Spiral banding and other organizational features have increased around Tropical Depression 21W and it has intensified into Tropical Storm Sinlaku.  At 7:00 p.m. EST on Thursday the center of Tropical Storm Sinlaku was located at latitude 10.9°N and longitude 117.3°E which put it about 360 miles southwest of Manila, Philippines and about 650 miles east-southeast of Quy Nohn, Vietnam.  Sinlaku was moving toward the west-northwest at 23 m.p.h.  The maximum sustained wind speed was 40 m.p.h. and there were gusts to 50 m.p.h.

Sinlaku is being steered to the west-northwest by a subtropical ridge located to its north and that steering pattern is expected to continue for the next two or three days.  Sinlaku could be near the coast of Vietnam in about 42 hours.  The spirals bands of thunderstorms are increasing in organization and the upper level outflow is increasing.  Sinlaku will remain over warm Sea Surface Temperatures as it moves toward Vietnam.  The environmental factors suggest further intensification is likely, although the rapid forward motion of Sinlaku could limit the rate of intensification.  If Sinlaku were to move more slowly, then a faster rate of intensification night be possible.

Sinlaku is likely to bring some gusty winds to the coast of central Vietnam and it could produce locally heavy rainfall over parts of Southeast Asia as it moves inland in two or three days.