BOM set to declare La Nina event as east coast braces for rains, floods and cyclones

The Bureau of Meteorology is expected to announce a La Nina event on Tuesday which could increase the risk of widespread flooding and severe tropical cyclones across Australia this summer.

Parts of NSW are already experiencing heavy rains and floods, while the first tropical cyclone of the 2021-22 season is strengthening off the coast of Western Australia, 400 kilometres south-east of Christmas Island.

In the coming week some parts of NSW, Queensland and Victoria are likely to see between 50 and 100 mm of rain, which will place pressure on already-brimming waterways.

Australia is likely to see heavy rainfall, floods and tropical cyclones this summer with a La Nina event set to be declared on Tuesday.Credit:Nick Moir

A La Nina alert has been in place for several months, meaning there was a 70 per cent chance of an event developing. This prediction is likely to be upgraded by the BOM at 1pm.

What does La Nina mean?

A La Nina phase is caused by stronger trade winds changing ocean surface currents, which draws cooler water from below. The winds also help pile up warm surface waters in the Pacific Ocean, meaning the area becomes more conducive to above-average clouds and rainfall across Australia, and a more active than normal tropical cyclone season (which can also bring rain far inland or down the eastern coast).

A La Nina can linger for two years. Weatherzone senior forecaster Ben Domensino said the last significant consecutive La Nina events occurred in 2010-2012 and 2007-2009.

“It is not uncommon for La Nina to occur back to back,” he said. “Last summer we had a La Nina-like pattern pretty well established, so it was only a matter of time before it was officially declared.”

He added that other climate drivers, including a strong polar vortex over Antarctica earlier this year and a negative Indian Ocean dipole, were worsening wet weather conditions over eastern Australia.

The six wettest winter-spring periods on record for eastern Australia occurred during La Nina years. Across eastern Australia, the average December-March rainfall during La Nina years is 20 per cent higher than the long-term average.

The presence of La Nina also increases the chance of widespread flooding. Of the 18 La Nina events since 1900, 12 have resulted in floods across Australia. Parts of the country are likely to see an increase in tropical cyclones

University of NSW’s Climate Change Research Centre Associate Professor Andréa Taschetto said as climate change continues to alter the landscape, extreme La Nina and El Nino events are likely to become more common.

“In the future, we have more chances of storms, extreme rainfall and flood events,” she said. “It’s happening. We know global warming increases the chance of extreme events: bushfires, temperatures and droughts.”

The Bureau of Meteorology will provide their update at 1pm.

More to come

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