Tropical Storm Haikui weakened as it moved southeast of Hainan Island on Saturday. At 10:00 p.m. EST on Saturday the center of Tropical Storm Haikui was located at latitude 17.6°N and longitude 112.6°E which put it about 290 miles (470 km) east of Da Nang, Vietnam. Haikui was moving toward the west-southwest at 6 m.p.h. (10 km/h). The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h). The minimum surface pressure was 999 mb.
A combination of drier air and strong vertical wind shear weakened Tropical Storm Haikui on Saturday. Strong northeasterly winds transported colder drier air from eastern Asia into the circulation of Tropical Storm Haikui. The drier air reached the core of the circulation and it prevented the formation of new thunderstorms around the center of circulation. Strong westerly winds in the upper levels were blowing over the top of the circulation. The combination of northeasterly winds in the lower levels and westerly winds in the upper levels produced strong vertical wind shear. The wind shear blew the upper portion of the circulation to the east of the low level core of Tropical Storm Haikui. The core of Tropical Storm Haikui consists of a circular rotation of showers and low clouds. The only thunderstorms are occurring in a rainband on the northeastern periphery of the circulation.
The strong wind vertical wind shear and drier air should continue to weaken Tropical Storm Haikui. Haikui is likely to weaken to a tropical depression on Sunday. Since the circulation exists primarily in the lower levels, it will be steered by the winds closer to the surface of the Earth. The northeasterly winds in the lower levels will steer Tropical Storm Haikui toward the west- southwest. On its anticipated track Tropical Storm Haikui will pass south of Hainan Island. Haikui or its remnants could reach the coast of Vietnam in 36 to 48 hours.