WDPN33 PGTW 290300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (ROKE)        
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.0N 131.8E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 234 NM EAST-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A COMPACT, 
RAPIDLY CONSOLIDATING SYSTEM WITH A RAGGED, 12NM EYE. A 290102Z MHS 
89GHZ MICROWAVE IMAGE REVEALS A MICROWAVE EYE FEATURE WITH SPIRAL 
BANDING OVER THE EASTERN AND NORTHERN SEMICIRCLES. ANIMATED WATER 
VAPOR IMAGERY DEPICTS ROBUST POLEWARD OUTFLOW WITH TRANSVERSE BANDING 
ALONG THE WESTERN AND NORTHERN SEMICIRCLES. ADDITIONALLY, LOW 
VERTICAL WIND SHEAR AND WARM SST VALUES (28-29C) SUPPORT FURTHER 
INTENSIFICATION. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE 
BASED ON THE EYE IN MSI AND RJTD RADAR FIXES. THE INITIAL INTENSITY 
OF 55 KTS IS BASED ON THE PGTW AND KNES DVORAK INTENSITY ESTIMATES, 
AS WELL AS THE CIMSS ADT ESTIMATE. AN UNOFFICIAL PGTW DVORAK ESTIMATE 
AT 290200Z INDICATES A DATA-T OF T4.0 (65 KNOTS). 

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T3.5 - 55 KTS
   CIMSS ADT: 55 KTS AT 282340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 20W IS A COMPACT SYSTEM AND IS FORECAST TO 
CONTINUE TO RAPIDLY CONSOLIDATE OVER THE NEXT 12 HOURS TO A PEAK 
INTENSITY OF 75 KNOTS. DUE TO THE ROBUST POLEWARD OUTFLOW AND COMPACT 
STRUCTURE OF THE SYSTEM, THERE IS SOME POTENTIAL FOR THE SYSTEM TO 
REACH A HIGHER PEAK INTENSITY IF THE EYE CAN MAINTAIN AND STRENGTHEN 
OVER THE NEXT 24 HOURS AS THE SYSTEM ROUNDS THE STR AXIS. AFTER TAU 
24, TS 20W SHOULD ENCOUNTER MIDLATITUDE WESTERLIES AS IT TRACKS ALONG 
THE NORTHWESTERN PERIPHERY OF THE STR WITH CONVERGENCE ALOFT LEADING 
TO A STEADY WEAKENING TREND THROUGH THE REMAINDER OF THE FORECAST 
PERIOD. AFTER TAU 72, THE SYSTEM IS EXPECTED TO SLOW AND STALL AS A 
LOW-LEVEL HIGH BUILDS TO THE NORTH AND NORTHEAST EFFECTIVELY BLOCKING 
ANY FURTHER POLEWARD PROGRESSION. TS 20W WILL WEAKEN SIGNIFICANTLY 
DUE TO THE UPPER-LEVEL CONVERGENCE AND BAROCLINIC INTERACTION DURING 
THE EXTENDED PERIOD.   

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
THROUGH TAU 48 WITH AN 110NM SPREAD IN SOLUTIONS. HOWEVER, THE
GUIDANCE DIVERGES QUICKLY WITH THE BULK OF THE GUIDANCE INDICATING
A QUASI-STATIONARY OR SLOW TRACK THROUGH TAU 120. THE 28/18Z NAVGEM 
RUN IS MORE COHESIVE THAN THE PREVIOUS RUN AND SHOWS A FAST 
NORTHEASTWARD TRACK, HOWEVER, THE MODEL IS DRIVING THE SYSTEM INTO 
THE LOW-LEVEL HIGH, WHICH IS UNREALISTIC. THE 281800Z ECMWF ENSEMBLE 
(EPS) AND GFS ENSEMBLE (GEFS) BOTH SHOW THE LARGE MAJORITY OF 
SOLUTIONS STALLING THE SYSTEM SOUTH OF HONSHU; VERY FEW SOLUTIONS 
INDICATE A RECURVE SCENARIO. THE TRACK CONFIDENCE AFTER TAU 72 IS DUE 
PRIMARILY TO UNCERTAINTY IN THE EXACT TRACK ONCE THE SYSTEM SLOWS AND 
STALLS. THE 281800Z COAMPS-TC ENSEMBLE INDICATES A 20 TO 30 PERCENT 
PEAK PROBABILITY OF RI THROUGH TAU 36 SUPPORTING THE JTWC INTENSITY 
FORECAST. 

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