‘Triple dip’ La Nina for wetter-than-usual spring

The weather bureau's outlook for spring 2022

Source: Bureau of Meteorology

The likelihood of another wet spring and summer just got worse for millions of Australians, with one of the world’s leading weather forecasters warning of a ‘‘triple dip’’ La Nina on the way.

The World Meteorological Organisation says there is now a 70 per cent chance of another La Nina forming in coming weeks, bringing a greater chance of higher-than-average rain across much of Australia between now and February.

If the United Nations weather agency’s forecast comes true, it will be the first time this century that there has been a La Nina in three consecutive northern hemisphere winters – something known as a “triple-dip” La Nina.

The WMO report says the current La Nina, which started in September 2020, is likely to last another six months.

Australia has experienced a triple-dip La Nina only three times since 1900: From 1954 to 1957, from 1973 to 1976 and from 1998 to 2001.

The WMO report gives a 70 per cent chance of higher-than-average rainfalls for Australians living near the east coast, gradually decreasing to 55 per cent between December and February 2023.

Lismore, which is located on a low flood plain on the banks of Wilsons River in northern New South Wales, flooded every time there was a La Nina event in the 1950s, 1970s and early 2000s.

This year alone, Northern Rivers residents endured three major floods that destroyed homes and businesses across the region.

A service station is inundated by flood water on March 30 in Lismore. Photo: Getty

La Nina conditions, which bring a greater chance of rainfall, strengthened in the tropical Pacific as trade winds (winds that blow from east to west around the equator) intensified from mid-July to mid-August affecting temperatures and increasing the chances of drought and flooding in different parts of the world.

For Australia, that means the east coast will endure heavy rainfalls and floods again with the third La Nina season.

It follows a similar report last month from the Bureau of Meteorology that upgraded its El Nino-Southern Oscillation (ENSO) outlook to a La Nina “alert” – a final stage before an actual La Nina event is declared.

Bureau of Meteorology senior climatologist Dr Lynette Bettio said spring rain would bring a risk of flooding for eastern Australia.

“Where soils and catchments are wet, and streamflows are high, further rainfalls this spring will increase the risk of flooding for eastern Australia,” she said.

“In northern Australia, the first rains of the wet season are likely to be earlier than normal for much of Queensland and the Northern Territory.

“October is the official beginning of the wet season across northern Australia.”

La Nina Australia

Probabilistic forecasts of surface air temperature and rain for the season September-October 2022. The baseline period is 1993–2009. Photo: World Meteorological Organisation

The Bureau of Meteorology also reported a positive Southern Annular Mode (SAM), which during the spring season has a drying influence for western Tasmania and Western Australia but a wetter influence for parts of eastern New South Wales and far east Victoria.

WMO Secretary-General Professor Petteri Taalas says the effects of La Nina will vary in different parts of the world.

The worsening drought in the Horn of Africa and southern South America bear the hallmarks of La Nina, as does the above-average rainfall in South-East Asia and Australasia,” Professor Taalas said.

“The new La Niña Update unfortunately confirms regional climate projections that the devastating drought in the Horn of Africa will worsen and affect millions of people.”

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