South Australians have been told to brace for possible flooding – with up to two months’ rain expected – after already enduring a searing heatwave and catastrophic bushfire risk.

Major rain warnings are in place on Sunday, with a wet band stretching from eastern Victoria across southern SA, up towards the north-west.

Meteorologist Angus Hines said up to 100 millimetres of rain could fall over the eastern part of SA’s Eyre Peninsula – well above December averages of 15-30 millimetres

“The southern part of central SA becomes the focus point for quite heavy rain on Sunday – persistent falls, pretty much all day,” he said.

“For a lot of places, this weekend will represent two months of rainfall, if not more than that, for this time of year.

A severe weather warning was issued for SA’s Eyre Peninsula, west coast and north-west pastoral districts for heavy rain.

Victoria, Tasmania, the far south of NSW and parts of the Northern Territory can also expect high rainfall totals across the weekend.

The roof from a commercial building lands on a house in Wyong. Photo: Facebook (Fire and Rescue Wyong)

Savage storms

The wet change came after SA and NSW sweltered through a baking heatwave on Saturday, followed by night-time thunderstorms that smashed properties on the NSW central coast.

Roofs were ripped off homes when a strong southerly bluster swept up the NSW coast after 6pm, bringing a cool change after the mercury hit 44 degrees in parts of Sydney.

In Wyong, north of Sydney, the roof was lifted from a commercial building and landed on a home two properties away, trapping the occupant inside.

“The errant roof also brought down power lines, which further complicated the incident,” the Wyong Fire and Rescue Service said.

“The owner of the residence was inside the home at the time and he remained trapped, but uninjured and safe, until such time as the power could be isolated and a safe rescue undertaken.”

Emergency services also responded to incidents in Long Jetty and Toowoon Bay when a quick and powerful storm cell unleashed.

As well as multiple damaged homes, an entire shed was picked up and “only stopped due to a power pole”, according to an incident report on Facebook.

A shed whipped up by the storm wraps around a power pole. Photo: Facebook (NSW Central Coast Incidents)

States swelter

Residents were urged to check on vulnerable friends and neighbours on Saturday as much of NSW sweated it out under a dome of heat that had spread across the continent from the west in recent days.

Temperatures in Penrith and Richmond, in Sydney’s outer west, climbed to 43 degrees in the late afternoon, with Badgerys Creek reaching 44 degrees just after 4pm – the city’s highest temperature.

Sydney Airport broke its December record when the mercury hit 43.5 degrees about 1pm.

In Sydney’s west, 100,000 music fans sweated it out at Olympic Park concerts by the Foo Fighters and 50 cent and the EPIK indoor music festival, with the mercury climbing to 43 degrees.

The heat was widespread across the state, with the central and lower western districts also enduring extreme conditions and temperatures.

Forbes and Condobolin in NSW’s Central West both reached 44 degrees.

Heatwave warnings remain for all mainland states, with high to catastrophic fire danger alerts issued for sections of South Australia, northern Victoria, outback NSW and Greater Sydney.

Sydneysiders flock to Bondi Beach as the heat passes 40 degrees on Saturday. Photo: AAP

The cool change had already brought relief to southern states overnight, with Adelaide reaching a maximum 17 degrees and recording more than 20 millimetres of rain since 9am on Saturday.

About 35,000 households in South Australia lost power on Friday due to catastrophic bushfire risk, dry lightning and strong winds.

SA Power Networks said it had to disconnect about one-third of those customers due to fire risks, with all but 1400 reconnected to the grid by Saturday morning.

The NSW Rural Fire Service issued total fire bans for five state districts including Sydney, with several dozen fires burning but none out of control.

Cyclone Jasper on track

In Queensland, severe tropical cyclone Jasper has started to move towards the Australian coast and is tipped to make landfall in the middle of next week, bringing destructive winds and heavy rain.

As of Saturday afternoon, the category four system was in the Coral Sea about 970 kilometres east of Cairns and had started to swing towards northern Queensland.

Earlier in the day, a rescue helicopter safely evacuated four Bureau of Meteorology scientists from a remote weather station on Willis Island in the path of the wild weather, about 450 kilometres off Cairns.

The cyclone is tipped to weaken to a category two system on Monday but may then intensify again on Wednesday as it approaches the coast, the BOM’s Hines said.

He said it was likely to cross somewhere between Townsville and Cooktown but other scenarios were still possible, including a crossing further north.

“Wherever Jasper crosses it will be a significant weather event likely to bring damaging to destructive winds, heavy persistent rain that will lead to flooding, a storm surge along the coast and very dangerous conditions out over the water with large waves,” Hines said.

Queensland Police Acting Deputy Commissioner Shane Chelepy  warned households north of Mackay to prepare emergency kits.

The state disaster centre has moved to alert level, with local and district co-ordinators from Mackay to Cairns making preparations.

Queensland Fire and Emergency Services crews, including swift water rescue teams, are also primed to be deployed to cyclone-hit areas.

The system is the first tropical cyclone to form in Queensland waters in December in an El Nino year, which generally leads to fewer such weather events.

-with AAP