Tropical Storm HAISHEN Advisory Sat Sep 05

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 11W (HAISHEN) WARNING NR
016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   SUPER TYPHOON (STY) 11W (HAISHEN), LOCATED APPROXIMATELY 439 NM
SOUTHEAST OF KADENA AB, OKINAWA, HAS TRACKED NORTHWESTWARD AT 09 KNOTS
(KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY REVEALS A WELL-DEFINED, 31 NM ROUND EYE WHICH SUPPORTS THE
INITIAL POSITION WITH HIGH CONFIDENCE. A 040619Z SSMI COMPOSITE
MICROWAVE IMAGE DEPICTS A COMPACT EYEWALL (80 NM IN DIAMETER) WITH A
DEVELOPING, FRAGMENTED SECONDARY EYEWALL TO THE EAST AND SPIRAL
BANDING WRAPPING IN FROM THE SOUTH. THE CIMSS M-PERC PRODUCT INDICATES
THAT THERE IS A 60-70% CHANCE THAT STY 11W WILL UNDERGO AN EYEWALL
REPLACEMENT CYCLE AS IT PROGRESSES. BASED ON DVORAK CURRENT INTENSITY
ESTIMATES RANGING FROM T6.5 (127 KTS) TO T7.0 (140 KTS) AND A 040442Z
SATCON ESTIMATE OF 130 KTS, THE INITIAL INTENSITY IS SET AT 135 KTS
WITH GOOD CONFIDENCE. TY 11W IS TRANSITING THROUGH A HIGHLY FAVORABLE
ENVIRONMENT CHARACTERIZED BY LOW VERTICAL WIND SHEAR (VWS), RADIAL
OUTFLOW, WARM (30-31 CELSIUS) SEA SURFACE TEMPERATURES (SST), AND
CONDUCIVE OCEAN HEAT CONTENT VALUES. THE 04/0000Z 500MB ANALYSIS SHOWS
A DEEP MIDLATITUDE SHORTWAVE TROUGH OVER THE EAST CHINA SEA AND
WESTERN JAPAN WITH A BROAD SUBTROPICAL RIDGE (STR) ENTRENCHED NORTH OF
THE SYSTEM. ADDITIONALLY, THERE IS A WEAK STR EXTENSION EXTENDING
SOUTHWESTWARD FROM THE STR. STY 11W IS TRACKING WEST-NORTHWESTWARD
UNDER THE STEERING INFLUENCE OF THE DEEP-LAYERED STR AND IS TRACKING
TOWARD A COL REGION POSITIONED SOUTH OF OKINAWA.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE LAST PROGNOSTIC REASONING MESSAGE.
   B. IN THE NEAR-TERM, THE STR IS FORECAST TO BUILD, REMAINING
STATIONARY OVER JAPAN AS THE SHORTWAVE TROUGH GRADUALLY FILLS OVER THE
KOREAN PENINSULA. NUMERICAL MODEL GUIDANCE HAS COME INTO BETTER
AGREEMENT NEAR OKINAWA WITH A SPREAD OF 42 NM NEAR TAU 36. THE CURRENT
FORECAST TRACK REMAINS HIGHLY CONSISTENT WITH THE PREVIOUS FORECAST
AND INDICATES A NORTH-NORTHWESTWARD TRACK OVER AMAMI OSHIMA. AT TAU
72, THE SYSTEM IS FORECAST TO TRACK JUST WEST OF KYUSHU. THIS IS
SUPPORTED BY THE 04/00Z ECMWF ENSEMBLE; HOWEVER, DUE TO UNCERTAINTY IN
THE MODELS AND A 100 NM SPREAD AT TAU 72, THE SYSTEM COULD TRACK
CLOSER TO SASEBO / KYUSHU. THROUGH TAU 36, STY 11W IS EXPECTED TO
MAINTAIN SUPER TYPHOON INTENSITY. AFTERWARDS, THE SYSTEM WILL
GRADUALLY WEAKEN AS IT TRACKS POLEWARD.
   C. IN THE EXTENDED PERIOD, NUMERICAL MODEL GUIDANCE DIVERGES WITH
INCREASING UNCERTAINTY IN THE EXACT TRACK OVER SOUTH KOREA. NAVGEM, A
NOTABLE OUTLIER, TRACKS THE SYSTEM FURTHER WEST THAN THE MAJORITY OF
THE MODEL SOLUTIONS. AROUND TAU 72, THE SYSTEM IS FORECAST TO BEGIN
EXTRATROPICAL TRANSITION (ETT) AS IT INTERACTS WITH THE SHORTWAVE
TROUGH. THROUGHOUT THIS TRANSITION, THE SYSTEM WILL ACCELERATE
POLEWARD AND SIGNIFICANTLY WEAKEN AS IT TRANSITS OVER THE KOREAN
PENINSULA DUE TO INCREASING VWS AND INTERACTION WITH THE MOUNTAINOUS
TERRAIN. ETT COMPLETION IS EXPECTED BY TAU 96 AS THE SYSTEM GAINS
FRONTAL CHARACTERISTICS AND NEARS THE JET. OVERALL, THERE IS MODERATE
CONFIDENCE IN THE JTWC FORECAST TRACK WHICH IS PLACED NEAR THE MULTI-
MODEL CONSENSUS.//
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