Australia Weather News

Tropical Cyclone Narelle has re-intensified over the Indian Ocean and is threatening to put Western Australia next on its hit list. 

The question is when, and where it will make its crossing — and could it make a rare crossing as far south as Perth?

The destructive system has already made a mammoth — and somewhat unusual — journey across the top of Australia, hitting both Queensland and the Northern Territory.

A WA crossing would make it the first cyclone in more than 20 years to make three separate landfalls across the two states and a territory.

Here's what we know about how it's managed to sustain the strength to make such a long trek across Australia.

Cyclone Narelle's path now

Cyclone Narelle is currently sitting off WA's Kimberley coast.

After briefly dropping below cyclone strength, it re-intensified overnight into a category one, thanks to the energy supply from warm oceans in the north.

Forecasts show it escalating into a category four cyclone over the next two days as it begins to curve around the Pilbara coast.

It will be over water when this happens, but Bureau of Meteorology (BOM) senior forecaster Angus Hines said it would still be close enough to the mainland to cause gales with damaging-to-destructive winds and large waves.

The BOM's warning zone currently covers an area of the coast from Cape Leveque to Mardie, with regions further south under a cyclone watch.

Could Cyclone Narelle cross near Perth?

On Friday, Narelle is likely to make a southwards turn towards Exmouth but beyond then its movements become less clear.

Mr Hines said the BOM was "very confident" it would curve again toward WA's west coast, most likely crossing over the weekend.

But how quickly that curve happens is where things get murky. This ultimately affects where it crosses, when it crosses and what strength it will be.

One of the outside possibilities includes a rare crossing as far south as Perth. But the most likely crossing point at the moment is around the western Gascoyne.

"So if that curvature happens really quickly, then it's likely to reach the WA coastline somewhere … around the Gascoyne coast, perhaps around Carnarvon or Shark Bay," he said.

"If that curve happens a little bit slower, then it will gradually drift a bit more southwards, [with] an impact somewhere around Geraldton in the central west, or around Kalbarri.

"And then there's even a chance that it happens even slower than that, we [could] see that tropical cyclone reaching the coast somewhere near Perth."

He said the crossing point should be clearer by Thursday or Friday.

Rain, regardless of Narelle's re-entry

Mr Hines said, regardless of its path, Narelle would come with its usual companion; plenty of rain for the state's south west.

"The rainfall and the potential for flooding is likely to permeate western and south-western WA in any situation," he said.

The wind strengths are most in question. 

"As we know, the wind impacts tend to be most severe on and near the crossing point, so that would probably be the biggest difference with those scenarios," he said.

Journey south will weaken system

The further south it goes, the weaker it is likely to be when it makes landfall.

If Narelle made it as far south as Perth, its visit would likely be as a category one system or even a tropical low, according to Mr Hines.

This is because of the three crucial ingredients a cyclone needs to survive and thrive:

Tropical Australia has these three ingredients in spades this time of year.

But as a cyclone moves further south, the concoction of prime conditions quickly starts to drop.

In the case of Cyclone Narelle, Mr Hines said the wind shear in particular would start to weaken as it moved south over the weekend.

"That will start to act to essentially pull the weather system apart," he said.

What strength Narelle will have when it is crossing into WA is still hard to predict.

While the Gascoyne could see a category three system, and the Central West a category two, Mr Hines said Perth was unlikely see a cyclone stronger than a category one.

'Unusual' direction behind Narelle's strength

Cyclone Narelle's journey across the top of Australia, instead of south, is part of the reason it's been able to maintain itself for so long without fizzing out.

Winds have steered the system almost directly west since it formed, keeping it in a prime cyclone zone. 

"That's pretty unusual," Monash University professor of tropical cyclones and atmospheric science Liz Ritchie said.

"A system that develops in the Coral Sea would normally start to feel a steering ... towards Brisbane perhaps, but not across the top of the country like TC Narelle has done."

'Brown oceans' fuel cyclones

Speed and the recent outback flooding also worked in its favour, according to Professor Ritchie.

Usually, when a cyclone passes over land, it weakens quickly because it does not have the energy of the ocean to support it.

But Professor Ritchie said Narelle had enough speed that it was not long enough over land to lose power.

She said it also passed over a very wet landscape, saturated by recent outback deluges, which helped fuel the system with moisture in a similar way to the ocean.

This phenomenon is referred to as the "brown ocean" effect.

"The land that it moved over is very wet at the moment because there's been lots of rain up there," she said.

"So when it moves over wet land, it can actually extract energy from that as well.

"It's not quite the same as it being over the ocean with the warm sea surface temperatures. But it's not as bad as if it had come in a bit further south over a dry land continent."

Has a cyclone ever hit Perth?

A cyclone crossing as far south as Narelle may do is rare in Western Australia, but not unheard of.

In 2021, Tropical Cyclone Seroja tore a path of destruction over the small tourist towns of Kalbarri and Northampton, in WA's central west, when it crossed as a category three system.

In 1989, Cyclone Ned crossed the coast near Perth as a category one, causing power disruptions and isolated roof damage in the Perth region.

And in 1978, Tropical Cyclone Alby seemed to defy logic, accelerating as it curved towards the coast, passing close to the far south-west corner of the state.

To this day, Alby is still regarded as the most devastating system to hit south-western WA, killing five people and helping fan bushfires across the region, even though it didn't ever cross the coast.

Some global studies suggest cyclones could trend further south in the future, due to climate change.

But Professor Ritchie said there was still a lot of uncertainty around those projections, particularly in Australia.

She said while the oceans were getting warmer, which favoured cyclones moving further south, changes to other crucial ingredients were not as well understood.

"[Sea surface temperature] is one of the ingredients that will help to maintain these cyclones further south," she said.

"But we also have to consider what the atmosphere is doing. And it's a little bit more uncertain about things like the vertical wind shear and the mid-latitude wind systems that affect how far tropical cyclones can actually go."