From August 1-2, scattered showers and thunderstorms are forecast across northern Vietnam, Thanh Hoa and Nghe An, with isolated heavy rain, according to the National Centre for Hydro-Meteorological Forecasting.
Rainfall is expected to intensify from the evening of August 2, with some areas likely to experience heavy to very heavy downpours.
Scattered showers are also forecast for areas from Ha Tinh to Danang and eastern Quang Ngai, while the Central Highlands and southern Vietnam are expected to see afternoon and evening thunderstorms, some of them heavy.
Forecasters warned that thunderstorms could bring lightning, hail and strong winds.
As of 8 pm Friday, Super Typhoon Dolphin was located about 2,730 km southeast of Tokyo, packing maximum sustained winds of 216 kph, according to China's National Meteorological Centre.
The storm was moving west-northwest at 20-25 kph and is expected to maintain its current intensity in the near term.
Japan Meteorological Agency classified Dolphin as a violent typhoon, the highest category in its warning system.