WDPN33 PGTW 012100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (ROKE) WARNING NR 
015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 35.4N 150.2E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 514 NM EAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 19 KTS
   SIGNIFICANT WAVE HEIGHT: 27 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
OVERALL SYMMETRICAL CENTRAL DENSE OVERCAST (CDO) OBSCURING A
COMPACT LOW LEVEL CIRCULATION CENTER (LLCC). ADDITIONALLY, WATER
VAPOR IMAGERY SHOWS STRONG POLEWARD OUTFLOW STREAMING TOWARD THE
NORTHEAST AWAY FROM THE SYSTEMS CENTER. AN EARLIER 011641Z AMSR2
MICROWAVE IMAGE DEPICTS A DEEP CONVECTIVE BAND OVER THE NORTHERN
QUADRANT, WRAPPING INTO THE CORE OF THE SYSTEM. THE INITIAL
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON ANIMATED
SHORTWAVE INFRARED IMAGERY ALONG WITH THE AFOREMENTIONED AMSR2
MICROWAVE IMAGE AND WITHIN CLOSE PROXIMITY TO AGENCY DVORAK POSITION
FIXES. THE INITIAL INTENSITY OF 60 KNOTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON A COMBINATION OF PGTW AMD RJTD DVORAK CURRENT
INTENSITY'S, WHICH ALIGN WITH THE RECENT SATELLITE CONSENSUS
ESTIMATES. ENVIRONMENTAL CONDITIONS REMAIN GENERALLY UNFAVORABLE
WITH HIGH VWS, AND MARGINAL SSTS (25-26C) OFFSET BY VERY STRONG
POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE EAST 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   CIMSS SATCON: 62 KTS AT 011740Z
   CIMSS ADT: 82 KTS AT 011430Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 30+ KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 20W CONTINUES TO COMMENCE SUBTROPICAL
TRANSITION (STT), WITH CIMSS AUTOMATED PHASE CLASSIFICATION
INDICATING THE SYSTEM IS BORDERLINE TROPICAL AND SUBTROPICAL. THE
OVERALL TRACK REMAINS CONSISTENT WITH THE PREVIOUS FORECAST, AS THE
SYSTEM TRANSITS QUICKLY NORTHEASTWARD WITHIN ENVIRONMENTAL
CONDITIONS THAT ARE GENERALLY UNFAVORABLE WITH HIGH VWS, AND
MARGINAL SSTS (25-26C) OFFSET BY VERY STRONG POLEWARD OUTFLOW.
THESE UNFAVORABLE CONDITIONS WILL CONTINUE TO IMPACT TS 20W, WHICH
WILL RESULT IN A DECREASING INTENSITY TREND. ADDITIONALLY, OVER THE
NEXT 24 HOURS, THE TRACK MOTION WILL BEGIN TO SLOW WITH THE TRACK
SHIFTING MORE EASTWARD AS THE STEERING RIDGE WEAKENS. AFTER TAU 24,
THE TRACK MOTION SLOWS EVEN FURTHER AS THE SYSTEM BECOMES BLOCKED
BY A TRANSITORY ANTICYCLONE WHICH BUILDS POLEWARD OF THE SYSTEMS
PATH. AS THIS OCCURS THE INTENSITY WILL CONTINUE TO DECREASE
FURTHER AS SEA SURFACE TEMPERATURES COOL ALONG WITH DRY AIR
ENTRAINMENT BECOMING ADVECTED INTO THE SYSTEMS CORE. BY TAU 36, TS
20W IS EXPECTED TO COMPLETE STT AS THE SYSTEM BECOMES POSITIONED
UNDER A MID-LEVEL COLD CORE LOW.  

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE REMAINS IN GOOD
AGREEMENT WITH ONLY A 73NM CROSS TRACK SPREAD BETWEEN CONSENSUS
MEMBERS THROUGH TAU 36, WITH THE EXCEPTION OF NAVGEM WHICH REMAINS
ON THE NORTHERN SIDE OF TRACK GUIDANCE. THEREFORE, THERE IS HIGH
CONFIDENCE IN THE JTWC TRACK FORECAST. INTENSITY GUIDANCE REMAINS
MIXED AS COAMPS-TC (NAVGEM) AND HWRF REPRESENTING THE HIGH END OF
GUIDANCE, WHILE GFS AND DECAY-SHIPS SHOW A RAPID WEAKENING FROM THE
INITIAL INTENSITY. FOR THESE REASONS THE JTWC INTENSITY FORECAST IS
ASSESSED WITH MEDIUM CONFIDENCE AND FOLLOWS CLOSELY TO THE
MULTI-MODEL CONSENSUS. 

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