WDPN32 PGTW 311500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 06W (KHANUN) WARNING NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.4N 131.1E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 258 NM SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 48 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
AFTER A PERIOD OF RAPID INTENSIFICATION, TYPHOON (TY) 06W HAS 
MAINTAINED INTENSITY AT 115 KNOTS. ANIMATED ENHANCED INFRARED 
SATELLITE IMAGERY (EIR) DEPICTS A SYMMETRIC EYEWALL SURROUNDING A
27NM ROUND EYE (EYE TEMPERATURE ABOUT PLUS 18.4C), WHICH SUPPORTS THE 
INITIAL POSITION AND RECENT TRACK MOTION WITH HIGH CONFIDENCE. THIS 
IMPROVED CORE STRUCTURE IS CLEARLY EVIDENT IN A 310908Z SSMIS 91GHZ 
COLOR COMPOSITE MICROWAVE IMAGE WITH SPIRAL BANDING PREDOMINANTLY 
OVER THE SOUTHERN SEMICIRCLE. TY 06W HAS TURNED NORTHWESTWARD AS IT 
COMES UNDER THE STEERING INFLUENCE OF THE DEEP-LAYER SUBTROPICAL 
RIDGE (STR) POSITIONED TO THE NORTH AND NORTHEAST WHILE MAINTAINING A 
FORWARD MOTION OF 08 KNOTS. THE 310000Z 500MB UPPER-AIR SOUNDINGS 
OVER WESTERN JAPAN AND SOUTH KOREA INDICATE EAST-SOUTHEASTERLY TO 
EASTERLY WINDS AT 15 TO 25 KNOTS WITH THE RIDGE AXIS EXTENDING FROM 
WESTERN JAPAN TO SOUTH KOREA. THE INITIAL INTENSITY OF 115 KTS IS 
ASSESSED WITH HIGH CONFIDENCE BASED ON AGENCY DVORAK ESTIMATES AS 
WELL AS THE CIMSS ADT ESTIMATE AND A 311200Z D-PRINT ESTIMATE OF 116 
KNOTS.

INITIAL WIND RADII BASIS: SMAP DATA (WESTERN SEMICIRCLE), 
SCATTEROMETER DATA (BULLSEYE) AND LIMITED SURFACE OBSERVATIONS.

CURRENT STEERING MECHANISM: DEEP-LAYER STR POSITIONED TO THE NORTH
AND NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T6.0 - 115 KTS
   KNES: T6.0 - 115 KTS
   CIMSS SATCON: 118 KTS AT 311011Z
   CIMSS ADT: 117 KTS AT 311130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL

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 06W WILL TRACK WEST-NORTHWESTWARD THROUGH
TAU 72 PASSING TO THE SOUTH OF OKINAWA WITH A PEAK INTENSITY OF
120 KNOTS BY TAU 12. GRADUAL WEAKENING SHOULD OCCUR AS THE SYSTEM 
PASSES OKINAWA WITH MORE PRONOUNCED WEAKENING AS IT SLOWS AND STALLS 
NORTHWEST OF OKINAWA AND UPWELLS COOLER WATER. THE 310600Z HAFS-A RUN 
INDICATES SIGNIFICANT UPWELLING OCCURRING WITH SEA SURFACE 
TEMPERATURES COOLING DOWN TO 21-22C NEAR THE CENTER, WHICH SHOULD 
PRODUCE A FAIRLY SHARP WEAKENING TREND. DUE TO THE SYSTEM'S LARGE 
SIZE AND CLOSE PROXIMITY TO OKINAWA AFTER CPA, THERE REMAINS A HIGH 
PROBABILITY OF GALE-FORCE WINDS OR HIGHER IF THE SYSTEM DRIFTS CLOSER 
WITHIN THE WEAK STEERING ENVIRONMENT. AS DISCUSSED BELOW, THERE IS 
HIGH UNCERTAINTY (LOW CONFIDENCE) IN THE JTWC FORECAST TRACK AFTER 
TAU 48.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE REMAINS IN GOOD
AGREEMENT ONLY THROUGH TAU 48 WITH A 44NM CROSS-TRACK SPREAD AT TAU
36 AND A 50NM CROSS-TRACK SPREAD AT TAU 48 LENDING HIGH CONFIDENCE
TO THIS PORTION OF THE JTWC FORECAST TRACK. JTWC FORECAST TRACKS HAVE
REMAINED WITHIN A TIGHT, 50NM ENVELOPE JUST TO THE SOUTH OF
OKINAWA OVER THE PAST FOUR DAYS. HOWEVER, ALONG-TRACK SPEEDS HAVE 
REMAINED INCONSISTENT RESULTING IN A SIGNIFICANT CHANGE IN THE CPA 
TIMING OVER THE PAST 18 HOURS. AFTER TAU 48, BOTH DETERMINISTIC AND
PROBABILISTIC GUIDANCE CONTINUE TO INDICATE A VERY LARGE SPREAD
(345NM SPREAD AT TAU 96 AND A 450NM SPREAD AT TAU 120) AND A HIGH
DEGREE OF UNCERTAINTY DUE TO THE RAPID WEAKENING OF THE STEERING
RIDGE TO THE NORTH. THIS RAPID WEAKENING OF THE STEERING RIDGE IS
DUE TO A COMBINATION OF THE WESTERLIES ACROSS THE KOREAN PENINSULA
AND THE UNUSUALLY LARGE SIZE OF TY 06W, WHICH IS CURRENTLY
ESTIMATED AT A 700-780NM DIAMETER. AFTER TAU 48, TY 06W WILL BE
POSITIONED WITHIN A COMPETING STEERING ENVIRONMENT WITH A STR TO
THE EAST AND ANOTHER WEAK STR TO THE WEST THUS A SLOW, POSSIBLY
ERRATIC TRACK THROUGH TAU 120. THIS UNCERTAIN SCENARIO IS EVIDENT
IN THE 310600Z ECMWF (EPS) AND GFS (GEFS) ENSEMBLE SOLUTIONS.

FORECAST CONFIDENCE:
   TRACK 0 - 48 HR: HIGH
   TRACK 48 - 120 HR: LOW
   INTENSITY 0 - 48 HR: HIGH
   INTENSITY 48 - 120 HR: MEDIUM//
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