US climate agency declares chance of El Niño now above 90 per cent in 2023

Eastern Australia is facing the increased likelihood of a dry winter and spring with a United States federal agency declaring an El Niño pattern almost a foregone conclusion.

The US Climate Prediction Centre (CPC) has raised the chance of El Niño, the Pacific warm phase, to above 90 per cent by August and indicated a greater than 50 per cent chance of a "strong" event by late in the year.

A "strong" El Niño is when Pacific Ocean water temperatures climb more than 1.5 degrees Celsius above average and has only occurred once previously in the past 25 years.

Pacific edges closer to El Niño

While the Pacific Ocean has been transitioning towards El Niño for months, the overlying weather across the Pacific Basin has so far remained unresponsive.

"While the warming near coastal South America remains striking, the basin-wide coupled ocean-atmosphere system remained consistent with ENSO-neutral," the National Oceanic and Atmospheric Administration [NOAA] stated in its May update.

This coupling between the ocean and atmosphere is a critical step for establishing ENSO events (El Niño or La Niña), as the reciprocal reinforcement allows for a prolonged shift in global weather patterns for up to a year.

Despite the lack of compliance between the ocean and weather this Autumn, the increased confidence of an El Niño is due to a continued warming of the equatorial Pacific along with a predicted burst of westerly winds, which could send the Pacific beyond the point of no return.

"The combination of a forecasted third westerly wind event in mid-late May, and high levels of above-average oceanic heat content, means that a potentially significant El Niño is on the horizon," stated the CPC.

The Australian Bureau of Meteorology (BOM) agrees this burst of westerlies could be the tipping point, suggested by their recent reference to a Madden-Julian Oscillation (MJO), a fluctuation of tropical weather, easing easterly trade winds.

"An MJO pulse over the western Pacific would likely weaken trade winds across the equatorial Pacific Ocean," the BOM said.

"This, in turn, would result in further warming of the equatorial Pacific Ocean and hence drive further development towards El Niño."

Rain and temperature forecasts show clear El Niño signal

If El Niño develops as expected the consequence will be a change in weather patterns across the globe.

Typical impacts for Australia are notable through winter and spring across roughly the eastern half of the country and include:

• A reduction in rain, most pronounced over inland regions
• Warmer average maximum temperatures, apart from over north Queensland
• An increase in the frequency and intensity of extreme hot days
• An increase in winter frost over south-east states
• A decrease in winter snowfall
• Later monsoon onset and fewer tropical cyclones
• Heightened risk of bushfires, particularly over south-east states

While the list of impacts may seem concerning, no two El Niño's are equal and the strength of an event is not proportional to the impact, particularly in Australia where other drivers, like the Indian Ocean, can enhance or negate the Pacific influence.

Occasionally even during the strongest El Niño's, like in 2015 and 1997, another climate driver can step in and reduce the effect for a portion of the event.

What's concerning this year is modelling currently favours a dry signal from the Indian Ocean which will reinforce El Niño, and that combination in the past has led to some of eastern Australia's driest years on record, including 1982, 1994 and 2006.

It's too early to make any doomsday predictions for 2023, however long range forecasts have already picked up on this double dry driver, including the BOM's seasonal model which favours below average rain across most of Australia this winter.

Story by Tom Sanders

Original link here https://www.abc.net.au/news/2023-05-14/chance-of-2023-el-ni%C3%B1o-australia-now-above-90-per-cent/102340672