The Bureau of Meteorology has revealed when Australia’s third consecutive La Nina season will likely come to an end.
La Nina is continuing in the tropical Pacific and will likely persist into early 2023, increasing the chance of above average rainfall for northern and eastern Australia.
The negative Indian Ocean Dipole (IOD) event is also continuing, which means it’s more likely there will be above average spring rainfall for most of the eastern two thirds of the country.
When La Nina and negative IOD conditions combine, this also raises the likelihood of above average rainfall.
While the rain is set to continue for the time being, the BOM has predicted it will decline over spring before transitioning into neutral El Niño–Southern Oscillation (ENSO) conditions as summer comes to a close.
Based on current modelling, the BOM believes the phenomenon will be “a relatively short-lived event”.
Dr Agus Santoso of the UNSW Science’s Climate Change Research Centre said current modelling shows La Nina will likely peak sometime in November.
“In general, La Nina or, and also El Nino, tends to peak in summer itself and then starts to decay in autumn,” Dr Santoso told 7News.
“But this particular La Nina event (will) peak next month, in November, and then, it starts decaying from there on.
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“We should expect wetter than normal conditions.
“If we have extreme weather systems coming in, like what we had in March earlier this year, then that would lead to flooding because ... dams are already full and the catchments are already saturated.”
In its most recent Climate Driver Update on Tuesday, the Bureau of Meteorology said La Nina, a negative Indian Ocean Dipole (IOD), Southern Annular Mode (SAM) and approaching Madden-Julian Oscillation (MJO) were all contributing to the country’s torrential conditions this month.
“The Southern Annular Mode (SAM) is currently in a positive phase and is likely to remain generally positive throughout spring into early summer,” the BOM said in a statement.
“During the spring and summer months, a positive SAM increases the chance of above average rainfall for parts of eastern NSW, eastern Victoria and southeastern Queensland, and increases the chance of below average rainfall for western Tasmania.
“The MJO is moving into the western Pacific Ocean and is forecast to strengthen further in the coming fortnight as it tracks further east.
“Its influence at this time of the year may lead to above-average rainfall for parts of eastern Australia, and briefly reduce the strength of equatorial trade winds west of the Date Line.”
It comes as residents in Australia’s southeast are being warned to prepare for a massive rain band and flash flooding risk, which could isolate some Victorians for up to 72 hours and be “life-threatening” for Tasmanians.
Rainfall totals of up to 50mm are likely in southern NSW, north of the Victoria ranges, and northern Tasmania through Wednesday.
The weather is expected to worsen throughout Thursday in Victoria as the state braces for flooding, with up to 100mm of rain expected to fall in some areas.
Emergency services will be deployed to multiple regions including Wimmera in Victoria’s west, as well as residents along the Avoca, Loddon and Campaspe rivers.
In NSW, there are currently more than 80 flood warnings active across the state as of Wednesday, including three evacuation orders.
A severe weather warning for heaving rainfall and possible flash flooding has been issued for southwestern parts of NSW from Wednesday night through to Thursday.
Six-hourly rainfall totals between 30 to 50mm are likely, with isolated heavier falls up to 65mm.
Damaging wind gusts of around 110 km/h are possible over Alpine areas above 1500m from Thursday afternoon.
