As much of southeast Australia breathes a sigh of relief after a short but intense heatwave, parts of NSW brace for the mercury to hit 40C.

Extreme heat is predicted for parts of western Sydney on Tuesday, with the harbour city expecting a top of 33C while Penrith and Richmond are forecast to reach 42C.

Temperatures pushed into the mid-40s in parts of NSW, Victoria, SA and Queensland on Monday in one of the hottest December days since 2019.

A slight reprieve is expected for NSW on Wednesday with cooler conditions and showers expected before returning to warmer conditions on Sunday.

Despite a cold front easing conditions in southeast Australia overnight, total fire bans remain in northwest Victoria and heatwave conditions are expected to linger for days in the NT and southern Queensland.

Extreme conditions persist in Victoria’s Wimmera Fire District after firefighters battled more than 40 grass and scrub fires in Cresswick near Ballarat, State Control Centre spokesman Luke Hegarty said.

Residents near the 200ha bushfire in Cresswick were told to evacuate overnight but the situation had improved enough for the warning level to be downgraded to advice.

A 10-year-old boy died in Mooroopna in the state’s north on Sunday with reports he died after playing in a car boot as temperatures reached 35C.

Brisbane, Mackay and Townsville could face heavy rain and flash flooding, with isolated downpours of up to 250mm forecast.

Insurers urge Australians to prepare for the season ahead, with NRMA research noting 42 per cent of wild weather claims it receives arrive in summer, retail claims executive general manager Luke Gallagher said.

The data showed more than one in 10 Australians had returned from holidays to find their homes damaged by thunderstorms, hail, floods, wild winds or bushfire.

While this week’s heatwave was relatively short-lived for much of the nation’s southeast, these events are expected to become hotter, longer and more frequent, according to Monash University associate professor Ailie Gallant.

“These are some really hot temperatures for mid-December that we haven’t had in quite a few years,” Dr Gallant told AAP, noting the increased fire risk.

This post was originally published on Michael West.