Tropical Storm TEMBIN Advisory Wed Aug 22

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (TEMBIN) WARNING NR 15//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 15W (TEMBIN), LOCATED APPROXIMATELY 210 NM SOUTHEAST
OF TAIPEI, TAIWAN, HAS TRACKED WESTWARD AT 03 KNOTS OVER THE PAST
SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY SHOWS DEEP
CENTRALIZED CONVECTION OVER THE LOW LEVEL CIRCULATION CENTER (LLCC)
WITH SEVERAL IDENTIFIABLE BANDING FEATURES WRAPPING INTO THE LLCC.
RADAR IMAGERY FROM TAIWAN HAS BEEN USEFUL IN IDENTIFYING THE CURRENT
LOCATION OF THE LLCC AS THE CONVECTION OVER THE SYSTEM HAS MADE IT
DIFFICULT TO IDENTIFY IN THE LOOPING INFRARED IMAGERY. THE TRACK
SPEEDS HAVE BEEN DECREASING OVER THE PAST 12 HOURS AS THE PRIMARY
STEERING INFLUENCE, A DEEP LAYERED SUBTROPICAL RIDGE (STR) TO THE
NORTH, HAS BEEN WEAKENED BY A TRANSITING MID-LATITUDE TROUGH LOCATED
OVER THE KOREAN PENINSULA. UPPER LEVEL ANALYSIS INDICATES THE
POLEWARD OUTFLOW TOWARDS A TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT)
CELL LOCATED OVER SOUTHERN HONSHU HAS STARTED TO DIMINISH OVER THE
PAST SIX HOURS. THE TUTT CELL TO THE SOUTHWEST HAS ALSO STARTED TO
OUTPACE TY 15W TO THE WEST, CAUSING A REDUCTION IN EQUATORWARD
OUTFLOW TO THE SOUTHWEST. SEA SURFACE TEMPERATURES WITHIN THE REGION
REMAIN FAVORABLE (28 TO 30 CELSIUS) ALONG THE FORECAST TRACK. THE
CURRENT INTENSITY HAS BEEN DECREASED TO 85 KNOTS TO ACCOUNT FOR THE
OBSERVED DECREASE IN ORGANIZATION AS DVORAK ESTIMATES HAVE BEEN
STEADY OVER THE PAST 12 HOURS FROM PGTW. BASED ON RADAR IMAGERY,
THERE IS HIGH CONFIDENCE IN THE CURRENT POSITIONING AND INTENSITY
ESTIMATE.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 15W IS FORECAST TO TRACK WEST-NORTHWESTWARD UNDER THE
INFLUENCE OF THE DEEP STR THROUGH TAU 36. A MID-LATITUDE TROUGH OVER
EASTERN CHINA IS EXPECTED TO LIFT NORTHWARD ALLOWING FOR AN
EXTENSION OF THE STR TO BUILD WESTWARD, LINKING TO A SECOND STR
LOCATED OVER CENTRAL CHINA. THIS WILL TURN TY 15W TO THE WEST-
SOUTHWEST BY TAU 48. THE INTENSITY IS EXPECTED TO REMAIN STEADY
UNDER FAVORABLE SURFACE CONDITIONS WITH AMPLE UPPER LEVEL OUTFLOW
SUPPORT THROUGH THE NEXT 24 HOURS. BY TAU 30 TY 15W IS EXPECTED TO
MAKE LANDFALL WITH TAIWAN AND WILL QUICKLY WEAKEN TO LOW TYPHOON
STRENGTH BY THE TIME IT ENTERS THE TAIWAN STRAIT. DECREASING UPPER
LEVEL SUPPORT WILL SLOWLY WEAKEN THE SYSTEM BETWEEN TAU 48 AND 72.
   C. AFTER TAU 72, TY 15W WILL SLOWLY TRACK WEST-SOUTHWESTWARD AS
MODEL GUIDANCE INDICATES TY 16W (BOLAVEN) WILL APPROACH FROM THE
EAST, LEADING TO AN INCREASED BINARY INTERACTION. THIS INTERACTION
HAS MADE THE EXTENDED FORECAST DIFFICULT AS GUIDANCE HAS BECOME
HIGHLY SPREAD BEYOND TAU 48. WBAR CONTINUES TO INDICATE A CROSSING
OVER NORTHERN TAIWAN AND QUICKLY TRACKING INTO CHINA. GFS AND NGPS
INDICATE A LOOP TO THE SOUTH AND BACK TOWARDS THE APPROACHING TY
16W. GFDN QUICKLY TRACKS THE SYSTEM ACROSS SOUTHERN TAIWAN TOWARDS
HONG KONG AND INTO THE SOUTHERN PORTION OF THE SOUTH CHINA SEA.
ECMWF HAS SHIFTED TO A SOUTHERN LOOP SIMILAR TO NGPS WITHIN THE PAST
12 HOURS. THE CURRENT FORECAST IS BASED ON THE CONSENSUS THROUGH TAU
48, BUT THEN SLOWS THE SYSTEM DOWN IN THE NORTHERN SOUTH CHINA SEA,
AS THE EXPECTATION OF A STRONG BINARY INTERACTION AS DEPICTED IN
NGPS AND GFS DOES NOT SEEM LIKELY AS THE SEPARATION DISTANCE WILL BE
ON THE ORDER OF 500 NM BY TAU 72, AND WILL LIKELY INCREASE BEYOND
TAU 72. BASED ON THE HIGHLY VARIABLE MODEL GUIDANCE OVER THE PAST 12
HOURS, THERE IS LOW CONFIDENCE IN THE EXTENDED TRACK FORECAST.//
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