Tropical Storm WUTIP Advisory Su, 29-09

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (WUTIP) WARNING NR
07//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 20W (WUTIP), LOCATED APPROXIMATELY 337 NM EAST OF
DA NANG, VIETNAM, HAS TRACKED NORTHWARD AT 03 KNOTS OVER THE PAST
SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) INDICATES
THAT TS 20W HAS BECOME QUASI-STATIONARY AND HAS CONTINUED TO
INCREASE IN CONVECTIVE ORGANIZATION AS THE CENTRAL DENSE OVERCAST
FEATURE HAS PERSISTED AND DEEPENED OVER THE LOW-LEVEL CIRCULATION
CENTER (LLCC). A 280522Z AMSU-B MICROWAVE IMAGE DEPICTS A TIGHTLY
WRAPPED STRUCTURE WITH DEEP CONVECTION PERSISTING OVER THE LLCC AND
IMPROVED CONVECTIVE BANDING LOCATED PRIMARILY OVER THE NORTHERN SEMI-
CIRCLE. THERE IS GOOD CONFIDENCE IN THE INITIAL POSITION AND RECENT
MOTION BASED ON THE MSI AND THE AFOREMENTIONED MICROWAVE IMAGE. THE
INITIAL INTENSITY HAS BEEN INCREASED TO 60 KNOTS BASED ON THE
IMPROVING STRUCTURE AND AN AVERAGE OF DVORAK INTENSITY ESTIMATES
FROM PGTW AND KNES THAT RANGE FROM 55 TO 65 KNOTS. UPPER-LEVEL
ANALYSIS AND ANIMATED WATER VAPOR IMAGERY SHOWS A FAVORABLE
ENVIRONMENT WITH DUAL CHANNEL OUTFLOW AND LOW TO MODERATE (10 TO 20
KNOTS) VERTICAL WIND SHEAR. TS 20W IS MEANDERING IN A WEAK STEERING
ENVIRONMENT AS THE SUBTROPICAL STEERING RIDGE (STR) HAS BROKE DOWN
IN RESPONSE TO THE DIGGING TROUGH THAT IS CURRENTLY OVER EASTERN
CHINA.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 20W IS FORECAST TO TRACK SLOWLY WESTWARD TO WEST-
SOUTHWESTWARD THROUGH TAU 24 UNDER THE WEAK STEERING INFLUENCE OF
THE REBUILDING STR. AFTER TAU 24, THE SYSTEM IS EXPECTED TO
GRADUALLY ACCELERATE WESTWARD AS THE STR BECOMES MORE ESTABLISHED
AND THE SHORTWAVE TROUGH PROPAGATES TO THE EAST. TS 20W WILL
CONTINUE TO INTENSIFY TO A PEAK INTENSITY OF 85 KNOTS PRIOR TO
LANDFALL DUE TO GENERALLY FAVORABLE ENVIRONMENTAL CONDITIONS. TS 20W
IS FORECAST TO MAKE LANDFALL OVER VIETNAM SHORTLY AFTER TAU 48 AND
WILL BEGIN TO DISSIPATE DUE TO THE LAND INTERACTION.
   C. IN THE EXTENDED PERIOD, TS 20W IS FORECAST TO DISSIPATE OVER
LAND. NUMERIC MODEL GUIDANCE HAS COME INTO TIGHTER AGREEMENT WITH
ONLY A 100NM SPREAD BY TAU 48 AND ONLY SLIGHT DIFFERENCES IN TRACK
SPEED. OVERALL, HIGH CONFIDENCE REMAINS IN THE JTWC FORECAST TRACK.//
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