Heavy clouds hang over the Sydney Opera House and Sydney Harbour Bridge, in Sydney, Australia. (Photographer: Jack Atley/Bloomberg News)

La Nina Pattern Forms in Tropical Pacific Ocean, Australia Says

(Bloomberg) -- A weak La Nina weather pattern has formed in the Pacific Ocean, Australia’s weather bureau declared, and the event may bring wet weather to cropping and coal mining regions in the nation.

Climate models suggest this La Nina will be short-lived, persisting until early in the southern hemisphere autumn of next year, the Bureau of Meteorology said on its website. The central to eastern Tropical Pacific Ocean has cooled steadily since winter and has now reached La Nina thresholds.

La Ninas occur when the atmosphere above the equatorial Pacific reacts to cooling water temperatures and typically deliver colder winters across the northern U.S., drought in Brazil’s soybean-growing areas and flooding rains across the coal-mining regions of Australia. The U.S. last month said a weak La Nina formed in October and had a 64 percent chance of lasting through March.

Prices for agricultural commodities including corn, soybeans, wheat, cotton, sugar and coffee may rise and be volatile during a La Nina cycle, BMI Research said in October. Australia’s cotton output may benefit from La Nina rain, industry group Cotton Australia said in October, as the weather conditions can fill irrigation dams.

While La Nina events are typically associated with wetter than normal conditions across eastern and northern Australia, the sea surface temperatures in the current event aren’t typical of La Nina and so may result in a reduced likelihood of widespread, above average summer rain, the bureau said. La Ninas can also increase the chance of prolonged warm spells for southeast Australia, it said.

The last event was the 2010-2012 La Nina which included one of the strongest peaks on record. The nation activated a watch for the weather pattern in October this year with seven out of eight international climate models suggesting sea surface temperatures would reach La Nina levels by November.

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