The first El Niño phase of the Pacific Ocean in eight years is becoming more likely in 2023, increasing the odds of drier and warmer weather across eastern Australia.
While the Bureau of Meteorology's (BOM) Pacific status is currently set at El Niño Watch, defined as about a 50 per cent chance of development, one US federal government department says the true probability in recent weeks has risen closer to about 80 per cent.
The department also predicts it could be one of the strongest El Niño's in decades.
Pacific Ocean already showing shift to El Niño
The key developments this month include:
- A continued warming of the equatorial Pacific Ocean, especially off the west coast of South America where temperatures are now 5 degrees Celsius above average.
- A substantial tongue of sub-surface warm water below the tropical Pacific, often the precursor to further surface warming
- A weakening of trade winds over the eastern tropical Pacific
- A rapid strengthening of the El Niño signal from forecasting models
A rapid strengthening of the El Niño signal from forecasting models
This shift in the Pacific has already been picked up by the National Oceanic and Atmospheric Administration (NOAA) whose latest update points to "a 62 per cent chance of El Niño developing during May-July 2023".
NOAA's forecasters further increase the chance of El Niño to more than 80 per cent by spring, reflecting the high confidence the organisation has.
If El Niño does develop as expected the next question is its intensity.
According to NOAA there is a four in 10 chance El Niño will be 'strong' with ocean temperatures along the equator exceeding 1.5C above the baseline average, well above the BOM's El Niño threshold of 0.8C above average.
This would represent only the second 'strong' El Niño of the past 25 years.
What is El Niño and how does it affect Australia's weather?
El Niño is the name used to describe the warm phase of the Pacific when sea surface temperatures rise along the equator and trigger a change in global weather patterns.
For Australia, the main impact from El Niño is a shift in convection and cloud away from the western Pacific to the central and eastern Pacific, leading to a reduction in rain and increase in temperatures across northern and eastern parts of the country.
While El Niño increases the probability of drought in Australia during winter and spring, unlike its opposite La Niña, the impacts do not normally linger through summer, and this shorter period of influence can lead to exceptionally variable outcomes between events.
Indeed, Australia was left monthly unscathed from the last El Niño in 2015 despite it being one of the strongest on record, while a previous event in 2006 which was 'weak' led to record low rainfall in south-east Australia.
