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The hot days in Sydney and Melbourne this week are 8-10 degrees warmer than usual for early spring, while Septembers are warming in south-eastern Australia even faster than the rest of the year.
The highs of 29 degrees in Sydney on Tuesday and 24 degrees in Melbourne on Monday come as the landmark climate risk assessment released on Monday warned historical data was no longer a reliable guide to future risk.
More rain remains expected throughout spring as the Indian Ocean Dipole officially turned negative, while a La Nina event is likely – in part because of change in the way it is measured.
Qian Zhou, a climatologist at the Bureau of Meteorology, said a cold front was bringing cold, unsettled weather to the Southern Ocean, while forcing warmer weather on the other side of it.
“In front of the cold front are northerly to northwesterly winds, so that will drag the warm air from the north and the centre to the south and south-east, and also eastern Australia,” Zhou said.
Sydney’s hottest September day on record was in 2023, when it hit 34.6 degrees at Observatory Hill, Weatherzone figures show. In Melbourne, the record has stood for nearly a century, standing at 31.4 degrees in September 1928.
Melbourne’s hottest September on record overall was 2023, based on average maximum temperatures, while Sydney’s was 2013.
Across south-eastern Australia, the average temperatures for the first 25 years of this century have been 0.75 degrees higher than the 1961-90 average, an analysis of weather bureau figures shows. However, Septembers appear to be warming faster than the rest of the year – on average 0.9 degrees warmer than the long-term average.
Even when using the 1991-2020 baseline instead of the older 1961-1990 average, the warming trend in the 21st century is clear.
More to come
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