Cyclone Alfred: What we know about rare storm nearing Australian coast

Residents are being told to brace themselves for the "significant risks" Cyclone Alfred poses. The cyclone will be the first to hit Southeast Queensland and northern New South Wales for 51 years.

But what is a cyclone, what kind of threat does it pose, and what is being done about it?

What is a cyclone?

A tropical cyclone is a rapidly rotating storm that begins over tropical oceans. It can vary in speed, size, and intensity.

The term cyclone is used once a storm reaches maximum sustained winds of 74mph or higher.

A cyclone is the same phenomenon as a typhoon or hurricane, but they are referred to differently depending on where they happen.

The term cyclone is used when the storms occur in the South Pacific and Indian Ocean. They are referred to as typhoons when they appear in the Northwest Pacific and as a hurricane in the North Atlantic, central North Pacific and eastern North Pacific.

What kind of threat does Cyclone Alfred pose?

Alfred was 150 miles east of Brisbane and moving west on Thursday, with sustained winds near the centre of 59mph and gusts of 81mph, according to meteorologists.

It is forecast to cross the Queensland state coast early on Saturday, somewhere between the Sunshine Coast region and the city of Gold Coast to the south.

The storm is expected to maintain its wind strength before hitting land and "continue to develop", according to Australia's Bureau of Meteorology.

But the forecast rainfall is expected to be the biggest threat, with a risk of life-threatening flooding.

Total rainfall could be as much as 80cm in some regions - more than the average total for March, the bureau said.

"Large swells and powerful waves have been observed along the Queensland coast for several days now with severe coastal erosion and inundation happening," the bureau's manager Matt Collopy said.

"This will continue and likely get worse as the system approaches and makes landfall.

"The wave, wind, rainfall and particularly the storm surge present significant risks."

Modelling shows up to 20,000 homes in Brisbane, a city largely built on a river floodplain, could experience some level of flooding.

Australian meteorologist Tony Auden told Sky News the cyclone is likely to be on a scale the country hasn't seen in a "generation" or "a lifetime".

He said the last comparable cyclone to hit the area was in 1954.

"The worry here is back then, the population in the firing line was 36,000 people - this time, it's 4.5 million people in that firing line, with some very nasty weather on the way in the next few days," Mr Auden explained.

What is happening now?

The millions of residents in the cyclone's path gained an extra 24 hours to batten down as meteorologists revised their prediction of the cyclone making land late Thursday or early Friday to early Saturday.

But early wind and rain from the storm started lashing part of eastern Australia on Thursday and strong winds downed trees and cut power to 4,500 homes and businesses in northern New South Wales, officials said.

Rivers were rising across the region due to the heavy rain, and emergency authorities advised 14 communities in the state's north to evacuate their homes on Thursday to avoid the risk of being trapped by floodwaters.

The coast near the border has already been battered for days by abnormally high tides and seas. A 40ft wave recorded off a popular Gold Coast beach on Wednesday night was a record for the area, officials said.

Brisbane streets are largely empty of traffic and supermarket shelves have been stripped bare of basics including bread, milk, bottled water and batteries.

What is being done about it?

Cyclone Alfred weather warnings cover more than 500km (311 miles) across the coast in the states of Queensland and New South Wales, impacting millions of people.

More than 1,000 schools in southeast Queensland and 250 in northern New South Wales were closed on Thursday, while public transport across Brisbane has been suspended.

Many of the areas likely to be badly affected have already been evacuated, after authorities urged residents to clear the regions by Thursday morning if possible.

A number of flights in the affected regions have been cancelled, and operators have warned more are likely over the coming days.

Hospitals are not carrying out non-urgent surgeries and public transport is not running until the danger passes, Brisbane officials have said.

Australian Prime Minister Anthony Albanese stressed the importance of preparatory work ahead of the cyclone's arrival.

He said on Wednesday that heavy-lift helicopters had been deployed and offered to "provide whatever resources are required" for the state governments.

The federal government said it had provided Brisbane with 310,000 sandbags with more on the way, and some residents have been seen stacking them to protect low-lying properties.

However, there were reports on Thursday of sandbag shortages in the city leading desperate homeowners to buy sacks of potting mix as an alternative.

Sports events have also been called off - most notably the Australian WPGA Championship and two Australian Football League matches in Queensland.

Queensland Premier David Crisafulli said: "This is a very rare event for southeast Queensland, I acknowledge that, but I'm asking Queenslanders to take it seriously and I want you to know that we are taking it seriously.

"If you are in a storm tide zone or you're in an area where you know there is riverine flooding, you really need to consider and think about your evacuation plan now," he added.

On Monday, an adventurer had to be rescued by a warship in the Coral Sea around 460 miles east of the Queensland coast after getting caught up in the cyclone's 50mph winds.

Lithuanian rower Aurimas Mockus, 44, was in the final stages of his 7,500-mile voyage across the Pacific Ocean from the US to Australia, which he started in an enclosed boat in October, when he became stranded for three days before being rescued.

A brief history of cyclones

Cyclones are common in Queensland's tropical north but are rare in the state's temperate and densely populated southeast corner that borders New South Wales state.

The last cyclone to hit Southeast Queensland and northern New South Wales was Cyclone Zoe in March 1974.

It crossed the coast at the southern end of the Gold Coast on the New South Wales border and caused extensive flooding.

The last time a cyclone threatened Brisbane was in 1990, but the system tracked south just before reaching the city.

More than 1,900 disasters have been attributed to tropical cyclones worldwide since 1970, according to the World Meteorological Organisation, resulting in more than 790,000 deaths and $1.4trn-worth of damages.

-SKY NEWS