Tropical Storm HAISHEN Advisory Tue Sep 08

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (HAISHEN)
WARNING NR 028//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 11W (HAISHEN), LOCATED APPROXIMATELY 119
NM NORTHEAST OF OSAN AB, SOUTH KOREA, HAS TRACKED NORTHWARD
AT 29 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL
SATELLITE IMAGERY (MSI) DEPICTS MID-LEVEL CONVECTION SHEARED
TO THE NORTHEAST OF THE LOW LEVEL CIRCULATION CENTER WHICH
HAS ENTERED THE SEA OF JAPAN. THE INITIAL POSITION IS PLACED
WITH FAIR CONFIDENCE BASED ON THE PARTIALLY EXPOSED LOW
LEVEL CIRCULATION IN THE MSI LOOP, AS WELL AS THE
REMAINING CONVECTIVE BANDING THAT CONTINUES TO WRAP INTO A
LOW LEVEL CIRCULATION FEATURE IN A 070426Z AMSR2 IMAGE. THE
INITIAL INTENSITY OF 60 KTS IS PLACED WITH FAIR CONFIDENCE
AND IS HEDGED SLIGHTLY BELOW MULTI-AGENCY DVORAK CURRENT
INTENSITY ESTIMATES OF T4.0 (65 KTS, RJTD AND PGTW) AND THE
64 KTS MAX WINDS PRESENT IN THE AMSR2 WIND PRODUCT DUE TO
THE WEAKENING NATURE OF THE CONVECTION. ENVIRONMENTAL
CONDITIONS REMAIN MARGINAL DUE TO HIGH (20+ KTS) VERTICAL
WIND SHEAR, COOL (22-23 CELSIUS) SEA SURFACE TEMPERATURES,
AND WEAKENING EQUATORWARD OUTFLOW. THE SYSTEM IS BEGINNING
EXTRATROPICAL TRANSITION AS IT IS BECOMING EMBEDDED IN THE
DEEP WESTERLY FLOW OF THE JET ALOFT. OF NOTE, THIS UPPER
LEVEL WESTERLY FLOW IS OFFSETTING THE UNFAVORABLE
ENVIRONMENTAL CONDITIONS SLIGHTLY, WHICH HAS LEAD TO ONLY
MODEST WEAKENING OVER THE PAST 6 HOURS. THE CYCLONE IS
CONTINUING TO TRACK ALONG THE WESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE (STR) TO THE EAST.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST
PHILOSOPHY FROM THE LAST PROGNOSTIC REASONING MESSAGE.
   B. TS HAISHEN WILL CONTINUE TO TRACK POLEWARD THROUGHOUT
THE REMAINDER OF THE FORECAST PERIOD UNDER THE STEERING
INFLUENCE OF THE STR. BY TAU 12, THE SYSTEM WILL MAKE A
SECOND LANDFALL OVER THE KOREAN PENINSULA. THE CONTINUED
UNFAVORABLE ENVIRONMENTAL CONDITIONS OF HIGH VERTICAL WIND
SHEAR, COOL SEA SURFACE TEMPERATURES WHILE OVER WATER AND
INTERACTION WITH UNDERLYING TERRAIN WHILE OVER LAND WILL
LEAD TO A DRAMATIC WEAKENING TO 35 KTS BY TAU 12, AT WHICH
TIME IT WILL HAVE BECOME FULLY EMBEDDED IN THE BAROCLINIC
ZONE AND COMPLETED EXTRATROPICAL TRANSITION. THE SYSTEM IS
EXPECTED TO ONLY SLIGHTLY WEAKEN THEREAFTER AS IT BECOMES
AS COLD CORE LOW OVER MANCHURIA. NUMERICAL MODEL SOLUTIONS
ARE IN FAIR AGREEMENT AFTER TAU 12 DUE TO THE SPREAD IN
TRACK GUIDANCE DUE TO THE INTERACTION OF THE SYSTEM WITH A
MAJOR SHORTWAVE TROUGH ALOFT, HOWEVER THERE IS STILL HIGH
CONFIDENCE IN THE OVERALL JTWC FORECAST TRACK THROUGH THE
REMAINDER OF THE FORECAST PERIOD.
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