Hottest September day in years forecast in parts of south-eastern Australia as ‘spring rollercoaster’ sets in

Australians in the nation’s south-east are expected to experience the warmest September day in years, with temperatures rising 6C to 12C above average over the weekend.

Coastal areas are expected to reach the high 20s while inland regions will extend into the low to mid 30s, as a cold front in Western Australia and a high-pressure system in the Tasman Sea drag warm, dry and sunny weather towards south-eastern Australia, Bureau of Meteorology senior meteorologist Dean Narramore said.

On Sunday, Canberra and Melbourne are expected to record their highest September temperatures since 2023, with the Victorian capital set to reach 27C.

Sydney is forecast to reach 28C on Sunday, while Hobart is set to record its hottest September day in seven years.

Though Narramore said these were some of the warmest September temperatures in years, things were expected to get both hotter and colder before the month ended.

“We’re going to see cooler conditions Monday and Tuesday, but then we could see an even bigger burst of heat probably late next week and into next weekend for much of the same part of the country,” he told Guardian Australia.

These fluctuations were common at this time of year, Narramore said, pointing to Hobart as a good example of the “spring rollercoaster”.

The Tasmanian capital is forecast to hit 27C on Sunday, before almost halving to 14C on Monday.

“We get these really hot, northerly gusty winds and then these cooler southerly winds behind it, which give a big shot of colder air across the country,” he said.

“But because they’re so fast moving, the next system comes in pretty quickly and that’s why we see these northerly winds return and we go back into those well-above-average temperatures.”

The upcoming warm weather will likely be hotter than temperatures this weekend, but also be more prolonged and widespread.

Most of south-eastern Australia was expected to run anywhere from 8C to 15C above September averages from Thursday, Friday, Saturday, and possibly beyond that, according to Narramore.

The BoM’s spring outlook is warm and dry. A strong El Niño developing in the Pacific Ocean is forecast to peak in late spring or summer and “reach levels above the warmest observed since reliable records began in 1950”, according to the BoM.

In Australia, El Niño events increase the chances of warmer, drier weather and fire danger in summer, particularly in areas that are not getting rain, like Queensland and New South Wales. They can also increase the risk of heatwaves, drought and bushfires.

As a result of the El Niño, 2027 is expected to be the hottest ever year globally.

Fire danger was currently high in some parts of the country, but there was nothing too extreme yet, Narramore said.