South-eastern Australia is set to experience its warmest September day in years, with temperatures soaring 6°C to 12°C above the monthly average over the weekend, according to the Bureau of Meteorology (BoM). Coastal areas are forecast to reach the high 20s, while inland regions will extend into the low to mid 30s.
Weather Systems Drive Unseasonable Heat
BoM senior meteorologist Dean Narramore attributed the warm, dry and sunny conditions to a cold front in Western Australia and a high-pressure system in the Tasman Sea, which are dragging heat towards the south-east. On Sunday, Canberra and Melbourne are expected to record their highest September temperatures since 2023, with the Victorian capital set to reach 27°C. Sydney is forecast to hit 28°C, while Hobart is set to record its hottest September day in seven years.
Narramore told Guardian Australia that while these are some of the warmest September temperatures in years, conditions are expected to fluctuate wildly before the month ends. “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 said.
The 'Spring Rollercoaster' Effect
These fluctuations are typical for this time of year, Narramore explained, using Hobart as a prime example. The Tasmanian capital is forecast to hit 27°C on Sunday, before almost halving to 14°C 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 is likely to be hotter than this weekend’s conditions, as well as more prolonged and widespread. Most of south-eastern Australia is expected to run anywhere from 8°C to 15°C above September averages from Thursday through Saturday, and possibly beyond, according to Narramore.
El Niño and Long-Term Outlook
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 not receiving rain, such as Queensland and New South Wales. They can also heighten the risk of heatwaves, drought, and bushfires.
As a result of the El Niño, 2027 is expected to be the hottest year ever recorded globally. Currently, fire danger is high in some parts of the country, but Narramore noted that nothing too extreme has been observed yet.
