When the spring and summer months bring sweltering weather to Australia’s east coast, sudden relief can come in the form of a “southerly buster”, an abrupt southerly wind that can drop the mercury in minutes.
Global heating is increasing the frequency of these gale-force wind changes on the south-eastern seaboard, which can disrupt flights, create hazardous sea conditions, and increase bushfire danger.
Here’s what you need to know.
What is a southerly buster?
Known to locals in Australia’s south-east as southerly busters, these sudden wind changes tend to occur from October to March. A hot north-westerly wind turns southerly, with wind gusts that exceed 54km/h.
A buster can bring thunderstorms and drop temperatures by up to 20C within minutes. When a buster is intense, it can be visible as spectacular clouds that roll in perpendicular to the coast.
HAPPENING NOW: Incredible timelapse of the strong southerly buster surging through the #GoldCoast right now. #SurfersParadise @BOM_Qld pic.twitter.com/FKntoJbflW
— myGC.com.au (@myGoldCoast) December 18, 2016
Southerly busters form when a shallow front of cold air comes up against the Great Dividing Range. “Because of the orientation of the topography, it slows down over the land because of friction and then it pushes up the coast because it gets trapped,” says Dr Milton Speer, a visiting fellow at the University of Technology Sydney’s school of mathematical and physical sciences.
Southerly busters occur along the coast of New South Wales and can extend as far north as Brisbane, Speer says.
They also occur up the east coasts of South America and South Africa, as well as New Zealand’s South Island, but are referred to by different terms elsewhere, Speer says. “The topography plays a similar part [there]”.
How is global heating changing southerly busters?
In research published this year, Speer and his colleagues found that global heating had increased the frequency of southerly busters over the last three decades.
Analysing data from 1970 to 2023, they found that before 1995, the busters that occurred were mostly severe – defined by wind gusts greater than 74km/h.
From 1996 onwards, the number of less severe busters began to increase, shooting up dramatically between 2017 and 2022.
“While those severe ones haven’t decreased, there have just always been very few of them,” Speer says. “You’ll see typically one to two per year before the 1990s, and from 1990s the weaker ones gradually pick up.”
There was a huge increase in the frequency of weaker southerly busters over the triple La Niña years of 2020 to 2022, he adds. “It’s just that people didn’t notice them.”
“We’ve had a couple in October and November and one came through overnight and I didn’t notice any gusts at all.”
While southerly busters can provide cool relief after a heatwave, Speer and his colleagues warn that their increasing frequency may make it more dangerous for planes taking off and landing, for people swimming and in boats, and could elevate bushfire danger and also the chances of wind damage to coastal property.
Is increasingly extreme weather making predictions harder?
Extreme weather including heatwaves and flash flooding are increasing in frequency globally. These extreme events are considered rare and severe in the context of a region’s “typical” climate.
Meteorologists usually define a region’s climate using a 30-year average of mainly rainfall and temperature data. But Speer suggests that extreme short-term climate variations are making these 30-year averages less useful as a baseline comparison of what is normal.
New research he co-authored, published in the journal Academia Environmental Sciences and Sustainability, suggests that scientists need to update their climate models to provide more accurate seasonal and annual rainfall and temperature forecasts.
Because extreme variations are now occurring in periods of a decade or shorter, big changes can inadvertently be hidden in averages over longer periods. “The averages of extreme events – [for example] no rain versus a hell of a lot of rain – they can cancel out over 30 years,” Speer says.
The study’s authors suggest that different regions may need to come up with their own shorter climate time periods to more accurately forecast extreme weather events in future.
