Australia Weather News

Weather forecasters say one-third of Western Australia may receive rain due to a "once-in-a-decade" storm, as the remnants of ex-Tropical Cyclone Mangga impact the coast.

A severe weather warning is in place south-west of a line from Onslow to Esperance, but the Bureau of Meteorology (BOM) said it was still too early to pinpoint exactly which towns would be most severely impacted.

The worst of the incoming wild weather is forecast to hit the north-west coast this afternoon, before the storm heads further south towards Perth.

BOM forecaster Jessica Lingard said wind gusts were increasing at coastal towns — including Carnarvon and Exmouth — as the leading edge of the system began to move through, and conditions were expected to worsen further south as the day continued.

But Ms Lingard said a deep, low-pressure system coming in from the south was forecast to cause hazardous conditions in the south-west tonight.

"We are going to expect to see a couple of smaller low-pressure systems forming off the west coast and anywhere around wherever those lows form, we'll start to see some gusts that could reach up to 130kph," Ms Lingard said.

"They'll be mostly coastal locations, but we will be seeing some stronger wind gusts inland as well."

Heavy rainfall of up to 100 millimetres, plus abnormally high tides, are also forecast.

"We are looking to see rain across much of the western third of the state, coastal areas are obviously going to see a little bit more than those inland," Ms Lingard said.

Residents urged to prepare

Ex-Tropical Cyclone Mangga was downgraded to a tropical low in the early hours of Saturday morning as it moved south-west of the Cocos Keeling Islands and towards WA's north-west coast.

The storm is expected to produce destructive winds of up to 130 kilometres per hour, heavy rainfall and unusually high tides to over 1,000 kilometres of coastline as it travels south from Sunday morning until Monday.

BOM state manager James Ashley said the breadth of the warning area was unusual, spanning from Karratha to Esperance, including Perth.

"This is a really rare event for WA," he said.

"Not only is it unusual for the time of year, it extends across a large part of the state."

In Perth, the wet weather is forecast to continue throughout the week.

Mr Ashley said it was difficult to pinpoint exactly which areas will be hardest hit by the storms.

"The message is that the whole west coast is at risk with this event, we're expecting to see multiple centres," he said.

"While one system might impact the northern half of the coast, another system might impact the south-west."

Department of Fire and Emergency Services (DFES) acting assistant commissioner Jon Broomhall said people need to act now to secure their homes.

"Normally, our storms come from the south-west," he said.

"This is going to come from the north-west so it'll test people's buildings, sheds, and all those unsecured items.

"We're asking people to secure property, make sure everything loose is tied down."

Mr Broomhall also warned people not head out on the water.

"We don't need our marine rescue volunteers' lives put at risk by people making silly decisions to go boating or surfing in these conditions."

Waves along the coast are expected to reach up to 8 metres high, likely causing widespread beach erosion.

Fire bans are also in place for the southern half of WA, with people told to halt any back-burning programs they had scheduled at their properties.

"We don't want fires running and a storm at the same time," Mr Broomhall said.

"So please, extinguish your planned burn now."

Crews anticipating power cuts

Electricity distributor Western Power said its crews were preparing for potentially significant outages and disruption to the grid.

"No matter what happens, we're ramping up our crews in preparation to respond to whatever this storm does produce in the way of outages," Western Power spokesman Paul Entwistle said.

Specialist crews would be ready to assess any power hazards reported by the community, Mr Entwistle added.

"During the storm, if you do see a fallen power line or any damage to the network, please stay 8 metres clear at least, and make the safe call to Western Power on 13 13 51," Mr Entwistle said.

He also said people should check their yards for any items or branches which could be flung into power lines during the storm.

Drivers heed weather warning

With intrastate borders now open, crowds had been expected on highways leading out of Perth but the severe weather warning caused many to revise their plans.

Mr Broomhall said people should avoid travelling during the storm, particularly Perth holiday-makers who had travelled to the South West.

"I understand people want to get out and about but the advice is to travel home early," he said.

"Absolutely try and get back home as soon as you can."

Jonelle Jones, manager of the Crooked Carrot cafe on Forrest Highway south of Perth, said most customers had told her they planned to be off the road by Sunday morning before the storm hit.

"[Drivers] are concerned, so they are going to go home and make sure everything is tied down," she said.

While Sunday was expected to be quieter at the cafe, Ms Jones said the early part of the weekend was very busy.

"Roads are back to some sort of normal," she said.

"It's amazing to see it so busy, so quickly."

She said customers had been telling her they just wanted to be on the road — "just to be free again" — after travel restrictions were lifted.

"There's a lot visiting family, that has probably been the biggest [reason for travel], is getting back to see their family," Ms Jones said.

Mandurah resident Bev Baldwin was travelling to Margaret River and Augusta to go electric biking with her family, but decided to scale back the trip ahead of the storm.

"We were thinking of going down for the weekend, but we decided not to go for the whole weekend, we're just going to go for the day," she said.

"It's just nice. When you know you can't do something, you just think 'oh, but I want to do it'."

New historical COVID-19 cases

No new COVID-19 cases were recorded in WA on Saturday, almost a week after restrictions were eased.

There are no longer any confirmed cases in regional WA after a patient in the Goldfields recovered.

There are just two active coronavirus cases left in WA — both are recovering at home in Perth.

However, WA's total number of cases was revised up to 560 after three historical cases were identified through blood tests.

Two of the cases, which were connected to cruise ships, had already recovered from the disease when they entered WA.

The remaining case was a returned overseas traveller, who had contact with a known case and self-isolated when she became ill.

The Health Department said the historical cases were no longer infectious and therefore posed no risk to the public.