Tropical Storm TEMBIN Advisory Sa, 25-08

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (TEMBIN) WARNING NR
22//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 15W (TEMBIN), LOCATED APPROXIMATELY 180 NM SOUTH-
SOUTHWEST OF TAIPEI, TAIWAN, HAS TRACKED WEST-SOUTHWESTWARD AT 10
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY SHOWS THE STRUCTURE OF THE LOW LEVEL CIRCULATION CENTER
(LLCC) HAS SUFFERED A SIGNIFICANT INFLOW ISSUE AS WINDS ALONG THE
SOUTHEASTERN QUADRANT TRACK OVER SOUTHERN TAIWAN. THE CURRENT
FORECAST HAS DROPPED THE INTENSITY TO A STRONG TROPICAL STORM AT 60
KNOTS BASED ON OBSERVATIONS IN TAIWAN AND FROM A RECENT 230200Z
ASCAT PASS SHOWING WINDS ALONG THE WESTERN HALF OF THE SYSTEM IN THE
35 TO 40 KNOT RANGE, WITH A BAND OF WINDS IN THE LUZON STRAIT
SHOWING 30 KNOTS. RECENT DVORAK ESTIMATES FROM PGTW REFLECTED A DT
OF 3.0 WITH A PT OF 4.0. THE 4.5 FT WAS LIMITED BY CONSTRAINTS.
GIVEN THIS ANALYSIS OF THE SYSTEM IN CONJUNCTION WITH THE PREVIOUSLY
MENTIONED ASCAT PASS AND OBSERVATIONS ON TAIWAN, THE INTENSITY WAS
DECREASED TO 60 KNOTS AS THE SYSTEM STRUGGLES TO REORGANIZE. UPPER
LEVEL ANALYSIS INDICATES THE EQUATORWARD OUTFLOW CHANNEL CONTINUES
TO PROVE AMPLE EXHAUST FOR THE SYSTEM, BUT THE POLEWARD CHANNEL HAS
SHOWN SIGNS OF WEAKENING. TS 15W IS TRACKING ALONG THE SOUTHWESTERN
EXTENSION OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) CENTERED OVER
THE EAST CHINA SEA. TY 16W (BOLAVEN) REMAINS OVER 700 NM AWAY, AND
DOES NOT APPEAR TO HAVE ANY NOTABLE EFFECT ON THE TRACK OF TS 15W AS
IT IS BEYOND THE TYPICAL THRESHOLD OF DIRECT CYCLONE INTERACTION.
3. FORECAST REASONING.
   A. THERE HAS BEEN A CHANGE IN THE INTENSITY FORECAST PHILOSOPHY
BASED ON THE RECENT WEAKENING BEING GREATER THAN PREVIOUSLY
FORECAST. THE NEW PHILOSOPHY INCORPORATES AN INITIALLY WEAKER SYSTEM
THAT STRENGTHENS OVER THE NEXT 48 HOURS, WEAKENING BEYOND.
   B. TS 15W WILL CONTINUE TO STEER IN A GENERAL WEST-SOUTHWESTWARD
DIRECTION WITHIN THE TAIWAN STRAIT FOR THE NEXT 36 HOURS, SLOWLY
INTENSIFYING IN A FAVORABLE SURFACE ENVIRONMENT WITH VENTING IN THE
UPPER LEVEL EQUATORWARD VENTING CHANNEL. AS THE MID-LATITUDE TROUGH
OVER MAINLAND CHINA INTENSIFIES, THE STR TO THE NORTH OF TS 15W WILL
WEAKEN, ALLOWING FOR A NEAR EQUATORIAL RIDGE TO BEGIN TRACKING THE
SYSTEM BACK TO THE EAST IN A COUNTER-CLOCKWISE LOOP THROUGH TAU 72.
   C. AFTER TAU 72, TS 15W IS EXPECTED TO ACCELERATE EAST-
NORTHEASTWARD AS THE NER AMPLIFIES. AS TY 16W (BOLAVEN) PASSES TO
THE NORTHEAST, SOME BINARY INTERACTION IS POSSIBLE. AN INCREASINGLY
UNFAVORABLE UPPER LEVEL ENVIRONMENT IS EXPECTED TO CAUSE WEAKENING
OF THE SYSTEM BEYOND TAU 72 THROUGH THE REMAINDER OF THE FORECAST
PERIOD AS UPPER-LEVEL OUTFLOW BEYOND TAU 72 WOULD DEPEND ON OUTFLOW
FROM TY 16W AND THE STRENGTH OF THE STR AS IT RE-ESTABLISHES ITSELF
BEHIND TY 16W. DYNAMIC MODEL GUIDANCE REMAINS IN FAIR AGREEMENT (ALL
INDICATING A LOOPING TRACK WITH THE EXCEPTION OF GFDN) WITHIN 72
HOURS. HOWEVER, THERE IS LARGE VARIATION IN THE FORECAST GUIDANCE
BEYOND TAU 72 DUE TO THE POSSIBILITY OF INTERACTION WITH TY 16W AND
THE VARIATION IN STR ORIENTATION. AS SUCH, THERE REMAINS LOW
CONFIDENCE IN THE EXTENDED FORECAST TRACK.//
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