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Perth's back-to-back cooler summers belie warming trend, say forecasters

Rebecca Dollery, Wednesday February 28, 2018 - 17:26 EDT
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Perth saw its fourth wettest summer ever, with 147mm recorded between December and February. - ABC

While its counterparts in the east sweltered, Perth had one of its mildest summers in 18 years, recording just 10 days over 35 degrees Celsius.

Residents in the WA capital can normally expect about 20 days where the temperature reaches 35C or higher, and three or four days hotter than 40C.

However the hottest day this summer, January 14, was a mere 38C — the lowest maximum since the summer of 2001-02.

Sydney, Adelaide, Melbourne and Canberra all recorded higher summer maximums, with each experiencing days exceeding 40C.

Sydney sweltered through the hottest day of the season, with a top of 43.4C, its highest temperature in 79 years.

The average maximum for Perth this summer was 30.2 degrees, half a degree below the average since recording began at the Mount Lawley weather station 25 years ago.

The long-term average for the city is 29.3 degrees.

It has also been Perth's fourth-wettest summer, after heavy falls from ex-Tropical Cyclone Joyce dumped 96.2mm in the gauge on January 16, bringing the summer total to 147 millimetres.

Colder summers go against trend

The Bureau of Meteorology's Glenn Cook said the cooler weather was partly due to the mobility of weather systems to the south.

"We've had high-pressure systems moving fairly steadily to the south and not sitting in the Bight for any length of time," he said.

"Hotter summers will usually have more easterly winds and more static high pressure systems in the Bight, building up heat over the west coast."

Perth's wetter, cooler summer is the second in a row for the city.

2016-17 saw a record wet summer, with 192.8 millimetres of rain over three months, exceeding the previous record of 180.4mm set in 1954-55.

It was also a season of mild daytime and overnight temperatures.

Several sites across the metropolitan area had their lowest daily maximum temperatures ever on February 9, 2017, with temperatures in the 13-18C range.

Mr Cook said the past two years were not likely to indicate a cooling trend for Perth.

"Perth's certainly seen a warming trend over the last 100 years or so, pretty much like most of the globe, in fact," he said.

"And prior to these relatively mild summers, the previous nine were all above average.

"So we are certainly seeing a warming trend, and I think this is just a bit of variability that we're seeing."


© ABC 2018

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