Tropical Storm HAISHEN Advisory Sat Sep 05

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (HAISHEN) WARNING NR
019//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 11W (HAISHEN), LOCATED APPROXIMATELY 273 NM EAST-
SOUTHEAST OF KADENA AB, OKINAWA, HAS TRACKED NORTHWESTWARD AT 09 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS
THE SYSTEM HAS MAINTAINED A WELL-DEFINED 28-NM ROUND EYE. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EYE FEATURE. THE
INITIAL INTENSITY OF 125 KTS IS BASED ON AN OVERALL ASSESSMENT OF MULTI-
AGENCY DVORAK ESTIMATES RANGING FROM T6.0 (115 KTS) TO T6.5 (127 KTS)
AND REFLECTS THE WEAKENING TREND. TY 11W IS STILL IN AN OVERALL
FAVORABLE ENVIRONMENT WITH LOW (05-10KT) NORTHEASTERLY VERTICAL WIND
SHEAR (VWS), EXCELLENT RADIAL OUTFLOW, AND WARM (30-31C) SEA SURFACE
TEMPERATURES (SST). HOWEVER, A MAJOR SHORTWAVE TROUGH APPROACHING FROM
THE NORTHWEST IS BEGINNING TO CAUSE SUBSIDENCE AND EROSION ALONG THE
NORTHWEST QUADRANT. THE CYCLONE IS TRACKING UNDER THE STEERING INFLUENCE
OF THE DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTHEAST, NOW EAST-
SOUTHEAST OF HOKKAIDO, JAPAN.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE LAST PROGNOSTIC REASONING MESSAGE.
   B. THE APPROACHING SHORTWAVE TROUGH WILL WEAKEN THE STEERING STR AND
ALLOW TY 11W TO TRACK MORE NORTH-NORTHWESTWARD, PASS JUST TO THE WEST OF
KYUSHU, JAPAN, ACROSS THE KOREA STRAIT, MAKE LANDFALL JUST SLIGHTLY WEST
OF BUSAN, SOUTH KOREA SHORTLY AFTER TAU 48, THEN DRAG NORTHWARD ALONG
THE RUGGED MOUNTAIN RANGES OF THE KOREAN PENINSULA. INCREASING VWS,
COOLING SSTS, AND EVENTUALLY, LAND INTERACTION WILL GRADUALLY THEN
RAPIDLY ERODE THE SYSTEM, AND BY TAU 72 WILL BE REDUCED TO 30 KTS AFTER
IT CROSSES INTO NORTH KOREA. CONCURRENTLY, THE CYCLONE WILL BEGIN EXTRA-
TROPICAL TRANSITION AROUND TAU 48 AS IT ENTERS THE BAROCLINIC ZONE AND
TRANSFORM INTO A COLD CORE LOW BY TAU 72. NUMERICAL MODELS REMAIN IN
TIGHT AGREEMENT WITH JGSM AND ECMWF OUTLYING TO THE RIGHT OF THE MAIN
PACK BEYOND TAU 36. THERE IS OVERALL HIGH CONFIDENCE IN THE JTWC TRACK
FORECAST THAT IS LAID JUST LEFT OF THE MULTI-MODEL CONSENSUS BEYOND TAU
36 TO OFFSET THE OUTLIERS.//
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