: 28 KTS AT 191230Z



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: THERE ARE NO SIGNIFICANT CHANGES TO

THE FORECAST FROM THE PREVIOUS WARNING.



FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 18W WILL TRACK

NORTHWARD TO NORTH-NORTHEASTWARD THROUGH TAU 36 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 36, 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 30NM CROSS-TRACK SPREAD AT TAU 24. AFTER TAU

24, GUIDANCE DIVERGES WITH INCREASING UNCERTAINTY IN THE FORECAST

TRACK AFTER TAU 48. THE DETERMINISTIC 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 KNOTS NEAR TAU 48, WITH STEADY WEAKENING THROUGH TAU 72.



FORECAST CONFIDENCE:

   TRACK 00-72 HR: MEDIUM

   INTENSITY 00-72 HR: MEDIUM//

NNNN