Average temperatures nationwide in August are forecast to be 0.5-1 degree Celsius above the long-term average, and even higher in some areas.
The south-central coast is expected to experience more hot days than usual, with severe and locally extreme heat possible.
Meanwhile, the number of hot days in northern Vietnam and areas from Thanh Hoa to Hue is expected to be lower than the long-term average.
Hot weather is forecast across much of the north, except Lai Chau and Dien Bien on August 11-12, as well as areas from Thanh Hoa to Danang and eastern parts of Quang Ngai and Gia Lai.
Daytime highs are expected to reach 35-37 degrees Celsius, exceeding 38 degrees in some places, with relative humidity falling to 55-60 per cent. The hottest period is expected between 11 am and 5 pm.
On August 10, temperatures at 1 pm reached 37.9 degrees Celsius at Lang station in Hanoi, 37.2 degrees in Bac Ninh and Nho Quan in Ninh Binh, and 37.1 degrees in Quang Ngai.
Forecasters warned that outdoor temperatures could feel one to three degrees higher than forecast, or more over concrete and asphalt surfaces.
The combination of high temperatures and low humidity could increase the risk of fires, while prolonged exposure to heat may cause dehydration and heat-related illness.
People are advised to limit outdoor activities during the hottest hours, stay hydrated and take particular care of children, the elderly and people with underlying health conditions.