Recent headlines warning of El Niño's emergence in 2023 could be premature considering the major short-term weather threat to most of Australia is still rain and flooding.
The flood risk is especially high for Queensland and eastern NSW during the coming months, as La Niña and other rain-producing climate drivers coincide with the eastern seaboard's wettest time of year.
La Niña, the Pacific cool phase, was showing signs of decaying in December as sea surface temperatures (SSTs) rose by a fraction of a degree, however the warming trend stalled during the past two weeks.
More importantly, the recent weakening of the SST signal did not coincide with a change in the atmospheric circulation over the Pacific.
In other words, the weather has shown no indication of breaking free from the La Niña state it's been trapped in nearly continuously for three years.
This lag between the ocean and atmosphere is expected in a coupled system where positive feedbacks are present and is why rainfall often remains above average immediately after a La Niña has concluded.
While oscillations in strength are typical and transitions are far from linear, the consensus is La Niña has most likely peaked and has now commenced a slow retreat with a return to a neutral Pacific imminent at some point during the coming month or two.
Cool anomalies across the equatorial Pacific have eased during the past 30 days signalling La Niña has commenced weakening, according to the National Oceanic and Atmospheric Administration (NOAA).
Queensland and NSW enter flood months For Queensland and eastern NSW January to March are the wettest months of the year although the coastal strip can remain exceptionally wet into early winter due to East Coast Lows.
The timing of Hawkesbury River floods is a prime example.
All but five of the 46 ten metre floods at Windsor since 1799 occurred in the period from February to August and surprisingly there has never been a 10 metre flood in December or January.
For Queensland, as is evident this week, the peak flood period starts a little earlier in January.
La Niña increases the amount of moisture available for weather systems passing over eastern Australia to turn into rain, however due to the lag between changes in the ocean and atmosphere its demise will not immediately end the flood threat, especially considering the Pacific is not the only driver of Australia's weather patterns.
The Southern Ocean is also currently in a wet phase called a positive SAM that enhances rainfall over eastern Australia.
This combined with the final sting of La Niña could be sufficient to support above-average rain during the coming months.
Will El Niño return in 2023? The short answer is, it's too early to say for certain what phase the Pacific will enter, but we can rule out a fourth La Niña.
Not only would four in a row be historically unprecedented but a growing band of heat below the surface is not conducive for La Niña 's return.
What remains is either El Niño, the Pacific warm phase, or neutral.
The last fully fledged El Niño was eight years ago and was responsible for Earth's warmest year on record.
Several recent model forecasts have indicated a rapid shift to El Niño this year and NOAA estimates the risk is as high as 50 per cent by August, however early predictions should be used with caution as model accuracy is generally low at this time of year.
Once the Pacific begins a transition into a cool or warm phase, normally around winter, model accuracy increases.
For Australia, El Niño increases the likelihood of drought and high temperatures through winter and spring across eastern states.
A neutral Pacific would therefore be the preferred outcome this year, although the prolonged record dry spell from 2017 to 2019 and the Black Summer bushfires which followed occurred without a fully-fledged El Niño.
That indicates the background influence of climate change along with other climate drivers are more than capable of bringing extreme heat and drought to Australia.
Story by: ABC meteorologist Tom Saunders
Original story link: https://www.abc.net.au/news/2023-01-18/la-nina-weakens-el-nino-weather-pattern-predictions/101865396
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