Tropical Storm TEMBIN Advisory Su, 26-08

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (TEMBIN) WARNING NR 26//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 15W (TEMBIN), LOCATED APPROXIMATELY 265 NM SOUTHWEST
OF TAIPEI, TAIWAN, HAS TRACKED WEST-SOUTHWESTWARD AT 04 KNOTS OVER
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS
TIGHTLY-CURVED CONVECTIVE BANDING WRAPPING INTO A WELL-DEFINED LOW-
LEVEL CIRCULATION CENTER (LLCC). DESPITE SOME WEAKENING OF
CONVECTIVE BANDING OVER LAND, A 250736Z SSMI IMAGE CONTINUES TO
DEPICT A WELL-ORGANIZED LOW-LEVEL CIRCULATION CENTER WITH A
SYMMETRIC EYEWALL SURROUNDING A MICROWAVE EYE FEATURE. THERE IS GOOD
CONFIDENCE IN THE INITIAL POSITION BASED ON THE DEFINED LLCC AND
RADAR FIXES FROM TAIWAN. THE INITIAL INTENSITY IS ASSESSED AT 75
KNOTS BASED ON DVORAK CURRENT INTENSITY ESTIMATES OF 77 KNOTS FROM
PGTW AND RJTD. TY 15W IS LOCATED WITHIN A WEAK STEERING ENVIRONMENT
BUT IS BEGINNING TO WEAKLY INTERACT WITH TY 16W AND DRIFT SLOWLY IN
A COUNTER-CLOCKWISE MOTION. THE 25/00Z 500MB ANALYSIS SHOWS THAT THE
SYSTEM IS LOCATED SOUTH OF A WEAKNESS IN THE SUBTROPICAL RIDGE (STR)
AND POLEWARD OF THE NEAR-EQUATORIAL RIDGE (NER). TY 15W'S CENTER IS
CURRENTLY ABOUT 760 NM WEST OF TY 16W'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 48 AND WILL TRACK INCREASINGLY EASTWARD
ALONG THE NORTHERN PERIPHERY OF THE NER WITH WEAK BINARY INTERACTION
POSSIBLE AS WELL. AFTER TAU 48, THE NER IS FORECAST TO BUILD TO THE
EAST AS TY 16W TRACKS QUICKLY POLEWARD INTO THE YELLOW SEA. THIS
WILL ALLOW TY 15W TO TURN AND ACCELERATE NORTHWARD OVER, OR PERHAPS
JUST EAST OF TAIWAN. WITH THE EXCEPTION OF GFDN, DYNAMIC MODEL
GUIDANCE IS IN GOOD AGREEMENT WITH A 170 NM SPREAD AT TAU 72. THE
JTWC FORECAST IS POSITIONED CLOSE TO BUT EAST OF THE MODEL CONSENSUS
TO OFFSET GFDN'S UNLIKELY TRACK OVER EASTERN CHINA. TY 15W IS
FORECAST TO INTENSIFY THROUGH TAU 36 BUT WILL WEAKEN PRIMARILY DUE
TO LAND INTERACTION AND POSSIBLY SOME INCREASED VERTICAL WIND SHEAR
DUE TO THE PROXIMITY OF TY 16W (ABOUT 650-700 NM AT TAU 36-48).
   C. AFTER TAU 72, TY 15W IS FORECAST TO TRACK NORTHWARD ALONG THE
WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE TOWARD THE SHANGHAI
REGION. THE BULK OF THE DYNAMIC MODEL GUIDANCE IS IN TIGHT AGREEMENT
WITH A 150 NM SPREAD AT TAU 120 (INCLUDING GFDN); GFS, HOWEVER, IS
THE SOLE OUTLIER WITH A POLEWARD TRACK FURTHER EAST ALONG 125E. TY
15W IS EXPECTED WEAKEN SLOWLY DUE TO INTERACTION WITH LAND AND
SHOULD DECREASE TO 55 TO 65 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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