Tropical Storm TEMBIN Advisory Pzt, 27.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (TEMBIN) WARNING NR 32//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 15W (TEMBIN), LOCATED APPROXIMATELY 355 NM
SOUTHWEST OF TAIPEI, TAIWAN, HAS TRACKED SOUTHEASTWARD AT 06 KNOTS
OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY
INDICATES AN ONGOING WEAKENING TREND DUE TO INCREASING VERTICAL
WIND SHEAR ASSOCIATED WITH EQUATORWARD OUTFLOW FROM TY 16W. THIS
INTERACTION IS CLEARLY EVIDENT IN RECENT ANIMATED WATER VAPOR
IMAGERY. AS A RESULT OF THE EASTERLY VERTICAL WIND SHEAR,
CONVECTIVE ORGANIZATION HAS DEGRADED AND THE CENTER HAS BECOME MORE
DIFFICULT TO DISCERN IN SATELLITE IMAGERY; HOWEVER, RADAR FIXES ARE
AVAILABLE FROM MULTIPLE AGENCIES. THE INITIAL POSITION IS BASED ON
ANIMATED ENHANCED INFRARED IMAGERY AND AVAILABLE RADAR FIXES WITH
GOOD CONFIDENCE. THE INITIAL INTENSITY IS ASSESSED AT 85 KNOTS
BASED ON AN AVERAGE OF DVORAK INTENSITY ESTIMATES RANGING FROM 77
TO 90 KNOTS FROM PGTW AND RJTD, RESPECTIVELY. TY 15W IS LOCATED
WITHIN A WEAK STEERING ENVIRONMENT BETWEEN A WEAK SUBTROPICAL RIDGE
(STR) TO THE NORTH AND A BUILDING NEAR-EQUATORIAL RIDGE (NER) TO
THE SOUTH. ADDITIONALLY, THERE MAY BE SOME WEAK INTERACTION
OCCURRING WITH TY 16W, WHICH IS CENTERED APPROXIMATELY 695 NM EAST-
NORTHEAST OF TY 15W'S CENTER.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 15W IS FORECAST TO REMAIN WITHIN THIS WEAK STEERING
ENVIRONMENT THROUGH TAU 12 AND WILL TRACK INCREASINGLY
NORTHEASTWARD ALONG THE NORTHWESTERN PERIPHERY OF THE NER, WHICH IS
FORECAST TO BUILD TO THE EAST AS TY 16W TRACKS QUICKLY POLEWARD
INTO THE YELLOW SEA. THIS WILL ALLOW TY 15W TO TURN POLEWARD AND
ACCELERATE JUST EAST OF, OR POSSIBLY OVER TAIWAN. DYNAMIC MODEL
GUIDANCE IS IN POOR AGREEMENT WITH A 250+ NM SPREAD AT TAU 72. THE
JTWC FORECAST IS POSITIONED CLOSE TO THE MODEL CONSENSUS BUT FAVORS
THE ECMWF AND JGSM SOLUTIONS, WHICH HAVE BEEN VERY CONSISTENT. THE
GFS MODEL IS THE MAJOR OUTLIER, WITH A NORTHEASTERLY TRACK INTO THE
YELLOW SEA. TY 15W IS FORECAST TO GRADUALLY WEAKEN THOUGH TAU 48 DUE
TO ONGOING INTERACTION WITH LAND AND MODERATE VERTICAL WIND SHEAR.
THE INTENSITY FORECAST IS BASED ON AN EAST-OF-TAIWAN FORECAST,
HOWEVER, A SLIGHT WESTWARD SHIFT IN TRACK COULD FURTHER DEGRADE THE
INTENSITY. THE SYSTEM IS FORECAST TO MAKE LANDFALL SOUTHEAST OF
SHANGHAI, CHINA NEAR TAU 72.
  C. AFTER TAU 72, TY 15W IS FORECAST TO TRACK NORTHWARD ALONG THE
WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE TOWARD THE SHANGHAI
REGION. DYNAMIC MODEL GUIDANCE IS IN POOR AGREEMENT WITH A LARGE
SPREAD AT TAU 120. GFDN IS THE WESTERN-MOST OUTLIER WHEREAS GFS IS
NOW THE EASTERN-MOST OUTLIER WITH A POLEWARD TRACK OVER THE KOREAN
PENINSULA. THE JTWC FORECAST FAVORS THE ECMWF SOLUTION AND
REMAINS CONSISTENT WITH PREVIOUS WARNINGS. TY 15W IS EXPECTED TO
WEAKEN AS IT MOVES OVER LAND AND SHOULD DECREASE TO 30 TO 35 KNOTS
BY TAU 120. BASED ON THE COMPLEX AND WEAK STEERING PATTERN AS WELL
AS POSSIBLE WEAK INTERACTION WITH TY 16W, THERE IS LOW CONFIDENCE IN
THE FORECAST TRACK.//
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