WDPN33 PGTW 281500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (ROKE) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.1N 131.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 294 NM SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) ROKE HAS QUICKLY AND STEADILY CONSOLIDATED OVER
THE PAST SIX HOURS AND HAS DEVELOPED A CENTRAL DENSE OVERCAST (CDO)
WITH EMBEDDED CONVECTIVE TOWER CLOUD TOP TEMPS AT TIMES REACHING AS
LOW AS NEGATIVE 88C. HOWEVER AT PRESENT THE CONVECTION DOES NOT
APPEAR TO BE WRAPPING INTO A DEFINED CENTER SO THE LOW LEVEL CENTER
LIKELY HAS YET TO FULLY CONSOLIDATE. A 281130Z NOAA-19 AMSU-B 89GHZ
MICROWAVE IMAGE PROVIDED WEAK SUPPORT TO THE INITIAL POSITION BUT
DID CONFIRM THAT NASCENT BANDING FEATURES ARE BEGINNING TO WRAP
INTO THE CENTER FROM THE NORTHWEST. BUT DUE TO A LACK OF RECENT
HIGH RESOLUTION MICROWAVE OR SCATTEROMETER DATA, THE INITIAL
POSITION IS ASSESSED WITH LOW CONFIDENCE. THE INITIAL INTENSITY IS
ASSESSED AT 35 KNOTS WITH MEDIUM CONFIDENCE, HEDGED ABOVE THE
MULTI-AGENCY T2.0 ESTIMATES IN LIGHT OF THE DRAMATICALLY IMPROVED
STRUCTURE AND THE ADT, AIDT AND OPEN-AIIR ESTIMATES OF 34 KNOTS, 35
KNOTS AND 38 KNOTS RESPECTIVELY. ANALYSIS REVEALS A FAVORABLE
ENVIRONMENT WITH LOW VWS, MODERATE RADIAL OUTFLOW AND WARM SSTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 34 KTS AT 281150Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS ROKE HAS SLOWED DOWN A BIT SINCE THE
PREVIOUS WARNING, NOW MOVING NORTH-NORTHWEST AT ABOUT 8 KNOTS,
SLOWING AS IT APPROACHES THE AXIS OF THE STR TO THE EAST. OVER THE
NEXT 12 HOURS THE SYSTEM SHOULD START TO TURN MORE NORTHWARD, ROUND
THE AXIS NEAR TAU 12 AND THEN SCOOT OFF TO THE NORTHEAST ALONG THE
RIDGE. THE STEERING RIDGE IS EXPECTED TO WEAKEN AND FLATTEN AFTER
TAU 36, ALLOWING THE SYSTEM TO TURN A BIT MORE TO THE EAST THROUGH
TAU 72. WITH ENVIRONMENTAL CONDITIONS FORECAST TO REMAIN FAVORABLE
FOR THE NEXT 24 TO 36 HOURS, ONCE THE CORE OF TS ROKE BECOMES MORE
VERTICALLY STACKED, IT WILL INTENSIFY RATHER QUICKLY, UP TO A PEAK
OF AT LEAST 50 KNOTS BY TAU 24. BY TAU 48 HOWEVER, SHEAR IS
EXPECTED TO SHARPLY INCREASE AND THE UPPER-LEVEL ANTICYCLONE
CURRENTLY OVER THE SYSTEM WILL SLIDE TO THE SOUTHWEST AND BEGIN TO
IMPART CONVERGENT WESTERLY FLOW OVER THE SYSTEM, COMMENCING A
WEAKENING TREND. AROUND TAU 36 A 500MB MINOR SHORTWAVE TROUGH WILL
SLIDE DOWN ACROSS JAPAN AND KICK OF CYCLOGENESIS JUST EAST OF TOKYO
ALONG THE SOUTHERN END OF A COLD FRONT DRAPED ACROSS THE REGION
FROM WHAT WAS TY 19W FAR TO THE NORTH. THIS NEW BARCLINIC LOW WILL
SLIDE DUE EAST THROUGH TAU 72, DRAGGING A WEAK COLD FRONT IN ITS
WAKE ROUGHLY ALONG THE 31ST LATITUDE LINE, WITH A TRANSITORY HIGH
PRESSURE SYSTEM MOVING EAST OFF THE COAST OF NORTHERN JAPAN. BY TAU
72, WEAKENED BY PERSISTENT STRONG VWS AND CONVERGENT FLOW ALOFT, A
MUCH SHALLOWER TS ROKE WILL BE APPROACHING THIS LINE BUT WILL BE
BLOCKED FROM MUCH IN THE WAY OF FURTHER NORTHEAST MOVEMENT BY THE
STRONG NORTHEASTERLY FLOW POURING SOUTHWARD FROM THE HIGH. AS THE
HIGH MOVES FURTHER EAST, WINDS SHIFT TO EASTERLY AND WILL PUSH THE
WEAK TS ROKE TO THE WEST. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS FAIRLY GOOD
AGREEMENT THROUGH TAU 36 BUT STARTS TO DIVERGE AFTER THIS POINT.
NAVGEM HAS JOINED THE PACK NOW, LEAVING JGSM AS THE SOLE OUTLIER TO
THE WEST, WITH THE REMAINDER OF THE CONSENSUS MEMBERS CONSTRAINED
WITHIN A 70NM ENVELOPE AT TAU 48. AT THIS POINT THE TRAIN GOES OFF
THE RAILS. BY TAU 72, THE JGSM HAS ALREADY TURNED THE TRACK TO THE
NORTH TO A POINT SOUTH OF SHIKOKU, WHILE THE EGRR RUNS STRAIGHT TO
THE NORTHEAST, COMPLETELY IGNORING THE STRONG ANTICYCLONE THERE,
WHILE THE GFS AND GALWEM START TO SLOW DOWN AND LAG THE CONSENSUS
MEAN. BY TAU 96 THE MAJORITY OF THE GUIDANCE, WITH THE NOTABLE
EXCEPTION OF NAVGEM AND THE ECMWF WHICH CARRY THE SYSTEM TO THE
NORTHEAST INTO THE RIDGE, BEGINS TO SHOW A SHARP TURN TO THE
NORTHWEST OR WEST IN THE CASE OF THE GFS. BY TAU 120, GFS HAS TAKEN
THE SYSTEM WEST ALL THE WAY TO 133E WHILE THE EGRR HAS TRACKED FAR
OUT THE EAST, LEADING TO A SPREAD OF 600NM. THE REMAINDER OF THE
GUIDANCE SHOW A TURN TO THE NORTHWEST, SPREAD ACROSS THIS LARGE
ENVELOPE. THE JTWC FORECAST REMAINS CONSISTENT WITH THE PREVIOUS
FORECAST AND LIES GENERALLY CLOSE TO THE MULTI-MODEL CONSENSUS MEAN
WITH LOW CONFIDENCE AFTER TAU 72. INTENSITY GUIDANCE IS MARGINALLY
BETTER, WITH THE GFS AND COAMPS-TC (NAVGEM) SHOWING NO
INTENSIFICATION THROUGH TAU 48 AND VERY SLOW WEAKENING THEREAFTER.
MEANWHILE THE GFS VERSION OF COAMPS-TC IS VERY AGGRESSIVE, PEAKING
THE SYSTEM AT 60 KNOTS AT TAU 24 AND THE REMAINDER OF THE GUIDANCE
IS CLOSELY PACKED ABOUT THE CONSENSUS MEAN. THE JTWC FORECAST IS
ABOUT 5 KNOTS HIGHER THAN THE PEAK OF THE MEAN THROUGH TAU 36 THEN
CLOSELY TRACKS THE MEAN THROUGH THE WEAKENING PHASE. CONFIDENCE IS
MEDIUM INITIALLY, BUT DROPS TO LOW IN THE LATER FORECAST PERIOD.

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