Tropical Storm Nangka formed over the South China Sea on Monday.  At 11:00 a.m. EDT on Monday the center of Tropical Storm Nangka was located at latitude 18.3°N and longitude 113.8°E which put it about 200 miles (325 km) east of Hainan Island.  Nangka was moving toward the west at 17 m.p.h. (28 km/h).  The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 996 mb.

More thunderstorms developed near the center of a low pressure system over the South China Sea on Monday and the Japan Meteorological Agency designated the system as Tropical Storm Nangka.  The circulation around Tropical Storm Nangka exhibited more organization on Monday.  More thunderstorms formed near the center of Nangka.  Bands of showers and thunderstorms were revolving around the center of circulation.  Storms near the center generated upper level divergence which pumped mass away to the west of the tropical storm.  Winds to tropical storm force extended out 75 miles (120 km) from the center.

Tropical Storm Nangka will move through an environment favorable for intensification during the next 12 to 18 hours.  Nangka will move over water where the Sea Surface Temperature is near 30°C.  It will move south of an upper level ridge over eastern Asia.  The ridge will produce easterly winds which will blow toward the top of Tropical Storm Nangka.  Those winds will cause moderate vertical which shear.  The shear will slow the rate of intensification, but it will not be strong enough to keep Nangka from intensifying.  Tropical Storm Nangka will weaken in a day or so while the tropical storm moves over Hainan Island.  Nangka could restrengthen when it moves west of Hainan.

Tropical Storm Nangka will move south of a high pressure system over eastern Asia.  The high will steer Nangka toward the west-northwest.  On its anticipated track Tropical Storm Nangka will reach Hainan Island in less than 18 hours.  Nangka will bring gusty winds and locally heavy rain to Hainan.  Flash floods could occur in some locations.  Tropical Storm Nangka will reach northern Vietnam in two days.

Elsewhere over the Western North Pacific Ocean, Tropical Depression Chan-hom was weakening southeast of Japan.  At 5:00 a.m. EDT on Monday the center of Tropical Depression Chan-hom was located at latitude 29.2°N and longitude 142.5°E which put it about 400 miles (645 km) south-southeast of Tokyp, Japan.  Chan-hom was moving toward the south at 9 m.p.h (15 km/h).  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind guts to 45 m.p.h. (75 km/h).  The minimum surface pressure was 1000 mb.