The Southern Regional Hydrometeorological Centre forecast scattered showers and thunderstorms across HCM City and southern provinces on October 18, with rain becoming more widespread in the afternoon and evening.
Some areas could experience heavy rainfall, while temperatures are expected to range from 23-26 degrees Celsius overnight to 31-34 degrees during the day.
Meteorologists said upper-level easterly disturbances were intensifying, bringing unstable weather systems inland from the sea and increasing the likelihood of rain across southern Vietnam.
Rainfall is forecast to increase in both intensity and coverage over the next few days, with heavy downpours possible in some locations.
At sea, a strengthening low-pressure trough stretching along 5-8 degrees north latitude is expected to bring deteriorating conditions, including thunderstorms, possible waterspouts and gusts reaching force 7-8 on the Beaufort scale.
Coastal waters from Lam Dong to Ca Mau are forecast to experience northeasterly to easterly winds of force 3-4, rising to force 4-5 off Lam Dong.
Waves are expected to reach 0.5-2 metres, potentially exceeding two metres during thunderstorms, with occasionally choppy seas.
Meanwhile, waters from Ca Mau to An Giang are forecast to have light winds and waves of 0.5-1.5 metres, although wave heights could exceed 1.5 metres during thunderstorms.
Weather authorities advised residents to monitor forecasts and take precautions against heavy rain, lightning, strong winds and possible tornadoes.
Fishing boats and other vessels were urged to exercise caution during thunderstorms and seek safe shelter if conditions deteriorate.