Tropical Storm VAMCO Advisory dom, 15-11

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 25W (VAMCO) WARNING NR 021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 25W (VAMCO), LOCATED APPROXIMATELY 110 NM EAST OF
DA NANG, VIETNAM, HAS TRACKED WESTWARD AT 11 KNOTS OVER THE PAST SIX
HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS SIGNS OF
WEAKENING AS CONVECTIVE TOPS OVER THE EYE WALL, THAT HAS SINCE ENLARGED
TO 30NM, WARMED AND BECAME MORE RAGGED AND ASYMMETRIC. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE 30NM EYE THAT LINED
UP WELL WITH MICROWAVE EYE FEATURES IN THE 140534Z AMSR2 AND 140551Z ATMS
IMAGES. THE INITIAL INTENSITY OF 100KTS IS BASED ON MULTI-AGENCY DVORAK
CURRENT INTENSITY ESTIMATES OF T5.5/102KTS (PGTW AND RJTD), AND REFLECTS
THE SLOW WEAKENING TREND. UPPER LEVEL ANALYSIS INDICATES FAVORABLE
DYNAMICS WITH ROBUST DUAL OUTFLOW AND LOW (05-10KT) VERTICAL WIND SHEAR
(VWS); HOWEVER, THE SYSTEM HAS NOW DRIFTED INTO COOL SEA SURFACE
TEMPERATURES (26C) AND LOW OCEAN HEAT CONTENT (<10KJ/CM^2) THAT HAVE
BEGUN TO OFFSET THE FAVORABLE OUTFLOW AND VWS. THE CYCLONE CONTINUES TO
TRACK ALONG THE SOUTHERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE
(STR) TO THE NORTHEAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY VAMCO WILL TRACK MORE WEST-NORTHWESTWARD THROUGH THE REMAINDER
OF THE FORECAST PERIOD AS THE STR IS WEAKENED BY A MIDLATITUDE TROUGH TO
THE NORTH, MAKING LANDFALL OVER CENTRAL VIETNAM NORTHWEST OF HUE BY TAU
18. THE SYSTEM WILL CONTINUE TO WEAKEN DUE TO THE LOW SST AND OHC VALUES
IN THE SOUTH CHINA SEA APPROACHING VIETNAM, DOWN TO 90KTS BY TAU 12.
AFTER LANDFALL, THE RUGGED TERRAIN WILL RAPIDLY ERODE THE SYSTEM DOWN TO
65KTS BY TAU 24, 30KTS BY TAU 36, AND DISSIPATION BY TAU 48 AFTER IT
CROSSES INTO CENTRAL LAOS. NUMERICAL MODELS GRADUALLY AND EVENLY SPREAD
OUT TO OVER 250NM BY TAU 48, LENDING HIGH CONFIDENCE IN THE JTWC FORECAST
TRACK WHICH IS PLACED NEAR THE THE MULTI-MODEL CONSENSUS.//
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