The National Centre for Hydro-Meteorological Forecasting said the system would move northeast at about 10 kph before weakening into a low-pressure area and dissipating, posing no further direct threat to Vietnam.
Strong winds and rough seas were, however, expected to persist over the northern Gulf of Tonkin, the agency said.
The storm's circulation brought heavy to very heavy rain to northeastern Vietnam, while water levels on major northern rivers remained below warning level one and flooding on some mountain rivers had begun to recede.
From Sunday night to Monday, water levels on small rivers and the upper reaches of major rivers in northern Vietnam could rise by 2-4 metres, with some reaching warning levels one to two.
Forecasters warned of a high risk of flash floods and landslides in the northern mountainous and midland provinces of Lai Chau, Son La, Lao Cai and Quang Ninh.
The agency forecast 8-10 storms in the East Sea this year, fewer than the long-term average due to El Niño, with 3-5 expected to affect Vietnam, mainly between July and November.