WDPN33 PGTW 301500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (ROKE) WARNING NR 
010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 30.2N 140.4E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 308 NM SOUTH OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 24 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THE SYSTEM 
CONTINUED TO ACCELERATE NORTHEASTWARD DEEPER INTO THE PREVAILING 
WESTERLIES. LOW LEVEL COLD-AIR STRATOCUMULUS STREAKS ALONG THE 
WESTERN SIDE FEEDING INTO AN OBSCURED LOW LEVEL CIRCULATION (LLC)
HAVE BECOME INCREASINGLY EXPOSED AS THE CENTRAL CONVECTION IS 
SEVERELY SHEARED NORTHEASTWARD. THE INITIAL POSITION IS EXTRAPOLATED 
FROM A MICROWAVE EYE FEATURE IN THE 300847Z SSMIS 91GHZ IMAGE. THE 
INITIAL INTENSITY IS BASED ON AN OVERALL ASSESSMENT OF AGENCY AND 
AUTOMATED DVORAK ESTIMATES THAT ARE ON A WEAKENING TREND AND REFLECTS 
THE 6-HR DETERIORATION.

INITIAL WIND RADII BASIS: PERSISTENCE.

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T4.0 - 65 KTS
   KNES: T3.5 - 55 KTS
   CIMSS ADT: 51 KTS AT 300840Z

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 UNDER THE STEERING INFLUENCE OF THE STR.
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 SLIGHT
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 WITH AN EXPANDING WIND FIELD. THERE IS A DISTINCT 
POSSIBILITY THAT TS 20W WILL DISSIPATE BEFORE TAU 72 GREATLY DUE TO 
THE HIGH VWS. 

MODEL DISCUSSION: NUMERICAL MODELS ARE IN TIGHT AGREEMENT WITH A
GRADUAL AND EVEN SPREAD TO 150NM BY TAU 72, BUT GIVEN THE COMPLEX
STEERING BEYOND TAU 36 AND THE POSSIBILITY OF AN EARLY DISSIPATION,
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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