Another La Niña weather event is now even more likely to deliver a wet and windy summer across Australia, Bom says
The chances of a La Niña forming in next few months has increased from 50% to 70%, weather bureau warns
By Josh Taylor Tue 12th Oct 2021 https://www.theguardian.com/australia-n ... a-bom-says
It is now three-times as likely Australia’s summer period will be affected by storms and flooding, with the Australian Bureau of Meteorology (Bom) activating a La Niña alert on Tuesday.
Bom climatologist Dr Lynette Bettio said the El Niño–Southern Oscillation had been upgraded from La Niña watch to La Niña alert, meaning the chance of a La Niña forming in the next few months has increased from 50% in September to 70%.
“This is roughly three times the normal likelihood of an event forming in any year, but does not guarantee a La Niña will form,” she said.
“La Niña events increase the chances of above average rainfall for northern and eastern Australia during spring and summer, and the likelihood of one has been contributing to the bureau’s wetter-than-average outlooks recently.”
Weatherzone meteorologist Ben Domensino said in a blog post the La Niña would also typically produce more tropical cyclones during the Australian cyclone season from November to April.
“If we do see a fully-fledged La Niña forming in the next few months, this would be the first back-to-back La Niña event in a decade,” Domesino said.
The alert is not a guarantee it will occur, but an indication that the typical precursors are in place. The upgrade was made after continued cooling in the tropical Pacific Ocean and an increase in the number of climate models showing sustained La Niña conditions over summer.
Sea surface temperatures in the central Pacific Ocean are neutral but have cooled over the past three months and are supported by cooler than average waters beneath the surface.
Now six out of seven of the international climate models surveyed by Bom meet La Niña criteria from November.
The summer storm season warning has led to an increased focus on storm preparedness.
The NSW State Emergency Service commissioner, Carlene York, warned last month that the conditions during storm season – from October to March – could be similar to last year, including heavy rain and flash flooding. “We experienced major floods right across the state,” she said.
“In fact, it wasn’t long ago our volunteers responded to the major flooding event that overwhelmed communities across the Hawkesbury-Nepean, Hunter and mid-north coast. That event alone saw us respond to more than 14,000 requests for assistance, including more than 1,000 flood rescues.”
York pleaded with residents to prepare for storm season. “The more you can do now to prepare, the less likely you’ll end up needing emergency assistance from our volunteers when these weather events hit,” she said.
When the La Niña hit last year, Australia experienced its coolest summer in nine years, and wettest summer in four years, with 29% more rain than average.
Domensino warned last year the cooling impact of the La Niña masked the warnings on climate change.
“The cooling effect of La Niña, both in Australia and globally, can mask the background warming signal that’s occurring as a result of contemporary climate change,” he said.
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