Sinlaku evolved from a tropical depression Saturday, the National Center for Hydro-Meteorological Forecasting said.

As of 4 p.m., the storm's eye was over mainland China's Hainan Island and about 330 km off the coast of Thai Binh Province of northern Vietnam and north-central Nghe An Province to the southeast. Its maximum wind speed near the eye recorded at 75 kph.

In the next 12 hours, the storm would move west-northwest at about 15-20 kph, entering the Gulf of Tonkin. By 4 a.m. Sunday, the storm's eye would cover sea regions from Thai Binh to Nghe An, with a maximum wind speed of 75 kph.

The storm would continue to move west-northwest at about 15 kph and make landfall in north-central and northern Vietnam, before devolving into a tropical depression. By 4 p.m. Sunday, the tropical depression would have a maximum wind speed of about 50 kph.

The Hong Kong Observatory also anticipated the storm would move west-northwest before making landfall in northern Ninh Binh to north-central Ha Tinh provinces Sunday afternoon. By 3 p.m. the same day, the storm would devolve into a tropical depression with a maximum wind speed of 55 km/h, according to the Observatory.

Due to the storm's impact, several parts of the South China Sea, including regions near Vietnam's coast, should expect strong winds and rough seas. From Saturday to Sunday, heavy rains of up to 500 mm each time should be expected in areas from north-central Thanh Hoa to Quang Tri provinces. Besides, northern Vietnam should expect downpours with rainfall up to 400 mm each from Saturday to Wednesday. Rainfall of 180 mm a day is considered heavy.

Hanoi should expect rainfall between 150-250 mm each downpour from Saturday to Monday, with more rains to be expected until Wednesday.

Nghe An authorities have recalled over 3,000 vessels carrying over 15,000 sailors to shore in response to the incoming storm. As of noon Saturday, over 400 vessels with about 1,600 on board are still operating off of the Nghe An coast, though all have been notified of the storm's trajectory to seek shelter.

Hundreds of other vessels operating near Ha Tinh and Quang Tri have also been notified of the incoming storm, which is the second storm to appear on the South China Sea this year.

The first storm, Nuri, came in mid-June. While it never made landfall in Vietnam, it caused strong winds and heavy rains in several areas, including HCMC. At least one motorbike rider in the city was killed by a falling tree branch during a downpour on June 13.

The South China Sea, which Vietnam calls the East Sea, could see 11-13 storms and tropical depressions this year, half of them directly affecting the country, meteorologists said.