A motorbike driver is covered up on a Hanoi street. Photo by VnExpress/Quy Doan
The capital is set to be exposed to an UV index of 11 from Friday to Sunday, World Weather Online says.
AccuWeather forecasts that the maxium UV index in the city will reach 13 on Friday and Saturday, and 12 on Sunday, saying it will be "very hot."
The UV index is an international standard measurement of the strength of ultraviolet radiation from the sun. Between 0 and 3 is considered low and above 11 is deemed extreme with radiation that could burn skin and damage eyes within 20-30 minutes.
The capital city is also likely to experience maximum temperatures consistently above 40 degrees Celsius (104 degrees Fahrenheit), reaching as high as 46 degrees until next week, according to weather forecasts.
High UV levels can accelerate skin aging and pose more severe threats like skin cancer, said Trinh Ngo Binh, a dermatologist based in Saigon.
He advised people to avoid direct exposure to sunlight between 10 a.m. and 3 p.m. and to wear sunscreens, sunglasses and brimmed hats if they have to go out under the sun.
Hanoi is experiencing a heat wave until the end of this week because of a developing low-pressure area from the west, according to the National Hydro-Meteorological Forecasting Center.
The capital city and other northern provinces could experience temperatures as high as 38 degrees Celsius within the period, the center said.
Last month, Vietnam broke its national high temperature record as the mercury hit 43.4 degrees Celsius in the north central Ha Tinh Province, according to a forecaster at the French meteorological agency Meteo France.
Weather experts have warned that Vietnam should brace for more heat waves set to sweep through the country this summer.
A study published in the journal Climatic Change last September said that Southeast Asian nations like the Philippines and Vietnam would be most affected by heat-related mortality, along with countries in Southern Europe and South America.