WDPN32 PGTW 261500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (SHANSHAN) WARNING NR 021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.8N 131.9E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 232 NM EAST-NORTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 33 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
PERSISTENT DEEP CONVECTIVE BANDING SURROUNDING A DEVELOPING COMPACT
EYE THAT IS INTERMITTENTLY OBSCURED BY CIRRUS ALOFT BUT HAS BEEN
CONTINUOUSLY EVIDENT IN RECENT MICROWAVE SATELLITE IMAGERY. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A RECENT
PGTW GEOSTATIONARY SATELLITE FIX, RECENT RADAR FIXES FROM THE JAPAN
METEOROLOGICAL AGENCY, AND 260838Z SSMIS 37 GHZ IMAGERY. THE
INITIAL INTENSITY OF 90 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED
ON BASED ON A CONSENSUS OF MULTI-AGENCY SUBJECTIVE DVORAK AND
AUTOMATED INTENSITY ESTIMATES, INCLUDING T5.0 DVORAK VALUES (90 KTS) 
FROM PGTW AND RCTP AND A 261130Z UW-CIMSS ADT ESTIMATE OF 87 KTS. 
ALTHOUGH STRUCTURAL IMPROVEMENTS INDICATE THAT THE INTENSIFICATION 
TREND CONTINUES, UPPER-LEVEL FEATURE TRACK WINDS AND ANIMATED WATER 
VAPOR IMAGERY REVEAL PERSISTENT NORTHEASTERLY VERTICAL WIND SHEAR 
AWAITING THE SYSTEM JUST DOWNSTREAM.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T5.0 - 90 KTS
   KNES: T4.5 - 77 KTS
   CIMSS ADT: 87 KTS AT 261130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE PROJECTED TRACK HAS SHIFTED
SLIGHTLY TO THE WEST OF THE PREVIOUS FORECAST. OTHERWISE, THERE ARE
NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TYPHOON 11W IS EXPECTED TURN POLEWARD OVER THE
NEXT 48 HOURS, THEN ROUND THE AXIS OF THE STEERING RIDGE AND TURN
EASTWARD TOWARD KYUSHU THEREAFTER. THE CURRENT FORECAST PLACES THE
LANDFALL POINT SOUTH OF SASEBO JUST AFTER TAU 72. DURING THE
EXTENDED FORECAST PERIOD, THE SYSTEM WILL MOVE INLAND AND SLOWLY
ACCELERATE POLEWARD AND EASTWARD AHEAD OF A DEVELOPING MID-LATITUDE
TROUGH. EXTRATROPICAL TRANSITION IS EXPECTED TO BEGIN BY TAU 120 AS
THE SYSTEM INTERACTS WITH THE MID-LATITUDE TROUGH, ALTHOUGH IT
REMAINS TOO EARLY TO TELL WHETHER THE TRANSITION PROCESS WILL
CONTINUE OR THE SYSTEM WILL DISSIPATE OVER LAND BEYOND TAU 120, AS
A FAIR PROPORTION OF THE AVAILABLE DETERMINISTIC AND ENSEMBLE MODEL
GUIDANCE INDICATES. THE CURRENT INTENSIFICATION TREND IS EXPECTED
TO CONTINUE FOR THE NEXT 24 HOURS, SUPPORTED BY PASSAGE OVER VERY
WARM WATER AND FAVORABLE EQUATORWARD OUTFLOW. HOWEVER,
INTENSIFICATION WILL BE LIMITED AS VERTICAL WIND SHEAR INCREASES
DUE TO PERSISTENT NORTHEASTERLY FLOW ALOFT AND AS UPPER-LEVEL
OUTFLOW DECREASES, PARTIALLY DUE TO FILLING OF A TROPICAL UPPER 
TROPOSPHERIC TROUGH CELL TO THE SOUTH THAT IS CURRENTLY SUPPORTING 
THE SYSTEM. PASSAGE OVER LAND WILL LEAD TO STEADY WEAKENING AFTER TAU 
72.

MODEL DISCUSSION: THE LATEST MODEL GUIDANCE PACKAGE HAS AGAIN
EXTENDED THE AXIS OF THE SUBTROPICAL STEERING RIDGE FARTHER TO THE
WEST, NECESSITATING A COMMENSURATE ADJUSTMENT TO THE FORECAST
TRACK. HOWEVER, THE SHIFT IN THE GUIDANCE IS LESS PRONOUNCED THAN
OBSERVED IN PREVIOUS RUNS. FOR THE PAST FOUR CYCLES, BOTH
DETERMINISTIC AND ENSEMBLE MODEL SOLUTIONS HAVE BEEN CONSISTENT IN 
THEIR GENERAL DEPICTION OF THE STEERING PATTERN. PATTERNS IN THE 
TRACK FORECAST GUIDANCE ARE SIMILAR TO THE PREVIOUS CYCLE. NAVGEM AND 
UKMET-BASED MODELS SUGGEST A WIDER TURN FARTHER THE WEST EARLY ON, 
BUT MOST CONSENSUS MODEL INDICATE LANDFALL TO THE SOUTH OF SASEBO 
BETWEEN TAU 72 AND TAU 96 AT THE LATEST. AND ONCE AGAIN ON THE LATEST 
RUN, THE UKMET AND GFS DETERMINISTIC SOLUTIONS DEPICT DISSIPATION 
AFTER LANDFALL RATHER THAN EXTRATROPICAL TRANSITION. BUT THE MAJORITY 
OF THE GUIDANCE, BOTH DETERMINISTIC MODELS AND ENSEMBLE MEMBERS, 
SUPPORT THE CURRENT FORECAST SCENARIO OF A STEADY TURN AROUND THE 
RIDGE AXIS FOLLOWED BY SLOW BUT STEADY ACCELERATION OVER LAND AND THE 
BEGINNING OF EXTRATROPICAL TRANSITION LATE IN THE FORECAST PERIOD. 
NOT MUCH HAS CHANGED WITH THE ASSESSMENT OF UNCERTAINTY SINCE THE 
PREVIOUS CYCLE, SO BOTH TRACK AND INTENSITY FORECAST CONFIDENCE 
REMAIN MEDIUM THROUGH THE FORECAST PERIOD.

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