The heat arrives just as tens of thousands of rev heads pour into the city for the annual Summernats car festival.

Festival organisers said they were prepared with water and sunscreen to hand out to patrons. They have warned everyone attending to take it easy in the heat.

On Saturday, bureau forecasters are expecting a top of 36 degrees during the day.

And the hot day will likely turn into a warm night.

Bureau of Meteorology forecaster Stephen Stefanac said the bureau expected a minimum of 21 when the sun went down, which was "quite balmy for Canberra".

Sunday heats up to an expected 37 or 38 degrees around Canberra. Belconnen, set to reach 39 degrees, is the pick for the city's hottest suburb.

The weekend's temperatures will be the hottest days of the year so far in Canberra.

A shower or two is also expected around the region on Sunday.

Summernats co-owner Andy Lopez warned patrons about the hot weather.

"Our advice, Take it easy, drink water, moderate alcohol consumption. We do have free water around the site available to patrons," Mr Lopez said.

He said there would be crews to offer water and sunscreen to those who may be queuing for tickets.

Festival staff would also be working hard to get people through the gates quickly, he said.

"We have fantastic first aid and medical should anyone get affected by the heat. Our RSA policies for service of alcohol are second to none.

"It is going to be hot, we encourage people to take it easy, take care of yourselves, take care of your mates and if you need it, we will be here to take care you of as well."

People were also expected to descend on the city's pools.

A senior staff member at Dickson aquatic centre said they were expecting a huge crowd of families and kids over the weekend as a result of the hot weather. She said extra lifeguards would be on duty.

ACT Rural Fire & Rescue has updated its fire danger forecast rating for the weekend to very high.

Bureau forecaster Mr Stefanac said the heat was caused by a high pressure system over the Tasman Sea drawing hot air from northern Australia.

The air was drawing southwards across south eastern Australia and affecting Canberra, the forecaster said.

Moving across to the coast, Mr Stefanac said the prediction for Batemans Bay was for cooler temperatures.

Saturday has a top of 32 degrees and mostly sunny.

Sunday was expected to be partly cloudy and reach a top of 33.

"On Sunday a change comes pretty early in the day, and it doesn't have a chance to reach the hotter temperatures," Mr Stefanac said.

The rest of the week in Canberra looks warm with a few showers into Thursday.