Tropical Storm TEMBIN Advisory Wed Aug 29

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (TEMBIN) WARNING NR
43//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 15W (TEMBIN), LOCATED APPROXIMATELY 450 NM SOUTH-
SOUTHWEST OF SEOUL, SOUTH KOREA, HAS TRACKED NORTH-NORTHEASTWARD AT
12 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
SATELLITE IMAGERY SHOWS FLARING CENTRAL CONVECTION WHICH IS NOW
CONTAINED NORTH OF THE LOW-LEVEL CIRCULATION CENTER (LLCC), AS
EVIDENT IN THE 291152Z SSMIS 91 GHZ MICROWAVE IMAGE. THE CURRENT
POSITION IS BASED ON THE 37 GHZ CHANNEL IN THE SSMIS IMAGE WITH HIGH
CONFIDENCE. THE CURRENT INTENSITY IS MAINTAINED AT 50 KNOTS BASED ON
DVORAK INTENSITY ESTIMATES RANGING FROM 45 TO 55 KNOTS FROM PGTW AND
RJTD/KNES RESPECTIVELY. UPPER-LEVEL ANALYSIS INDICATES TS TEMBIN
CONTINUES TO TRACK INCREASINGLY POLEWARD OF A SUBTROPICAL RIDGE
(STR) AXIS THAT EXTENDS FROM CENTRAL JAPAN TO DIRECTLY OVER TAIWAN.
THE VERTICAL WIND SHEAR (VWS) COMPONENT HAS CHANGED FROM THE
PREVIOUS OUT-OF-PHASE EASTERLY VECTOR TO THE CURRENT IN-PHASE
SOUTHERLY VECTOR. EVEN THOUGH VWS HAS INCREASED TO MODERATE TO
STRONG (20-30 KNOTS) LEVELS THE 12 KNOT POLEWARD TRACK SPEEDS ARE
NOW IN-PHASE WITH THE VWS AND SLIGHTLY OFFSETTING ITS WEAKENING
EFFECT, AS EVIDENT BY THE MICROWAVE SIGNATURE. ANIMATED WATER VAPOR
IMAGERY SHOWS THE EQUATORWARD OUTFLOW HAS CEASED DUE TO THE DEEP
UPPER-LEVEL TROUGH OVER EASTERN CHINA AND CURRENTLY ONLY THE
POLEWARD CHANNEL IS VENTING THE SYSTEM. TS 15W IS CURRENTLY STEERING
NORTHWARD IN BETWEEN THE WESTERN PERIPHERY OF THE DEEP-LAYERED STR
AND EASTERN PERIPHERY OF THE DEEP LONGWAVE TROUGH.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 15W IS FORECAST TO TRACK NORTHEASTWARD THROUGH TAU 12 UNDER
THE INFLUENCE OF THE STR AND LONGWAVE TROUGH. AFTER TAU 12 THE LLCC
WILL TRACK MORE EASTWARD AS THE STR SHIFTS IN RESPONSE TO THE
REMNANTS OF EXTRA-TROPICAL STORM 16W (BOLAVEN) TRACKING TO THE NORTH
OF THE STR. TS 15W WILL BEGIN TO WEAKEN BY TAU 12 AS IT APPROACHES
LANDFALL OVER THE SOUTHWESTERN TIP OF THE KOREAN PENINSULA DUE TO
VERY STRONG VWS AND COOLER SEA SURFACE TEMPERATURES (< 26C). THE
COMBINATION OF THE PREVIOUSLY MENTIONED ENVIRONMENTAL FACTORS
COUPLED WITH THE ADVECTION OF THE CONTINENTAL POLAR AIR MASS WILL
INITIATE AN EXTRA-TROPICAL TRANSITION (ETT) DURING THIS TIME. DURING
TAU 24 THE LLCC WILL DETERIORATE DUE TO FRICTIONAL EFFECTS AND ETT
WILL BE COMPLETE BY TAU 36 AS THE SYSTEM EXITS THE KOREAN PENINSULA
INTO THE SEA OF JAPAN. OBJECTIVE AID GUIDANCE IS IN EXCELLENT
AGREEMENT IN TERMS OF THE LANDFALL POSITION WITH ONLY A 35 NM SPREAD
BETWEEN THE LEFTMOST (WBAR) AND RIGHTMOST (GFDN) OUTLIERS. THE
OFFICIAL TRACK FORECAST IS KEPT SLIGHTLY FASTER THAN THE MODEL
CONSENSUS TO OFFSET THE HIGHLY UNLIKELY GFDN TRACKER BACK WEST INTO
THE YELLOW SEA. THERE IS HIGH CONFIDENCE IN THE TRACK FORECAST BASED
ON TIGHT MODEL GROUPING.//
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