Reuters — Australia’s weather bureau is not convinced that a La Nina weather pattern is forming that could change rainfall patterns and bring wilder weather to parts of the Americas, Asia and Oceania, affecting crop production, a senior climatologist said.
Why it matters: La Nina or El Nino weather patterns influence the jet stream, which affects temperatures and precipitation in North America.
La Nina, and its analogue, El Nino, are caused by the cooling or warming of ocean surface temperatures in the eastern and central Pacific.
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The former typically brings greater rainfall to eastern Australia, Southeast Asia and India with drier weather in the Americas, while El Nino does the reverse. Both can also lead to hurricanes and flooding.
Models forecasting the weather patterns typically converge on a strong signal around this time of year but there is currently a lot of variation, said Felicity Gamble of Australia’s Bureau of Meteorology.
“That speaks to the fact that there’s still a lot of uncertainty in the system,” she added.
La Nina conditions were present in weak strength, and would probably persist through December, the U.S. National Oceanic and Atmospheric Administration (NOAA) said this month.
The Australian bureau’s model shows sea surface temperatures brushing a La Nina threshold of 0.8 degrees Celsius below neutral levels in October, November and December before moving back towards neutral.
But the effect of the cooler water on atmospheric indicators such as cloud patterns and trade winds is not strong enough to impart confidence that a La Nina is taking place, Gamble added.
“Our model is probably one of the weaker forecasts for La Nina,” the senior climatologist said.
Although NOAA considered the atmospheric response sufficient, she said, “We’d like to see more.”
Except for some islands in the southwest Pacific, there was also no strong signal of rainfall patterns typically associated with La Nina, Gamble added.
“Because we aren’t seeing a particularly dominant La Nina-like pattern, we aren’t seeing the same magnitude of impacts … When you have a weaker signal, you can have other influences start to play a bigger role and perhaps override it,” she said.
Three consecutive La Nina events between 2020 and 2023 brought plentiful rainfall leading to record crop yields in Australia, but drought and heatwaves in parts of the Americas.
— Reporting by Peter Hobson
