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Weather shock as Perth and WA set to be hit with one of the year's most powerful storms

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A series of strong cold fronts is set to hit WA starting from Thursday evening.(Supplied: RAMMB)

A succession of powerful storms is set to deliver the kind of rainfall Western Australia typically experiences only once or twice during winter, with the worst of the severe weather expected over the weekend and Monday.

The first of the cold fronts will bring widespread and potentially heavy falls late on Thursday and into Friday, but the second front that will arrive on Saturday and the third on Monday will produce the strongest winds.

"The sort of rainfall that we're experiencing over the period of time probably only occurs around once or twice in a winter season," said Bureau of Meteorology (BOM) spokesman Neil Bennett.

"So it's not your normal run-of-the-mill front and it is going to be delivering a lot of rain to a large area of Western Australia."

The combination of extremely dry conditions and gusty northerly winds ahead of Thursday's front produced severe fire conditions which led to an out of control bushfire that closed the Kwinana Freeway in the southern Perth suburb of Baldivis.

But even stronger squalls are expected on Saturday.

The weather bureau says the expected rainfall is the type usually only seen once or twice each winter.(ABC News: Greg Pollock)

"We could see winds in excess of 90 kilometres per hour. If that's the case a warning will be issued and those types of winds can typically cause damage to buildings, bringing down small trees, those sorts of things," Mr Bennett said.

"At this time of the year we've had such a long dry spell and the soil is very, very dry, so trees are susceptible … very often the first storm of the season is the one that brings down a lot of trees."

How much rain can we expect?

After Perth's second driest May on record, with only 17.8 millimetres collected during the entire month, the city is expecting to notch up more than 50mm over the next few days.

Thursday's cold front will drag moist tropical air from the north-west over much of the southern half of WA, bringing widespread falls to farming areas that are desperate for rain.

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The bulk of the falls will come late on Thursday and into Friday morning.

"It's expected to deliver some quite significant rain for a very dry WA. We've just had the driest year to date for the south-west of WA on record," Mr Bennett said.

"The rainfall itself will be very welcome in agricultural districts — many parts will receive falls up to double digits."

But with another two fronts close behind, showers will continue until early next week.

"Some of the falls up through the Mid West cumulatively over the next three or four days, as well as the South West, could be in excess of 50mm," Mr Bennett said.

"The farming communities are absolutely hanging out for this, we'd like to think that this will help.

"This is a good start, let's just hope that we can see some follow-up rain because the follow-ups are desperately needed.

"If this is the only rain that we get for three to four weeks, then this will really put a dampener on everything that they've been hoping for with this particular rain event."

People are being urged to stay inside during the worst of the weather if possible.(ABC News: Andrew O'Connor)

Storms, squally winds, pea-sized hail

The brunt of the stormy weather is expected from Saturday through to Monday, with damaging winds, heavy falls and hail a risk.

"We would be expecting to see pea-sized hail, that is the typical [winter] size … some strong squally winds and there is always the risk with those squally winds that we could see some damage," Mr Bennett said.

"We would start to issue warnings if the wind speeds were 90kph or more and it is possible we will see those on the Saturday and again on Monday, so we will be keeping a close eye on that.

"Temperatures are going to be completely different to those that we experienced last weekend, we're looking at temperatures of 14 to 15 degrees Celsius by Tuesday."

Department of Fire and Emergency Services Assistant Commissioner Brad Stringer urged people to prepare their homes by securing loose items, trimming tree branches and clearing out gutters.

"With this storm event if you can do the best that you can to be self sufficient that would be fantastic for us because our responders may be stretched as we go forward," he said.

"If you don't need to be outside or driving in a car, please stay inside and be in a secure place. There may be some localised flooding … if you don't need to be out at the height of the storm it just makes it a lot easier for emergency responders to deal with one less issue."

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