Australians endured the country’s third-hottest summer on record, while odds strongly favour a hotter and drier than usual autumn, the Bureau of Meteorology has said.
The top-three ranking applied for each of the maximum, mean and minimum temperatures. All states and territories bar Victoria reported one of their 10 warmest summers.
Mean temperatures, which average out daytime and night-time readings, were 1.62C above the bureau’s 1961-1990 yardstick. Only the 2018-19 and 2019-20 summers were warmer, meaning Australia’s three hottest seasons have occurred in the past six years.
And, voila, also Australia's third-hottest on record for mean temperatures, @bom_au says... pic.twitter.com/0sfqGqxsgv
— @phannam@mastodon.green (@p_hannam) March 1, 2024
Western Australia set a record for its summer mean temperatures, topping 2019-20.
“We did reach the bureau’s threshold for at least low-intensity heatwaves across pretty much all of Australia at some point during the summer,” said Simon Grainger, a senior bureau climatologist. “But really for eastern Australia it was a lot more about the steady heat.”
Australia’s weather is driven by conditions in surrounding oceans as well as the background warming from climate change that has elevated temperatures by about 1.5C since 1910.
Much of the media attention focused on the development of an El Niño pattern in the Pacific. Such an event, however, tends to have its strongest influence on rainfall in eastern Australia in the spring rather than the summer.
Of the 28 years with an El Niño event since 1900, the summer of 2023-24 was the third wettest, trailing 2009-10 and 1994-95, Grainger said. Rainfall averaged 247.7mm across the country, or almost 19% more than the 1961-90 norm.
By rainfall, summer had 19% more rain than average for the season (vs the 1961-90 average). (Source: @bom_au) pic.twitter.com/SOv7MEzwf7
— @phannam@mastodon.green (@p_hannam) March 1, 2024
The unusual feature was a persistent positive phase of the so-called southern annular mode in December and January. During summer, that pattern means eastward moving weather systems tend to track closer to Antarctica.
“What you do see in those situations [is] easterly flows bringing those muggy conditions and a chance of storms to eastern Australia,” Grainger said. Warmer than usual sea-surface temperatures in the Tasman also contributed to extra rain.
Among the major capitals, Brisbane has started 2024 with the longest streak of overnight temperatures at or above 20C, counting 61 so far with more to come. The previous record was 59 to kick off 1978, he said.
Sydney, meanwhile, reported its third hottest summer on record by mean temperatures, according to Ben Domensino, a senior Weatherzone meteorologist. The city’s mean reading of about 24.1C was slightly more than 2C above the long-run norm.
Abnormally high dew point temperatures were a feature of summer in eastern New South Wales “making it harder for the body to lose heat by evaporating sweat”, he said. Sydney’s summer rainfall of 411mm was also about 80mm above average.
Perth was another standout city, with the Western Australian capital notching its second hottest summer on record for maximum temperatures, Domensino said.
The average daytime high of 32.6C was beaten only by the 2021-22 summer’s 33.3C average. It also clocked a record seven days above 40C in February, beating Perth’s record of six such days set in January 2022, Weatherzone said.
Victoria was the stand-out exception for rainfall, with a particularly dry month in February. Average rainfall was just over 12mm for the state, or well below the average of 31mm. The bushfire season may have a ways to run. (Via @bom_au) pic.twitter.com/Ruix07rbBY
— @phannam@mastodon.green (@p_hannam) March 1, 2024
Melbourne was one capital to post a slightly lower than average summer for maximums. Temperatures, though, picked up in February, while rainfall dwindled to just 6mm for the month, Domensino said.
The shift towards drier conditions may continue into autumn, according to the bureau’s latest outlook, released on Thursday.
As for what's ahead, @BOM_au sees the odds favouring a drier than average autumn for most of the country, particularly in the east: pic.twitter.com/jOLZLKgnWO
— @phannam@mastodon.green (@p_hannam) March 1, 2024
The eastern two-thirds of the country has odds favouring below-average rainfall, Grainger said.
Temperatures were also tilting towards warmer than normal conditions for the March-May period. Those odds were 80% or higher for maximums to be above-average for much of the nation, he said.
Similarly, the odds favour a warmer than average autumn too. For maximum temperatures, those chances exceed 80% for most of the country. (With the background warming from climate change, this pattern is pretty common to see.) (Via @bom_au) pic.twitter.com/R1JIOWI9sH
— @phannam@mastodon.green (@p_hannam) March 1, 2024
Grainger said uncertainty beyond autumn meant that it was too early to be sure whether another La Niña event may form in the Pacific later in the year.
