The mercury will be even higher in northern and central parts of central Vietnam, averaging at 37-40C, with readings in some places expected to hit 41-42C.
The lowest relative humidity will be in the range of 30-50% while the number of hours per day with temperatures of 35C or above will range from 10-18 hours.
In the capital of Hanoi, the maximum temperature on June 22 will reach 39C, or even higher in some locations, while the UV index is measured at 8-9, meaning a very high risk with direct exposure to the sun.
The provinces from Thanh Hoa to Thua Thien Hue are expected to see the highest temperatures at 40C and above.
The weather agency has warned of a high risk of explosions and fires in residential areas due to increased power demand as well as a risk of forest fires in north and central-central regions.
It has also warned of heatstroke and dehydration as a result of prolonged exposure to high temperatures.