The Bureau of Meteorology is forecasting a severe heatwave for Canberra for Friday, Saturday and Sunday, when temperatures are expected to make to the high 30s.

The bureau defines a heatwave as "three days or more of high maximum and minimum temperatures that is unusual for that location".

"Severe heatwave conditions can be expected over southern NSW [including the ACT], the northern parts of Victoria and Tasmania, near the Victorian, NSW and South Australian border and also near the northern border of South Australian and Western Australia, extending slightly into the southern interior district of WA," it said.

There was also a "very small area of extreme heatwave conditions are forecast in the far southeast of NSW", just to the south-east of the ACT.

On Friday, the nation's capital is forecast to reach a maximum of 38 degrees with temperatures staying around that mark for the rest of weekend with very little chance of rain to ease the pain.

Weatherzone meteorologist Graeme Brittain said the string of high 30 degree days was above the January average.

Saturday is expected to be the hottest day over the weekend, and the heat is tipped to be about 8 to 10 degrees above the month's average.

Overnight temperatures are also on the rise. Saturday and Sunday mornings are expected to only drop to 16 and 17 degrees and Monday a warm 20 degrees. This would be above the January average by 4 to 5 degrees.

According to Weatherzone, the UV index will also be at an extreme level over the weekend. Authorities are asking people to make sure to stay hydrated and wear sunscreen and a hat if in the sun.

ACT Health recommends people remain hydrated during the extreme heat. They urge people to avoid alcohol or caffeine, particularly if dehydration is suspected, stay out of direct sunlight and avoid strenuous activity in the heat of the day.

Infants and children, pregnant women, the elderly and people with pre-existing medical conditions are at greater risk of heat related illness.

Places to escape the heat in Canberra this summer: