The world’s meteorologists and climate experts are watching closely for another burst of westerly winds across the Pacific that could trigger the first El Nino weather pattern since 2009-2010.
“Basically it is primed for a strong El Nino, but it needs the final push,” said Axel Timmermann, the professor of oceanography at the international Pacific research centre, University of Hawaii. “This is perhaps the most-watched El Nino of all time.”
The weather watch comes as winter remains largely at bay for much of Australia. Sydney and Melbourne broke heat records during autumn and maximums in both cities have been about 2-3 degrees above average for June.
This week, Sydney can expect tops most days of 20-22 degrees, or about 3-5 degrees above normal, while Melbourne's maximums will be 1-2 degrees above the June average of 14 degrees, the Bureau of Meteorology said.
An El Nino could make this year another warm one for Australia. Last year was the country's warmest in more than a century of records.
El Ninos form when waters in the eastern Pacific turn unusually warm compared with the west, stalling or reversing the easterly trade winds. The pattern is a major driver of the world’s climate and can trigger droughts and bushfires in Australia and east Asia, while bringing heavy rains to countries bordering the eastern Pacific.
Drought conditions in Australia are more likely if an El Nino is coupled with conditions in the Indian Ocean that lead to less moisture streaming in across the continent from the north-west. Known as a positive Indian Ocean Dipole, those conditions have backed off slightly in the past fortnight, the Bureau of Meteorology said in its latest El Nino update, released on Tuesday.
70 per cent-plus chance
For now, the likelihood of an El Nino remains at least 70 per cent. Confirmation, though, may slip back to spring rather than late winter as had been predicted earlier, the bureau’s head of climate prediction services, Andrew Watkins, said.
“The odds of having a very strong event have probably eased somewhat [from readings in April and May]", he said. “But it can’t be ruled out.”
A strong El Nino does not necessarily result in extreme conditions in Australia. For instance, the “super El Nino” in 1997-98, the largest such event in the 20th century which set then-global temperature records, did not result in Australia suffering a severe drought.
Australia is already experiencing El Nino-like conditions, with the most recent three-month outlook from the Bureau of Meteorology indicating the odds favour a drier and warmer-than-average winter for most of the nation.
Conditions remain favourable for an El Nino event to develop, with sub-surface temperatures in the Pacific at depths of about 100 metres running about 5 degrees above normal. The patch of anomalously warm waters has also reached the far-eastern Pacific, Dr Watkins said. Surface temperatures are about 1-2 degrees above normal for much of the equatorial ocean.
“Right now, this is the crucial stage for the El Nino to gain amplitude,” Professor Timmermann said. “If the westerlies do not come along, it will be a weak to moderate El Nino.”
Dr Watkins said the focus was now on a strong pulse of cloud and rain in the equatorial Indian Ocean. That pulse – known as a Madden-Julian oscillation – may be the source of the next burst of westerly winds if it retains sufficient strength when it reaches the Pacific.
“We’re all waiting to see what happens,” Dr Watkins said.