Our native marsupials are sweltering through the severe heatwave conditions too.

Griffith resident Murray came across a possum in his shed on Monday afternoon looking heat stressed, as the temperature peaked at 36.1 degrees.

The possum was grateful for a big bowl of water and a peach to help cool down in the heat.

When Murray got home from work, he found the possum lying on its back in his shed before it scampered up under the hot tin roof.

"She is the regular thief of our peaches, so I know that's a favourite kind of dish," he said.

With hotter temperatures forecast for the rest of the week, it serves as a timely reminder that we also need to look after pets and native animals in the capital.

RSPCA ACT's Jacqueline Bunt said everyone needed to take good care of their pets in the heat, making sure they had plenty of water and shade through the day – and the occasional iced treat. And while it was best to keep pets indoors on days of extreme heat, making sure they could stay as cool as possible outside was the best option if pets had to be kept outside.

"We're still getting calls all the time regarding pets in hot cars. It only takes six minutes for an animal to die in a hot car," she said.

The RSPCA also recommended leaving water out for native animals away from where they might be attacked by predators in a bowl they can easily climb out of, Ms Bunt said.

North to northwesterly winds are still bringing warm air from central Australia into NSW and the ACT, which is driving higher than average temperatures, Bureau of Meteorology forecaster Anita Pyne said.

"It's hot, that's the story," she said.

By 11am on Tuesday, Canberra had already reached 34 degrees on a way to a forecast maximum of 39. Overnight, the temperature dropped to 19 degrees.

The city recorded the forecast maximum of 39 degrees at 1.30pm.

But a cool change is expected late on Friday or early Saturday morning, with southerly wind expected to bring cool air from the south.

First Canberrans will have to swelter through three days of 40 degrees or above.

"The last time we had four days in a row above 39 degrees was in January 2014. We had four days hovering between 39 and 40," Ms Pyne said.

"We could potentially get hotter than that."

The record for the hottest Canberra day on record, which was set on February 1, 1968 when temperatures reached 42.2, could also be broken this week.

"It's not out of the question but we're not currently forecasting that for Canberra at the moment," Ms Pyne said. "There's a chance."

The severe heatwave, which will become extreme by the end of the week, will see very warm overnight temperatures that won't drop below 20 degrees until Sunday.

The weather bureau defines a heatwave as three or more days with the day and night temperatures above average for a particular location, Ms Pyne said.