WDPN33 PGTW 300900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (ROKE) WARNING NR 
009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.2N 137.9E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 377 NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 23 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM
CONTINUED TO ACCELERATE NORTHEASTWARD UNDER THE PREVAILING 
WESTERLIES. LOW LEVEL CLOUD STREAKS ALONG THE WESTERN SIDE FEEDING
INTO AN OBSCURED LOW LEVEL CIRCULATION (LLC) HAVE BECOME INCREASINGLY 
EXPOSED AS THE CENTRAL CONVECTION IS SHEARED NORTHEASTWARD. THE 
INITIAL POSITION IS DERIVED AT USING LOW CLOUD TRACING INTO THE 
OBSCURED LLC. THE INITIAL INTENSITY IS BASED ON AN OVERALL ASSESSMENT 
OF AGENCY AND AUTOMATED DVORAK ESTIMATES THAT ARE ON A 
WEAKENING TREND.

INITIAL WIND RADII BASIS: PERSISTENCE.

CURRENT STEERING MECHANISM: MID-LEVEL SUBTROPICAL RIDGE (STR) TO
THE SOUTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T4.5 - 77 KTS
   KNES: T4.0 - 65 KTS
   CIMSS SATCON: 53 KTS AT 300418Z
   CIMSS ADT: 51 KTS AT 300540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TS ROKE WILL CONTINUE EAST-NORTHEASTWARD 
THROUGHOUT THE FORECAST. AROUND TAU 36, A MID-LATITUDE SHORTWAVE
TROUGH WILL DIG IN FROM THE NORTH AND WEAKEN THE STEERING STR AND
BRING IN A SECONDARY STR BEHIND IT THAT WILL COMPETE WITH THE 
STEERING, LEADING TO A DECELERATION IN THE STORM MOTION. THE 
UNFAVORABLE CONDITIONS WILL GRADUALLY WEAKEN THE SYSTEM DOWN TO
40KTS BY TAU 72. CONCURRENTLY AROUND TAU 36, AS THE SYSTEM GETS
EMBEDDED DEEPER INTO THE PREVAILING WESTERLIES AND APPROACH THE
BAROCLINIC ZONE, TS 20W WILL BEGIN SUBTROPICAL TRANSITION AND BY
TAU 72 WILL TRANSFORM INTO A GALE-FORCE SUBTROPICAL CYCLONE.  

MODEL DISCUSSION: NUMERICAL MODELS ARE IN TIGHT AGREEMENT BUT GIVEN
THE COMPLEX STEERING BEYOND TAU 36, THERE IS ONLY MEDIUM CONFIDENCE
IN THE JTWC TRACK AND INTENSITY FORECASTS. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM//
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