The National Centre for Hydro-Meteorological Forecasting said the system, which weakened from Storm Saudel, moved into the northern East Sea early on August 31 and strengthened again into a tropical depression.
It is forecast to move slowly east-southeast before potentially developing into a storm. If it does, it will become the fifth storm to enter the East Sea this year.
During September 1, the storm is forecast to turn east-northeast and move at about 20 km/h, with little change in intensity.
By the morning of September 2, its centre is expected to be over waters northeast of the northern East Sea, with winds at level 8 and gusts at level 10, before gradually weakening into a tropical depression.
The northwestern part of the northern East Sea is forecast to see winds at levels 6-7, gusting to levels 8-9, and waves of 2-4 metres. Near the storm's centre, winds could reach level 8, gusting to level 10, with waves of 3-5 metres and rough seas.
Vessels in affected waters were warned of thunderstorms, tornadoes, strong winds and high waves.
The tropical convergence zone linked to the depression is also forecast to bring heavy rain to parts of central and southern Vietnam.
Thanh Hoa and areas as far south as northern Quang Tri are forecast to receive 30-60 mm of rain on August 31, with isolated totals exceeding 130 mm.
From the evening of August 31 through September 1, areas from southern Quang Tri to northern Danang could receive 40-70 mm, with isolated totals above 150 mm.
The Central Highlands and southern Vietnam are forecast to see 15-30 mm of rain on the afternoon and night of August 31, with isolated totals exceeding 70 mm. Thunderstorms could bring tornadoes, lightning and strong wind gusts.
