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ABC News

Perth goes through entire summer without recording 40-degree day

Perth got through summer without a day over 40C. (ABC News: Kenith Png)

Perth's summer has been described as one to "savour", making it through the full season without hitting 40 degrees.

But residents are being warned the heat isn't over yet, with the city and west coast at the beginning of a heatwave, the first to reach severe category this year.

Summer of 2022-23 marks a strong contrast to last year, when tumbling heat records became common place, including a record number of days above 40 degrees Celsius and a record number of consecutive days above 40C.

Last summer was an unusually hot one for Perth and much of the state. (ABC News: Kenith Png)

Typically, Perth experiences three to four days over 40C mark — one per year in December, one to two per year in January and one in February.

Extreme heat more common

The Bureau of Meteorology's (BOM) Jessica Lingard said it was "unusual" to go the full summer without 40, but "not unheard of", having happened three times since records at the Mt Lawley site began.

The last time it occurred was five years ago in 2016-17. It also happened in 2001-2002 and in 1998-99.

But she said climate change was making days of extreme heat more common.

A 1C increase in average global temperature over the last century has already more than doubled the days over 40℃ in Perth, according to research.

"The trend of climate change is that we are going to see more of these hot day, warmer periods and heatwaves down the west coast," she said.

"Similar to what we saw last year, that's what we can expect.

"So you've got to take the good with the bad and this has got to be a good year."

BOM forecaster Jessica Lingard says climate change is making extreme weather more common. (ABC: Greg Pollock)

The city came close to reaching 40C on two occasions, in early February and mid-January, when it reached 39C.

"That's the closest we've come in the metro," she said.

"So we did see some 40s up in the hills and the north-eastern suburbs did catch a couple of 40 degree days too."

But Ms Lingard said despite the lack of 40C days, the city's average temperature still finished slightly above average.

She said the difference this year boiled down to the speed heat driving weather systems moved from west to east.

Weather systems 'doing what they are supposed to'

During summer, Perth's warm weather is generally set up by the combination of a high-pressure system south of the state and a west-coast trough, which fan-force the city with hot desert winds from the north-east.

Despite the lack of 40C days this summer, the city's average temperature still finished slightly above average. (ABC News: Kenith Png)

"This year, the [weather systems] are doing what they're supposed to do," Ms Lingard said.

"They form on the west coast, they hang around for maybe a day or two, and then a nice ridge of high pressure develops and pushes them east-wards."

She said last year, the heat driving systems "got stuck" for days on end.

"Last year, what we saw happening was that these troughs were forming, but they weren't moving on," she said.

"They were hanging around for four days, five days, even longer."

First severe heatwave of the season

Perth is going through its first severe heatwave this week with the maximum temperature reaching 36.7 today, while a top of 37C is forecast for Wednesday and Thursday, with a slight drop expected on Friday with a top of 35C.

Ironically, a weather set-up more reminiscent of last year's lingering systems will be present for the first week of Autumn.

Last summer Perth recorded 13 days over 40 degrees, but this summer the city has not hit the mark.  (ABC News: Cason Ho)

Temperatures are expected to hit the high 30s along the west coast, from Monday until Friday with a heatwave warning issued for the first time this summer.

Ms Lingard said it would not reach the same extremes of last summer.

"For the most part, the Perth metro is just in low intensity heatwave," she said.

"But the warning covers the entire metro area.

Very hot conditions during the week are expected to cool signficantly for the weekend. (ABC News: Kenith Png)

"It is the first [severe] heatwave we've seen for the lower west this year."

Cooler conditions are expected over the weekend.

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