WDPN32 PGTW 270900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (SHANSHAN) WARNING NR 024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.5N 130.4E
   INITIAL INTENSITY: 105 KTS
   GEOGRAPHIC REFERENCE: 183 NM NORTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
AS INDICATED ON ANIMATED RADAR IMAGERY AND VISIBLE SATELLITE IMAGERY, 
TYPHOON (TY) 11W IS COMPLETING AN EYEWALL REPLACEMENT CYCLE, WITH 
RAPID DETERIORATION OF THE INNER EYEWALL WITHIN A CLEARLY DEFINED 
OUTER EYEWALL. OVER THE PAST SIX HOURS, THE SYSTEM WEAKENED SLIGHTLY 
WITH A CLOUD-FILLED, RAGGED EYE EVIDENT. HOWEVER, RECENT (270500-
0800Z) ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS AN IMPROVED, 
CLEARING 12NM EYE, WHICH SUPPORTS THE INITIAL POSITION WITH HIGH 
CONFIDENCE. THE SYSTEM IS LOCATED ABOUT 22 NM EAST-NORTHEAST OF KIKAI-
JIMA, WHICH IS REPORTING 10-MINUTE SUSTAINED NORTHWESTERLY WINDS OF 
40-45 KNOTS OVER THE PAST FEW HOURS. DESPITE PERSISTENT NORTH-
NORTHEASTERLY VERTICAL WIND SHEAR, THE SYSTEM HAS REMAINED RESILIENT 
MAINTAINING RADIAL OUTFLOW, WITH ROBUST EQUATORWARD OUTFLOW EVIDENT IN 
THE ANIMATED WATER VAPOR RGB IMAGERY. THE INITIAL INTENSITY IS 
ASSESSED AT 105 KNOTS BASED ON AGENCY DVORAK CURRENT INTENSITY 
ESTIMATES OF 102 KNOTS COUPLED WITH CIMSS OBJECTIVE INTENSITY 
ESTIMATES RANGING FROM 103 TO 114 KNOTS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T5.5 - 102 KTS
   RCTP: T5.5 - 102 KTS
   KNES: T5.5 - 102 KTS
   CIMSS SATCON: 114 KTS AT 270700Z
   CIMSS ADT: 107 KTS AT 270600Z
   CIMSS AIDT: 107 KTS AT 270600Z
   CIMSS DPRINT: 111 KTS AT 270600Z
   CIMSS DMINT: 103 KTS AT 270424Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 20-25 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: EYEWALL REPLACEMENT CYCLE

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

3. FORECAST REASONING.

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

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. 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 (6-8 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: THE BULK OF THE DETERMINISTIC GUIDANCE SUPPORTS THE 
JTWC TRACK FORECAST WITH THE GLARING EXCEPTION OF GFS AND THE UKMO 
ENSEMBLE MEAN (UEMI). GFS CONTINUES TO STALL THE SYSTEM NEAR KYUSHU 
ISLAND AS THE STR BUILDS TO THE WEST AND EAST OF THE SYSTEM, TRAPPING 
IT WITHIN A COMPETING STEERING ENVIRONMENT. ECMWF QUICKLY TRACKS THE 
SYSTEM EASTWARD, ACROSS CENTRAL HONSHU. WITH A FEW MINOR EXCEPTIONS, 
THE 261800Z ECMWF ENSEMBLE (EPS) SUPPORTS THE EASTWARD TRACK. IN STARK 
CONTRAST, THE 270000Z GFS ENSEMBLE (GEFS) IS SPLIT, WITH ABOUT 40 
PERCENT OF THE SOLUTIONS TRACKING THE SYSTEM EASTWARD WHILE 60 PERCENT 
OF THE SOLUTIONS SHOW A SLOW, ERRATIC TRACK NEAR KYUSHU OR FURTHER 
INLAND NEAR SHIKOKU AND WESTERN JAPAN. DUE TO THIS INCREASING 
UNCERTAINTY IN THE EXTENDED FORECAST PERIOD (TAU 72 TO TAU 120), THERE 
IS LOW CONFIDENCE IN THE JTWC TRACK 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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