Anomalous weather events behind absence of 40C days in Perth this summer

Perth was drenched by nearly 100mm over a weekend in January.
Perth was drenched by nearly 100mm over a weekend in January.

THE typical WA summer is fraught with 40C days, with people of Perth either at the beach cooling down, hibernating under the aircon or on Facebook complaining like they’ve never experienced heat before (you know who you are).

However, today is the last day of summer and for the first time in 16 years, Perth hasn’t had a 40C day.

It’s the second year in a row where we’ve seen extraordinary weather events, with high amounts of summer rainfall, mild temperatures and flooding, which saw fishers catching carp in a park.

Bureau of Meteorology senior climatologist Glenn Cook said Perth was below average for median temperatures for the 2017-18 summer, but last year had milder weather on average.

He said the decade prior to 2016 had been particularly warm, so the weather over the past two summers was extraordinary.

“We are seeing stronger wet season rainfall in the northwest of WA, which is impacting rainfall in the southwest of the state, causing a number of the weather events we saw earlier this month and last summer,” he said.

“December and January was much wetter than normal, with 147mm falling this summer in the Perth metro, which is the fourth highest summer rainfall on record; last year we recorded the highest.”

Mr Cook said he didn’t believe the milder weather would become a trend.

“I think it’s just an anomaly in our climate over the past two years, I don’t think it will become a trend,” he said.

“Typically we are seeing a warmer climate, so this weather over the past two years has been interesting.”

UWA Professor of Coastal Oceanography Charitha Pattiaratchi said the milder temperatures had been caused by a prevalence of southerly winds, bringing colder temperatures to WA.

“Over the last two years we have been neutral, with southerly winds bringing cold air from the south and colder ocean temperatures,” he said.

“This is not part of climate change, but climate variability, so it’s not likely to continue and we could possibly see a stinking hot weather next summer.”

Prof Pattiaratchi said high pressure systems off the Great Australian Bight were the reason for warmer temperatures in WA.

“The passage of weather systems has caused the southerly winds we have been experiencing, “ he said.

“Long periods of hot weather occur when high pressure systems are constantly stuck in the Bight, causing easterly winds and warmer weather.

“In the past two years these pressure systems haven’t been stuck, they have still come through but they haven’t been stuck, so that’s why we’ve had some warmer days, but overall a lot milder on average.”

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