Sydney, Melbourne, Brisbane weather: Warnings issued for major cities

A massive heatwave, record temperatures, a possible cyclone and dangerous storms are all set to hit Australia in the next few days. 

Almost every state and territory is forecast to suffer a low-intensity to severe heatwave this weekend while storms hit the country's southeast. 

Meanwhile, Queenslanders have been told to prepare for a category five cyclone to make landfall.

Sydney

Sydney is expected to see its hottest day in almost four years as much of New South Wales swelters through a severe heatwave.

The city's low-lying western suburbs, Penrith and Richmond, are almost always the hottest places to be in Sydney and that will again be the case on Saturday.

Temperatures in the west are forecast to reach 42C, temperatures similar to the Black Summer bushfire season in 2019/2020.

Weatherzone meteorologist Anthony Sharwood explained the sea breeze in eastern suburbs makes it difficult to predict how hot the city will get.

'At this stage, the city is forecast to reach 38C, however it could top 40C depending how things play out,' he said.

'It's notoriously difficult to forecast Sydney's maximum temperature when you have an arm wrestle between the hot northwesterly stream and the cooling sea breeze. 

'Even an hour or two of delayed sea breezes can mean several extra degrees of afternoon warming.

'Whatever happens on Saturday, you can bet the pools and beaches will be crowded right across Sydney.'

Fortunately, a strong southerly wind change is expected to bring temperatures down by 10C in the mid-evening on Saturday. 

During last year's La Niña, Sydney city did not crack 30C during December. The hottest temperature was 29.7C on Christmas Eve.

Partially cloudy skies over Sydney are expected to stay the same through to Sunday when showers develop.

The lead-up to Saturday's heat is also looking warm with a top of 28C on Thursday and 31C on Friday. 

Meanwhile, almost the entire state of NSW is forecast to suffer through a severe heatwave through to the end of the week.

A low-intensity to severe heatwave will affect NSW and the ACT as well as parts of southern Queensland and the Cape York Peninsula, northeast South Australia and parts of northern Western Australia.

Isolated pockets along NSW's South Coast could experience extreme heatwave conditions. 

A low-intensity heatwave will affect areas of the Northern Territory, western parts of Queensland and far northeast Victoria.

NSW Health urged residents to plan ahead and take steps to beat the heat as high temperatures linger during the next few days.

Heatwaves can particularly affect people aged over 65, babies, young children, pregnant women and the homeless.

Hot weather could put a strain on the body by exacerbating underlying health conditions, NSW Health executive director Jeremy McAnulty said.

'It is important for people to know the symptoms of heat-related illnesses and take precautions to keep themselves and their loved ones cool,' he said.

'If they can, they should also take the time to check on vulnerable and elderly neighbours and family to ensure their safety in the heat.'

Brisbane

Brisbane is also set for a hot end to the week with top temperatures cracking the low 30Cs through to next week.

Sunny skies over the city on Thursday are expected to grow cloudy on Friday and stay that way through the weekend.

Meanwhile, central and north Queenslanders have been warned to brace for a possible cyclone.

Cyclone Jasper formed over the Solomon Sea late Tuesday afternoon. 

While it is still too early to know if the system could reach Australians shores or where it will fall, it is likely Cyclone Jasper will move southwest towards Queensland and gain strength in the coming days. 

'The Bureau of Meteorology expects Jasper to become a category three severe tropical cyclone tonight and possibly reach category four strength on Friday,' Weatherzone meteorologist Ben Domensino said.

'Unfortunately, forecast models are not agreeing on when this steering ridge will break down, which makes it difficult to know where Jasper will move as it tracks closer to Australia early next week.'

On Thursday morning, the Bureau predicted Cyclone Jasper would become a category five system on Thursday night. 

'Jasper is forecast to gradually move in a general southwesterly track towards the Queensland coast early next week,' it said.

'At this stage the highest risk of a cyclone impact is the region north of Mackay but the timing and severity of the coastal impact remains highly uncertain at this stage.'

However, other forecast models show the cyclone could reach down to Gladstone.

Anyone in central and north Queensland has been urged to regularly monitor cyclone advisories for updates. 

Adelaide

South Australia's early summer heatwave is set to descend into chaos this weekend with possibly dangerous thunderstorms forecast over Adelaide.

Northern SA has bared the brunt of the state's heatwave with maximum temperatures cracking 46C earlier this week.

Those high temperatures are set to continue on Thursday and Friday with highs of 33C and 36C respectively forecast in Adelaide.

However, cloudy weather and a possible storm on Friday will drastically change to dangerous conditions and temperatures in the low 20Cs from Saturday.

'During the coming weekend and into the new week, an upper-level cut-off low looks likely to stall over South Australia, causing a mix of dangerous weather – possibly including heavy rain, severe thunderstorms and damaging winds,' Mr Sharwood forecast.

'The model below predicts the accumulated 7-day rainfall from this Wednesday to next Tuesday inclusive. 

'It goes without saying that you don't expect to see zones of purple or blue, representing 100 mm to 200 mm of rainfall, in South Australia during summer.'

The massive system combined with damaging winds is expected to cause widespread power outages in Adelaide on Sunday. 

Showers are expected to follow the storms over Adelaide through to late next week.

Melbourne and Hobart

A complex series of troughs and a cold front is forecast to drive storms across southeast Australia this weekend, including Melbourne and Hobart.

'Tomorrow we will see a trough and cold front moving over the southeast bringing showers, storms and heavy rainfall as well as damaging winds to Adelaide, Melbourne and Hobart,' Weatherzone meteorologist Yoska Hernández said.

'On Friday, Adelaide, Melbourne and northern Tasmania will see thunderstorms while Hobart will get heavy rain.

'There will also be potentially damaging winds gusts over parts of South Australia and potentially Melbourne where winds could reach between 80 to 90km/h in elevated areas and the ranges.

'For Melbourne, the heaviest rain will be on Saturday with 20 to 30mm falling.

'Hobart will see its heaviest rain on Friday with totals between 15 to 20mm.'

Canberra

Australia's capital is also expected to see rain from the trough-cold front system on Thursday and Friday before the skies partially clear on Saturday.

However, Ms Hernández warned winds could reach between 70 and 90km/h in the city on Saturday.

Perth

Winds could reach up to 45km/h in Perth at midday Thursday before tending southeast to southwesterly in the evening.

Temperatures are forecast to slowly pick up as the city heads into next week with a top of 27C on Thursday, 28C on Friday, 30C on Saturday and 32C on Sunday. 

Darwin 

Darwin's wet season is still in full swing with storms forecast through to next week coupled with high temperatures in the low 30Cs.