Tropical Storm TEMBIN Advisory 27.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (TEMBIN) WARNING NR 33//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 15W (TEMBIN), LOCATED APPROXIMATELY 320 NM
SOUTHWEST OF TAIPEI, TAIWAN, HAS TRACKED EASTWARD AT 05 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) INDICATES THE PRIOR WEAKENING TREND HAS LEVELED OFF AND
CONVECTION IS RE-BUILDING OVER THE LOW LEVEL CIRCULATION CENTER
(LLCC). ALTHOUGH THE NORTHEASTERLY VERTICAL WIND SHEAR (VWS)
ASSOCIATED WITH EQUATORWARD OUTFLOW FROM TY 16W HAS EASED, ITS
EFFECTS ARE STILL SEEN IN MSI AND ANIMATED WATER VAPOR IMAGERY.
ADDITIONALLY, A MID-LATITUDE TROUGH APPROACHING FROM THE NORTH IS
PUTTING PRESSURE ON THE POLEWARD OUTFLOW. THE INITIAL POSITION IS
BASED ON ANIMATED MSI AND A 262212Z CORIOLIS 37GHZ MICROWAVE IMAGE
WITH GOOD CONFIDENCE. THE INITIAL INTENSITY IS ASSESSED AT 80 KNOTS
BASED ON AN AVERAGE OF DVORAK INTENSITY ESTIMATES OF 77 KNOTS FROM
PGTW AND RJTD, AND TAKING INTO ACCOUNT THE IMPROVING CONVECTION. 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
685 NM 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 MOVE INTO A MORE PRONOUNCED STEERING
ENVIRONMENT, 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 WEST OF THE MODEL CONSENSUS, FAVORING
THE ECMWF AND JGSM SOLUTIONS, WHICH HAVE BEEN VERY CONSISTENT. THE
GFS MODEL IS THE MAJOR EASTERN OUTLIER, WITH A NORTHEASTWARD TRACK
INTO THE YELLOW SEA. TY 15W IS FORECAST TO GRADUALLY WEAKEN THOUGH
TAU 36 DUE TO ONGOING INTERACTION WITH LAND. THE INTENSITY FORECAST
IS BASED ON AN EAST-OF-TAIWAN FORECAST SCENARIO, HOWEVER, A SLIGHT
WESTWARD SHIFT IN TRACK COULD FURTHER DEGRADE THE INTENSITY. THE
SYSTEM IS FORECAST TO SKIRT THE COAST SOUTHEAST OF SHANGHAI, CHINA
NEAR TAU 72.
  C. AFTER TAU 72, TY 15W IS FORECAST TO TRACK NORTH-NORTHWESTWARD
ALONG THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE. DYNAMIC MODEL
GUIDANCE IS IN POOR AGREEMENT, WITH A LARGE SPREAD AT TAU 120. GFDN
IS THE WESTERN-MOST OUTLIER WHEREAS GFS REMAINS THE EASTERN-MOST
OUTLIER, WITH A FASTER TRANSLATION SPEED RESULTING IN A
NORTHEASTWARD TRACK OVER THE KOREAN PENINSULA. THE JTWC FORECAST
FAVORS THE ECMWF SOLUTION AND REMAINS CONSISTENT WITH PREVIOUS
WARNINGS. TY 15W IS EXPECTED TO WEAKEN SLOWLY DUE TO INTERACTION
WITH LAND AND SHOULD DECREASE TO 30 TO 35 KNOTS BY TAU 120. BASED ON
THE COMPLEX STEERING PATTERN, UNCERTAINTIES IN THE LAND INTERACTION
WITH TAIWAN, AS WELL AS LARGE MODEL SPREAD, THERE IS LOW CONFIDENCE
IN THE FORECAST TRACK.//
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