The US National Oceanic and Atmospheric Administration's Climate Prediction Centre yesterday confirmed the existence of a La Nina after a large mass of cool water that started forming along the equator was detected in the second half of last year. Typically, La Nina, the opposite of drought-inducing El Nino, also heralds unseasonal rain in much of Queensland and NSW.
In the US, La Nina brings warmer and drier conditions in southern California as temperatures in the eastern Pacific cool, and an intensified hurricane season in south-eastern states.
NASA climatologist William Patzert said he had watched the current La Nina strengthen over the past six months and expected its impact to be felt in Australia into winter.
"Over the next six months, everyone will have to be vigilant and plan accordingly," he said.