WDPN31 PGTW 242100
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: 28.1N 135.2E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 489 NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A SMALL
SYSTEM TRAILING A COLD FRONT SOUTHEAST OF JAPAN THAT IS STRUGGLING
TO CONSOLIDATE UNDER STRONG VERTICAL WIND SHEAR (VWS) AS EVIDENCED
BY ITS COLD DENSE OVERCAST OFFSET EASTWARD AND MOSTLY EXPOSING THE
LOW LEVEL CIRCULATION (LLC) ONCE AGAIN. THE INITIAL INTENSITY IS
PLACED WITH HIGH CONFIDENCE BASED ON THE LLC FEATURE IN THE EIR
LOOP. THE INITIAL INTENSITY OF 30KTS IS ALSO PLACED WITH HIGH
CONFIDENCE BASED ON THE AVERAGE OF CLOSELY-VALUED AGENCY AND
AUTOMATED DVORAK ESTIMATES AND REFLECTS THE MOSTLY SUSTAINED 6-HR
CONVECTIVE SIGNATURE. ANALYSIS INDICATES A MARGINAL ENVIRONMENT
WITH WARM SSTS, WEAK RADIAL OUTFLOW, AND MODERATE TO STRONG VWS.

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

CURRENT STEERING MECHANISM: COMPETING STEERING FLOW IN A COL
BETWEEN SUBTROPICAL RIDGES (STR) TO THE WEST AND EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.0 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 31 KTS AT 241730Z
   CIMSS DPRNT: 30 KTS AT 241800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: EXTENDED THE FORECAST TO TAU 96 TO
INDICATE EXTRA-TROPICAL TRANSITION. 

FORECAST DISCUSSION: THE STR TO THE EAST WILL BECOME THE
PREDOMINANT STEERING MECHANISM AND DRIVE THE SYSTEM NORTHWESTWARD.
BY TAU 36, IT WILL CREST THE STR AXIS THEN RECURVE AND ACCELERATE
NORTHEASTWARD ON THE POLEWARD SIDE OF THE STR. THE MARGINAL
ENVIRONMENT WILL BECOME UNFAVORABLE AFTER TAU 12 AS THE CYCLONE
DRIFTS INTO STRONGER VWS, ERODING THE SYSTEM DOWN TO 25KTS. BY TAU
72, TD 18W IS EXPECTED TO SLIGHTLY RE-INTENSIFY TO 30KTS AS THE VWS
RELAXES. CONCURRENTLY, IT WILL ALSO BEGIN EXTRA-TROPICAL TRANSITION
AS IT APPROACHES THE BAROCLINIC ZONE, AND BY TAU 96, WILL TRANSFORM
INTO A COLD CORE LOW. THERE IS A DISTINCT POSSIBILITY THAT TD 18W
WILL DISSIPATE AFTER TAU 24 MOSTLY DUE TO THE INCREASED VWS. 

MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL AGREEMENT WITH
THE TRACK FORECAST WITH NOTABLE OUTLIERS LIKE GFS, NVGM, AND ECMF
THAT RANDOMLY DEFLECT OR REVERSE THE TRAJECTORY AWAY FROM THE MAIN
PACK AFTER TAU 36, AN INDICATION OF A WEAK VORTEX. IN VIEW OF THIS,
THE INITIAL STORM MOTION UNCERTAINTY COMING OUT OF A COL, AND THE
POSSIBILITY OF AN EARLY DISSIPATION LEND LOW CONFIDENCE TO THE JTWC
TRACK AND INTENSITY FORECASTS.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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