Australia has been placed on La Niña watch by the Bureau of Meteorology with early signs the climate pattern linked to cooler and wetter conditions across most of the country could form later this year.
The bureau said there was now a 50/50 chance of La Niña forming this year with sea surface temperatures in the tropical Pacific steadily cooling since December.
But the bureau stressed that record high global sea surface temperatures seen between April 2023 and April 2024 meant that past experiences of how conditions in the Pacific could change “may not be reliable”.
Australia’s summers of 2020, 2021 and 2022 were all influenced by La Niña in a rare “triple dip” event, before the system – known as the El Niño Southern Oscillation (ENSO) – flipped to the generally warmer and drier El Niño phase last summer.
The US government’s National Oceanic and Atmospheric Administration last week put the chance of a La Niña developing between July and September at 69%.
“Moving to La Niña watch does not mean that the bureau is declaring that a La Niña event is under way,” the bureau said.
Bureau climate manager Dr Karl Braganza stressed the bureau’s long-range forecasts were not dependent on the state of the ENSO cycle.
“The best guidance for future rainfall or temperature forecasts is the bureau’s long-range forecast,” he said.
“The long-range forecast for June to August is showing an increased chance of above average rainfall for parts of eastern Australia, and parts of Western Australia and South Australia.
“There are roughly equal chances of above or below median rainfall for most of eastern Australia, including much of Queensland, New South Wales, Victoria and Tasmania.”
The current long-range forecast, which will be updated at the end of this month, shows that maximum and minimum temperatures are likely to be warmer than usual across the entire country.
The Bureau of Meteorology has moved to a La Niña Watch.
— Bureau of Meteorology, Australia (@BOM_au) May 14, 2024
While conditions in the tropical Pacific Ocean are currently neutral, there are some signs that a La Niña may form in the Pacific Ocean later in 2024.
Details: https://t.co/0mjJWBCKzd pic.twitter.com/7qhdarANPI
Three of the seven climate models surveyed by the bureau, which includes its own, suggest the Pacific will enter La Niña territory by September.
Another climate “driver” that can influence Australia’s weather – known as the Indian Ocean Dipole (IOD) – had been heading towards a positive phase that can see less rainfall and higher temperatures in winter and spring.
But after seven weeks of being in positive territory the development of a positive IOD, which requires thresholds to be met for eight weeks, may now have stalled, the bureau said.
While the bureau’s modelling suggested positive IOD conditions could still develop, the latest forecasts were suggesting a weaker event.
“At this time of year, historical skill of IOD forecasts beyond autumn is low,” the bureau said.
