A unique weather pattern involving a tropical cyclone, heatwave and two ‘omega blocks’ is expected to have a severe impact across Australia from this weekend that could affect every state.

Tropical Cyclone Jasper formed 1500 kilometres north-east of Cairns on Tuesday afternoon, becoming the first cyclone off Queensland in December during an El Nino year.

It’s expected to intensify into a severe tropical cyclone by Thursday as it moves south-south-west through the Coral Sea. But there is “large uncertainty” as to which parts of the coast will be affected.

Australians have also been warned to brace for a heatwave that could affect part of every mainland state and territory, with temperatures in western Sydney expected to reach the low-40s on Saturday.

Weatherzone said a weather pattern known as an “omega block” – which drove record-breaking heat in Europe in June 2022 and Canada in June 2021 – was behind the scorching outlook.

Not one, but two, omega blocks are expected to form, along with Cyclone Jasper, creating a “dynamic mix of severe weather”.

Weatherzone said an omega block is a broad-scale weather pattern that involves an area of high pressure being straddled by two adjacent areas of low pressure.

“These weather patterns cause the isobars on a northern hemisphere synoptic chart to form a shape similar to the Greek letter omega Ω, hence the name omega block,” it said.

“Omega blocks tend to cause severe weather because they slow or block the passage of weather systems that are trying to move from west to east across Earth’s surface.”

A forecast image of twin omega blocks near Australia on Sunday evening. Photo: Weatherzone

Weatherzone said forecast models predicted two omega blocks will form near Australia and across the South Pacific Ocean later this week.

“This blocking pattern will cause an upper-level high to linger over eastern Australia through the second half of this week and into next week,” it said.

“The position of this stubborn high pressure system will allow a few things to happen in the Australian region:

• A hot air mass will spread across Australia on the western side of the upper-level high, causing a prolonged and intense heatwave over a large area of the country;
• The northern flank of the high will straddle a tropical cyclone over the Coral Sea and likely direct it towards eastern Queensland early next week;
• The stubborn high may also cause an upper-level cut-off low to pass over South Australia this weekend or early next week. This low is likely to cause a mix of dangerous weather, possibly including heavy rain, severe thunderstorms and damaging winds.

“This weather pattern could produce severe weather in multiple states concurrently, so be sure to stay up to date with the latest forecasts, warnings and tropical cyclone advisories,” Weatherzone said.

Tropical Cyclone Jasper

The cyclone is a slow-moving category one weather system about 1500 kilometres north-east of Cairns.

It’s expected to strengthen and become a severe category three tropical cyclone on Wednesday as it tracks south-south-west towards the north-east Coral Sea.

“There is a potential for tropical cyclone Jasper to move near the Queensland coast next week [(but] there is large uncertainty as to which parts of the Queensland coast will be impacted,” weather bureau senior meteorologist Dean Narramore said on Tuesday.

“The bureau will issue regular updates to keep communities informed as the situation evolves over the coming days.”

Tweet from @BOM_Qld

Meteorologist Steven Hadley said some modelling suggested Jasper could travel south and cross the coast near Brisbane as a tropical low.

“But more likely than not, it would be in the tropical areas of Queensland … it’s just really too early to say just yet,” he told ABC radio.

The Bureau of Meteorology’s technical bulletin said recent models leaned towards Jasper approaching the Queensland coast between Cooktown and Mackay next week.

“A small amount of guidance has a more southerly track, consequently moving the system towards the Queensland coast, south of Mackay,” it said.

Vast heatwave

Meanwhile Australians are being warned to prepare for a heatwave that is expected to grip many parts of the country for days.

Much of NSW and parts of Queensland, SA, Western Australia, the Northern Territory and ACT are predicted to cop soaring temperatures until Friday.

NSW residents are in for a sweltering period with a severe heatwave warning issued from Wednesday. It is expected to last for three days.

The BOM has warned residents in NSW’s northern tablelands, central west slopes and plains and lower and upper western districts of above average maximum temperatures, with some areas tipped to reach the high 30s to low 40s.

There is also a severe heatwave warning for the Illawarra, Hunter and Riverina regions.

No total fire bans were declared but the NSW Rural Fire Service urged people in bushfire prone areas to have action plans ready in the case of an emergency.

NSW Health also warned about the effects of heatwaves on vulnerable people, including those aged over 65, babies, young children, pregnant women and the homeless.

People are being urged to avoid being outdoors during the hottest part of the day, to wear sunscreen, sunglasses and hats and stay hydrated.

NSW Police reminded commuters to keep their cool on the roads, particularly if there are traffic delays.

“We know many people will want to head to the beach, a local swimming hole or swim in your backyard pool, please be careful,” a NSW Police spokesperson said.

“Keep a watchful eye over children especially when they are near the water, all children need to be supervised.”

-with AAP