Tropical Storm TEMBIN Advisory Mo, 20-08

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 15W (TEMBIN)
WARNING NR 02//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 15W (TEMBIN), LOCATED APPROXIMATELY 280 NM
NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED SOUTHEASTWARD AT 03
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) SHOWS OVER THE PAST SIX HOURS THE DEEP CONVECTIVE
BANDING HAS STARTED TO ENCOMPASS THE ENTIRE LOW LEVEL CIRCULATION
CENTER (LLCC). THE CURRENT INTENSITY HAS BEEN INCREASED TO TROPICAL
STORM STRENGTH, 35 KNOTS, BASED ON A 2.5/2.5 DVORAK ESTIMATE FROM
PGTW WITH A 3.0/3.0 FROM RJTD. KNES WAS SLIGHTLY WEAKER AT A 2.0/2.0
BUT INDICATED A DT OF 3.0 AT 190232Z. A 190203Z ASCAT PASS MISSED
THE PRIMARY LLCC, CATCHING THE FAR WESTERN EXTENT OF THE
CIRCULATION, AND INDICATED 25 TO 30 KNOTS. THE CURRENT POSITION IS
BASED ON THE WELL DEFINED LLCC OBSERVED IN MSI, WITH GOOD
CONFIDENCE. UPPER LEVEL ANALYSIS INDICATES TS 15W IS LOCATED SEVERAL
DEGREES NORTH OF A NEAR EQUATORIAL RIDGE (NER) WITH A WEAK EXTENSION
OF THE NER TO THE EAST AND A MINOR TROPICAL UPPER TROPOSPHERIC
TROUGH (TUTT) CELL DEVELOPING TO THE WEST OF TS 15W, WHICH IS
EVIDENT IN ANIMATED WATER VAPOR IMAGERY. THE NER IS PROVIDING AMPLE
EQUATORWARD OUTFLOW WITH INCREASING WESTWARD OUTFLOW INTO THE TUTT
CELL. THE TRACK HAS SLOWED OVER THE PAST SIX HOURS WITHIN A
WEAKENING STEERING ENVIRONMENT.
3. FORECAST REASONING.
   A. THE SHORT TERM FORECAST PHILOSOPHY HAS SHIFTED TO AN EASTWARD
LOOP BASED ON MSI SHOWING THE LLCC HAS BEEN TRACKING SOUTHEASTWARD
VICE THE PREVIOUS FORECAST INDICATING A SOUTHWESTWARD TURN. THE
EXTENDED FORECAST REMAINS CONSISTENT WITH THE PREVIOUS PROGNOSTIC
REASONING MESSAGE.
   B. TS 15W IS FORECAST TO REMAIN IN A WEAK STEERING ENVIRONMENT
OVER THE NEXT 12 TO 24 HOURS AS A NER TO THE SOUTHEAST OF TS 15W
BEGINS TO BUILD NORTHWESTWARD CAUSING THE SYSTEM TO START TRACKING
NORTHWARD. AS TS 15W MOVES NORTHWARD, THE SOUTHWESTERN EXTENT OF A
DEEP LAYERED SUBTROPICAL RIDGE (STR) LOCATED EASTWARD OF HONSHU,
JAPAN WILL CAUSE A SLIGHT NORTHWESTWARD SHIFT BETWEEN TAU 36 AND 48.
THE WESTWARD TURN WILL BECOME MORE PRONOUNCED BETWEEN TAU 48 AND 72.
STEADY INTENSIFICATION IS EXPECTED WITHIN A FAVORABLE ENVIRONMENT AS
SEA SURFACE TEMPERATURES REMAIN ABOVE 28 CELSIUS, EQUATORWARD
OUTFLOW PERSISTS IN VENTING THE SYSTEM AND VERTICAL WIND SHEAR
REMAINS LOW (5 TO 10 KNOTS).
   C. IN THE EXTENDED FORECAST TS 15W SHOULD CONTINUE TO BE STEERED
BY THE SOUTHWESTERN PERIPHERY OF THE STR AND CONTINUE TRACKING
WESTWARD, MAKING LANDFALL IN TAIWAN SLIGHTLY AFTER TAU 96. TRACKING
OVER TAIWAN, THE SYSTEM IS EXPECTED TO BE WITHIN THE TAIWAN STRAIT
BY TAU 120. INTENSITY IS FORECAST TO DECREASE AS IT TRACKS OVER
TAIWAN, EMERGING AS A STRONG TROPICAL STORM. DYNAMIC MODEL GUIDANCE
IS IN POOR AGREEMENT WITH NGPS SHOWING A SOUTHWESTWARD LOOP
EVENTUALLY TRACKING THE TS 15W TOWARDS A SECONDARY LLCC DEVELOPING
TO THE WEST OF GUAM. GFS REMAINS WELL TO THE NORTH OF TAIWAN AND
GFDN IS SLOW AND TRACKS WELL SOUTH OF TAIWAN. THE CURRENT FORECAST
IS SLIGHTLY FASTER THAN CONCENSUS TO ACCOUNT FOR NGPS BEING
COMPLETELY OPPOSITE OF THE MAJORITY OF AVAILABLE GUIDANCE, YET IT
ALSO ACCOUNTS FOR GFS BEING THE NORTHERN OUTLIER WITH SIGNIFICANTLY
FASTER TRACK SPEEDS. THE TRACK ITSELF IS IN LINE WITH ECMWF;
HOWEVER, IT IS SLOWER TO ACCOUNT FOR UNCERTAINTY IN THE STEERING
MECHANISM IN LATER TAUS. CURRENTLY THERE IS LOW CONFIDENCE IN THE
FORECAST TRACK BASED ON THE WEAK STEERING ENVIRONMENT.//
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