WDPN32 PGTW 271500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (SHANSHAN) WARNING NR 025//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.6N 130.3E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 272 NM SOUTH OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 01 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TYPHOON (TY) 11W HAS COMPLETED AN EYEWALL REPLACEMENT CYCLE AND HAS 
SUBSEQUENTLY REINTENSIFIED SLIGHTLY, WITH A 25-30 NM SYMMETRIC EYE 
EVIDENT IN ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY AND 
RADAR IMAGERY, WHICH SUPPORTS THE INITIAL POSITION WITH HIGH 
CONFIDENCE. ANIMATED RADAR IMAGERY ALSO INDICATES A SIGNIFICANT STALL 
OR SLOW NORTHWESTWARD DRIFT NEAR KIKAI-JIMA, WHICH REPORTED MAXIMUM
SUSTAINED NORTHWESTERLY WINDS (10-MINUTE AVERAGE) OF 63.5 KNOTS AT
271010Z. THE SYSTEM HAS REMAINED RESILIENT MAINTAINING RADIAL OUTFLOW, 
WITH ROBUST EQUATORWARD OUTFLOW EVIDENT IN THE ANIMATED WATER VAPOR 
RGB IMAGERY, HOWEVER, SOME FLATTENING OF THE CORE CONVECTION DUE TO 
NORTHERLY VERTICAL WIND SHEAR IS EVIDENT. THE INITIAL INTENSITY IS 
ASSESSED AT 110 KNOTS BASED ON AGENCY DVORAK CURRENT INTENSITY 
ESTIMATES OF 102 TO 115 KNOTS BLENDED WITH CIMSS OBJECTIVE INTENSITY 
ESTIMATES RANGING FROM 106 TO 112 KNOTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTHEAST AND EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T5.5 - 102 KTS
   KNES: T6.0 - 115 KTS
   CIMSS ADT: 109 KTS AT 271200Z
   CIMSS AIDT: 106 KTS AT 271200Z
   CIMSS DPRINT: 107 KTS AT 271200Z
   CIMSS SATCON: 112 KTS AT 271130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: TRACK SPEEDS IN THE EXTENDED PERIOD
(TAU 72-120) HAVE BEEN DECREASED MARKEDLY AS MODEL GUIDANCE GRADUALLY 
SHIFTS AWAY FROM A RECURVE SCENARIO.  

FORECAST DISCUSSION: TY 11W IS TRACKING SLOWLY ALONG THE WESTERN
PERIPHERY OF THE STR, TOWARD A LARGE BREAK IN THE STR ASSOCIATED
WITH A MAJOR SHORTWAVE TROUGH DIGGING INTO THE SEA OF JAPAN. THIS
TROUGH IS EXPECTED TO RAPIDLY FILL AND PROPAGATE EASTWARD WITHIN
THE NEXT DAY, WITH ZONAL MIDLATITUDE FLOW FORECAST ACROSS NORTH
KOREA AND NORTHERN JAPAN THROUGH TAU 120. THIS WILL LEAD TO
UNUSUALLY SLOW TRACK SPEEDS AS THE SYSTEM TRACKS NORTHWARD TOWARD
WESTERN KYUSHU THROUGH TAU 48. DUE TO THE SLOW TRACK SPEEDS, UPWELLING 
OF COOLER WATER IS POSSIBLE AS INDICATED IN THE LATEST HAFS-A RUN, 
WHICH COULD CONTRIBUTE TO ADDITIONAL WEAKENING. TY 11W IS EXPECTED TO 
MAINTAIN ITS INTENSITY THROUGH TAU 12, WITH GRADUAL WEAKENING AS THE 
SYSTEM APPROACHES KYUSHU DUE TO INCREASED FRICTION AND NORTHERLY 
VERTICAL WIND SHEAR. AFTER TAU 48, TY 11W SHOULD TURN EASTWARD TO
EAST-NORTHEASTWARD ALONG THE NORTHWESTERN PERIPHERY OF THE STR
WITH RAPID WEAKENING AND CLIMATOLOGICALLY SLOW (6 KNOTS) TRACK SPEEDS
THROUGH TAU 120 DUE TO THE AFOREMENTIONED ZONAL MIDLATITUDE FLOW
DISPLACED TO THE NORTH. ADDITIONALLY, THE BAROCLINIC ZONE IS DISPLACED 
TOO FAR POLEWARD AND THERE IS A LACK OF A DEEP, DYNAMIC MIDLATITUDE 
MAJOR TROUGH TO PRODUCE A TYPICAL FAST RECURVE TRACK. RAPID WEAKENING 
IS EXPECTED AFTER THE SYSTEM MAKES LANDFALL AND TRACKS INLAND ACROSS 
THE MOUNTAINOUS TERRAIN OF KYUSHU, SHIKOKU AND HONSHU.         

MODEL DISCUSSION: WITH THE EXCEPTION OF THE UNREALISTICALLY FAST 
RECURVE TRACKS OF JGSM, NAVGEM AND GALWEM, THE BULK OF THE 
DETERMINISTIC GUIDANCE SUPPORTS THE JTWC TRACK FORECAST. ADDITIONAL 
MODEL TRACKERS NOW INDICATE A MUCH SLOWER TRACK AND POSSIBLE STALL 
FROM KYUSHU (GFS) TO SHIKOKU (AEMN AND UEMN) TO THE KYOTO REGION 
(ECMWF AND UKMET). ABOUT 90 PERCENT OF THE 270600Z ECMWF ENSEMBLE 
(EPS) SOLUTIONS INDICATE A SLOW TRACK FROM WESTERN TO CENTRAL HONSHU. 
THE 270600Z GFS ENSEMBLE (GEFS) INDICATES A SIMILAR SPREAD ALTHOUGH 
SHIFTED FURTHER SOUTH OVER AND TO THE SOUTH OF KYUSHU, SHIKOKU AND 
WESTERN HONSHU. DUE TO THIS INCREASING UNCERTAINTY IN THE EXTENDED 
FORECAST PERIOD (TAU 72 TO TAU 120), THERE IS LOW CONFIDENCE IN THE 
JTWC TRACK AND INTENSITY FORECAST.     

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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