Third La Nina set to smash east coast this summer, again

A La Nina event is set to smash Australia’s east coast this summer for the third year in a row.

The Bureau of Meteorology made the announcement on Tuesday and said recent cooling in the central tropical Pacific and model outlooks indicated that cooler-than-average ocean temperatures would be sustained until the end of the year.

A La Nina has been declared for this summer, making it the third year in a row the climate driver will smash the east coast.Credit: Wolter Peeters

The majority of models predict an easing of the La Nina early next year, which suggests a relatively short-lived event. BOM forecaster Jake Phillips said the event is likely to be weak to moderate.

The wet weather will linger throughout spring with the negative Indian Ocean Dipole (IOD) and the Southern Annular Mode compounding the wet weather across the country. Phillips said the three climate drivers interacting with one another doesn’t occur that often.

This is the first time on record that Australia has experienced three consecutive La Nina events coinciding with back-to-back negative IOD events. Australia has experienced 20 La Nina events since 1900 and 12 have coincided with flooding in eastern states. The average rainfall from December to March in La Nina years is 20 per cent higher than the long-term average.

The country has only experienced three back-to-back La Nina events three times since records began, Phillips said.

“Most of the time, we only get one La Nina year and then it swings back [to neutral],” he said. “In the eastern part of Australia, we should prepare for more rain than average in spring and the first half of summer.”

Australia was one of the last countries to declare the La Nina event, with international models showing the climate event had already begun earlier this year. This is because international weather agencies use different thresholds to measure La Nina. In Australia, the BOM measures sea surface temperatures over the Pacific Ocean around the country’s coastline.

This is the second year in a row of a negative IOD, which refers to the patterns of sea surface temperature. While positive dipoles are associated with dry weather, negative dipoles can bring heavy rainfall and flooding to parts of Australia.

The NSW SES said it is particularly concerned for the Hawkesbury, Nepean and Georges rivers, Northern Rivers, Mid North Coast, Central Coast and Shoalhaven catchment. The agency is preparing its units for future flooding events.

The agency has just experienced its biggest year on record. Between June 1 and August 3 this year, NSW SES members responded to 13,390 weather-related requests for assistance across NSW.

NSW SES Commissioner Carlene York said the third La Nina event presented a set of unique risks and challenges to the community, especially for those that had already undergone flooding events earlier this year.

Since the February and March floods, more than 1300 new members have undergone training, while more than 2077 applications are being assessed.

While La Nina causes warmer-than-average sea temperatures off Australia’s coast, which drive storms, it cools down ocean temperatures in the Northern Hemisphere, which creates drier onshore weather. The west coast of the US is experiencing its longest dry spell in 1200 years, while cities across the country’s west are grappling with how they manage dwindling water supplies.

In California, the statewide snowpack was just 38 per cent of the average as officials grow more concerned for the coming wildfire season.

Climate change continues to influence Australian and global climate. The country’s climate has warmed by 1.47 degrees between 1910 and 2020. In southern Australia, there has been a reduction of 10 to 20 per cent in the cool season rainfall, while in other parts of the country there has been a shift towards higher intensity rainfall over shorter periods of time.

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