Parts of Australia’s outback are receiving months’ worth of rain over a couple of days as an unusual and extensive rain event douses what’s typically the dry season.
Southerners hoping to escape the winter chill in Broome have instead been soaked in 30mm of rain in the 24 hours to 9am Tuesday, or the most in a single June day in a decade, according to Weatherzone. Monday’s top temperature was barely above 25C – four degrees cooler than a typical June day in the Kimberley coastal town.
Yulara airport, near Uluru, collected 64.6mm of rain over the 48 hours to 9am on Tuesday – the wettest pair of June days since 2004 and almost quadruple the June average.
Other locations including the Kimberley’s Gibb River were unseasonably wet. It received 72mm of rain during the same period, making it the second wettest winter day in records going back 101 years, according to Weatherzone. That tally was seven times the June norm.
The moisture is coming from a massive cloud band that formed over north-western Australia and will transport rain over much of the interior for days to come.
Maryam Al-Ansari, a weather risk analyst at Weatherzone, said the rainfall’s extent may be largest on Wednesday and Thursday before the system starts to recede.
Development of the northwest cloud band ⬜️🟩 currently over Australia. A new upper low 🟨 emerging south of WA is expected to produce a second cloud band on the weekend, with the rainfall focus likely to be NT and QLD. pic.twitter.com/pzEWAHnUHb
— Andrew Miskelly (@andrewmiskelly) June 27, 2023
“It requires particular conditions that don’t usually align together to occur,” Al-Ansari said, adding: “It’s quite a substantial event.” Tropical moisture from the Indian Ocean is combining with a cold pulse of air from the Southern Ocean and strong upper-level winds.
Miriam Bradbury, a senior meteorologist at the Bureau of Meteorology, said a large high-pressure system over eastern Australia was “acting like a blocker”.
“That means we have this river in the atmosphere extending from the northwest all the way down towards the southeast [of Australia that] can’t properly move east because that high pressure system is there,” Bradbury said. “It’s just continuing to drag that moisture down south and that really just gives it the potential for these really widespread, impactful rainfall totals.”
While big bursts of winter rainfall over central Australia aren’t common in the cooler months of the year, they are also less likely when conditions in both the Indian and the Pacific oceans have been tilting towards their drier phases – at least for Australia.
Last month was Australia’s second driest May on record, with rainfall just over a fifth of the average for the month, according to the Bureau of Meteorology.
The positive phase of the Indian Ocean dipole – a measure that tracks sea-surface temperature differences across that basin – is expected to be reached within months, the bureau has said. Hot on it heels is likely to be an El Niño event in the Pacific, adding to the generally drier-than-usual outlook for most of the country.
“The ocean hasn’t cooled [around Australia] as much as we thought it would,” Al-Ansari said. “It’s definitely something that we did not foresee.”
Rainfall totals may approach 100mm in some parts of central Australia, triggering flood watches for regions in inland Western Australia and for southern and western parts of the Northern Territory.
The rainfall will then shift eastwards to central and northern Queensland, also regions that would typically receive little rain at this time of the year. The system will be replenished by moisture drawn from waters off Australia’s north.
“We are going to see some of that rain starting to push into New South Wales tonight going into tomorrow, but it’s going to tend to be much patchier,” Bradbury said. Rainfall totals in NSW and parts of inland Queensland “are generally going to be lower than what we’ve seen through those more central parts of the country”.
Inland rain over the next eight days (on top of some sizeable falls already)...perhaps the last big falls before the +IOD and El Nino set in..? pic.twitter.com/lnO8a1WN1C
— @phannam@mastodon.green (@p_hannam) June 26, 2023
“The timing of it is quite unfortunate [with] a lot of people on the roads, not just through Queensland but through the Northern Territory and into the Kimberley as well given it’s the school holidays,” Bradbury said. “We recommend everybody keeping an eye on the forecasts and warnings to make sure they’re up to date.”
Al-Ansari said while the climate drivers look likely to resume their drying pattern in coming weeks, particularly if an El Niño forms, it was not out of the question that more belts of rain might penetrate well into Australia’s red centre again this winter.
“With global warming, things are becoming less predictable,” she said. “I wouldn’t say this could be the last [big wet] event that we will see.”
Among other regions reporting unusually large rain totals is Siddins Creek. The WA outpost typically receives just 0.4mm in June and has collected 73.4mm in the past three days.
Curtin Springs in the Northern Territory received 55.2mm of rain in the past two days, or about four times the average June total.
