Recent headlines predicting the emergence of El Nino in 2023 may be premature, given that the major short-term weather threat to most of Australia remains rain and flooding.
La Nina, the Pacific cool phase, was beginning to fade in December as sea surface temperatures (SSTs) rose by a fraction of a degree, but the warming trend has since stalled.
More importantly, the recent deterioration of the SST signal did not correspond to a change in atmospheric circulation over the Pacific.
Ongoing flood threat to most of Australia
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The weather has shown no signs of breaking free from the La Nina state it has been trapped in for nearly three years, as per ABC News.
This lag between the ocean and atmosphere is to be expected in a coupled system with positive feedback, which is why rainfall often remains above average after a La Nina has ended.
While strength oscillations are common and transitions are far from linear, the consensus is that La Nina has most likely peaked and is now in a slow retreat, with a return to a neutral Pacific expected within the next month or two.
La Nina increases the amount of moisture available for weather systems passing over eastern Australia to turn into rain, but its demise will not immediately end the flood threat due to the lag between changes in the ocean and atmosphere, especially given that the Pacific is not the only driver of Australia's weather patterns.
The Southern Ocean is also in a wet phase known as a positive SAM, which increases rainfall over eastern Australia.
This, combined with the final sting of La Nina, could support above-average rainfall in the coming months.
Weather whiplash for eastern states
The eastern states of Australia are reeling from weather whiplash, with Queensland breaking rain records and Sydney reaching temperatures not seen in nearly a year.
Today, the temperature in Sydney is expected to reach 30 degrees Celsius for the first time in nearly 340 days, breaking a 140-year-old record, as per 9News.
The western suburbs will be hotter, with Penrith expecting 37C and Parramatta expecting 33 degrees Celsius.
A cool change is expected later in the day, with rain in southern NSW.
It comes on the heels of a heat wave in Melbourne yesterday, when temperatures on the court reached 37 degrees.
Rain squalls hampered play even more, leaving organizers with a backlog of matches to complete - but more showers are expected today.
Meanwhile, parts of Queensland have been submerged by up to a metre of rain in a matter of days.
Conditions improved overnight in the state's north and central regions, but 13 flood warnings remain in effect.
During the recent weather event, roads were cut and bridges were flooded, leaving some people cut off from the rest of the country for days.
In the Mackay region, Finch Hatton received a metre of rain in just five days, while Proserpine received 800mm in a week.
Since 9 a.m. yesterday, Hamilton Island has received 113mm of rain.
The short answer is that it is too early to predict which phase the Pacific will enter, but a fourth La Nina cannot be ruled out.
Not only would four in a row be historically unprecedented, but a growing band of heat beneath the surface does not bode well for the return of La Nina.
The last full-fledged El Nino occurred eight years ago, and it was responsible for the warmest year on record on Earth.
Several recent model forecasts have indicated a rapid shift to El Nino this year, with NOAA estimating the risk to be as high as 50% by August, but early predictions should be used with caution as model accuracy is generally low at this time of year.
Model accuracy improves when the Pacific enters a cool or warm phase, which usually occurs around winter.
El Nino increases the likelihood of drought and high temperatures in Australia's eastern states during winter and spring.
