WDPN32 PGTW 280900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (SHANSHAN) WARNING NR 028//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 30.0N 130.0E
   INITIAL INTENSITY: 100 KTS
   GEOGRAPHIC REFERENCE: 187 NM SOUTH OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 32 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TYPHOON (TY) 11W HAS ACCELERATED POLEWARD OVER THE PAST SIX HOURS,
WITH A TROCHOIDAL (WOBBLE) TRACK MOTION EVIDENT IN ANIMATED RADAR 
IMAGERY, HOWEVER, TRACK SPEEDS REMAIN HIGHLY VARIABLE AND BELOW 
CLIMATOLOGICAL TRACK SPEEDS. ANIMATED ENHANCED INFRARED (EIR) 
SATELLITE 
IMAGERY DEPICTS A RAGGED EYE AND WEAKENING, MORE FRAGMENTED EYEWALL, 
WITH WARMING CLOUD TOP TEMPERATURES. BASED ON THE EIR IMAGERY AND 
HOURLY RADAR FIXES, THERE IS HIGH CONFIDENCE IN THE INITIAL POSITION. 
DESPITE NEAR-RADIAL OUTFLOW AND LOW VERTICAL WIND SHEAR, TY 11W IS 
BEGINNING TO INTERACT WITH THE SOUTHERN PORTION OF KYUSHU ISLAND, 
LEADING TO A SLIGHT WEAKENING TREND. SURFACE OBSERVATIONS FROM YAKU-
SHIMA, APPROXIMATELY 30 NM NORTHEAST, INDICATE MAXIMUM SUSTAINED 
SURFACE WINDS OF ABOUT 63 KNOTS (ADJUSTED TO 1-MINUTE AVERAGE). THE 
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON A BLEND OF 
THE AGENCY SUBJECTIVE DVORAK ESTIMATES AND THE CIMSS OBJECTIVE 
INTENSITY ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE BUT 64-KNOT WIND RADII WERE
ADJUSTED SLIGHTLY BASED ON SURFACE OBSERVATIONS FROM YAKU-SHIMA. 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T5.5 - 102 KTS
   KNES: T5.5 - 102 KTS
   CIMSS SATCON: 100 KTS AT 280457Z
   CIMSS ADT: 102 KTS AT 280530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 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: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TY 11W IS FORECAST TO TRACK NORTHWARD THROUGH
TAU 24 TURNING SHARPLY EASTWARD AFTER IT MAKES LANDFALL OVER
WESTERN KYUSHU. TY 11W WILL WEAKEN GRADUALLY AS IT APPROACHES
KYUSHU DUE TO INTERACTION WITH LAND AND WILL RAPIDLY WEAKEN AS IT
TRACKS INLAND THROUGH THE FORECAST PERIOD. TRACK SPEEDS WILL REMAIN 
VERY SLOW (3-4 KNOTS) ESPECIALLY AFTER TAU 36 WHEN THE MIDLATITUDE 
FLOW TO THE NORTH BECOMES MORE ZONAL LEADING TO A WEAK STEERING 
ENVIRONMENT.      

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 36 WITH A 40-NM CROSS-TRACK SPREAD AT TAU 24 AND TAU
36. HOWEVER, DETERMINISTIC GUIDANCE DIVERGES SIGNIFICANTLY WITH LOW
CONFIDENCE IN THE JTWC TRACK FORECAST AFTER TAU 36. WITH THE EXCEPTION 
OF THE GALWEM AND JGSM TRACKERS, WHICH SHOW UNREALISTICALLY FAST TRACK 
SPEEDS OVER NORTHERN HONSHU, THE BULK OF THE GUIDANCE SUPPORTS THE 
GENERAL TRACK PHILOSOPHY. HOWEVER, GUIDANCE HAS BEEN INCONSISTENT FROM 
RUN-TO-RUN. CONSEQUENTLY, THE JTWC FORECAST REMAINS CONSISTENT WITH 
THE 
PREVIOUS FORECAST. THE 280000Z ECMWF ENSEMBLE (EPS) SUPPORTS THE JTWC 
TRACK FORECAST WITH ABOUT 90 PERCENT OF THE SOLUTIONS SHOWING A SLOW, 
MEANDERING EASTWARD TRACK THROUGH TAU 72 THEN A SLOW NORTHEASTWARD 
TRACK THROUGH TAU 120. THE 280000Z GFS ENSEMBLE (GEFS) SHOWS MORE 
ERRATIC, SLOWER SOLUTIONS OVER THE WESTERN PORTION OF JAPAN.          

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