Tropical Storm TEMBIN Advisory Su, 19-08

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 15W (FIFTEEN)
WARNING NR 01//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 15W (TEMBIN), LOCATED APPROXIMATELY 280 NM
NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED SOUTHWARD AT 05 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) AND AN 182203Z SSMIS 91 GHZ MICROWAVE IMAGE SHOW TIGHTLY
CURVED, DEEPLY CONVECTIVE BANDING AROUND A WELL-DEFINED LOW-LEVEL
CIRCULATION CENTER (LLCC). THE CURRENT POSITION IS BASED ON AN
EXTRAPOLATION FROM THE 37 GHZ CHANNEL OF THE SSMIS IMAGE AND AN
APPARENTLY VISIBLE LLCC IN THE MSI, WITH GOOD CONFIDENCE. THE
CURRENT INTENSITY IS BASED ON DVORAK ESTIMATES OF 30 KNOTS FROM PGTW
AND RJTD ALONG WITH 25-30 KNOTS OBSERVED IN THE 181548Z OSCAT PASS.
UPPER-LEVEL ANALYSIS INDICATES THE SYSTEM IS LOCATED A COUPLE
DEGREES POLEWARD OF THE NEAR EQUATORIAL RIDGE (NER) AXIS.
ADDITIONALLY, THE MULTIPLE SMALL TROPICAL UPPER-TROPOSPHERIC TROUGH
(TUTT) CELLS THAT PREVIOUSLY EXISTED A FEW DEGREES NORTH AND
NORTHWEST OF THE LLCC HAVE SINCE PROPAGATED FURTHER TO THE WEST.
THIS HAS ALLOWED FOR THE CONVERGENCE IN THE AREA TO WEAKEN AND IS
EVIDENT BY THE MSI SHOWING DEEP CONVECTION BEGINNING TO BUILD OVER
THE NORTHWESTERN PORTION OF THE LLCC, WHEREAS BEFORE IT WAS LACKING
IN THIS SECTOR. EQUATORWARD OUTFLOW IS MODERATE AND A SLIGHT
CONNECTION OF OUTFLOW TO THE EAST INTO A LARGER TUTT CELL IS ALSO
NOTICEABLE. TD 15W IS CURRENTLY IN A WEAK STEERING ENVIRONMENT AS
EVIDENT FROM PAST MOTION. THE SYSTEM HAS EXHIBITED SLOW EQUATORWARD
DRIFT OVER THE PAST 48 HOURS AS IT RESIDES NEAR THE WESTERN EDGE OF
THE TUTT AND AN EXTENSION OF THE NER.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST
PHILOSOPHY.
   B. TD 15W SHOULD CONTINUE TO SLOWLY DRIFT SOUTHWARDS DURING THE
NEXT 12 HOURS. BY TAU 24 THE NARROW WESTERN EXTENSION OF THE LOW- TO
MID-LEVEL NER SHOULD BEGIN TO STEER THE SYSTEM ON A MORE POLEWARD
TRACK. OVER THE NEXT FEW DAYS TD 15W SHOULD CONTINUE THIS POLEWARD
TRACK AS THE EXTENSION OF THE NER BUILDS IN. GRADUAL INTENSIFICATION
IS EXPECTED UNDER FAVORABLE UPPER-LEVEL ENVIRONMENTAL CONDITIONS,
SUCH AS WEAK TO MODERATE VWS, WARM SEA SURFACE TEMPERATURES (26-30
DEGREES CELSIUS), AND IMPROVING OUTFLOW. BY TAU 72, AS THE SYSTEM
INTENSIFIES, IT SHOULD COME UNDER THE STEERING INFLUENCE OF THE
SOUTHWESTERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR),
CENTERED EAST OF JAPAN, AND BEGIN TO DEFLECT WESTWARD TOWARDS TAIWAN.
   C. IN THE EXTENDED FORECAST TD 15W SHOULD CONTINUE TO BE STEERED
BY THE SOUTHWESTERN PERIPHERY OF THE STR AND CONTINUE TO TRACK
WESTWARD WHERE LANDFALL OVER TAIWAN IS EXPECTED SHORTLY AFTER TAU 96
AS A SIGNIFICANT TYPHOON. BY TAU 120, TD 15W SHOULD EMERGE OFF THE
WESTERN COAST OF TAIWAN INTO THE TAIWAN STRAIT WHERE IT WILL
CONTINUE TO TRACK WESTWARD TOWARDS EASTERN CHINA. THE SYSTEM SHOULD
BE ABLE TO REFORM AFTER THE BRIEF INTERACTION WITH LAND AND IS
EXPECTED TO BE SLIGHTLY WEAKENED BY THIS INTERACTION. THE OBJECTIVE
AID GUIDANCE IS SPILT BETWEEN A SOUTHWESTWARD TURN AND A
SOUTHEASTWARD TURN. BASED ON PREVIOUS TRACK MOTION AND SYNOPTIC
ENVIRONMENT THE SOUTHWESTWARD TURN WAS FAVORED. AFTER THE SYSTEM HAS
MADE ITS LOOP POLEWARD THE GUIDANCE IS IN GENERALLY FAIR AGREEMENT
IN A TRACK TOWARDS TAIWAN. HOWEVER, THE NOGAPS IS AN OUTLIER WITH A
TRACK TOWARDS THE LUZON STRAIT AND THE GFS TRACKS CLOSER TO
SHANGHAI. DUE TO THE INITIAL WEAK STEERING ENVIRONMENT AND
UNCERTAINTY IN THE TIMING OF FUTURE STEERING INFLUENCES, CONFIDENCE
IN THE TRACK FORECAST IS LOW.//
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