A DRY weather event this season is slightly less likely in eastern Australia, according to the Bureau of Meteorology’s latest El Niño update.
The BoM said on Tuesday that five out of eight international climate models still indicate sea surface temperatures will exceed El Niño thresholds during the second half of 2017.
Last month seven of the major models indicated El Niño was on its way.
The likelihood of El Nino is still 50 per cent, or twice as likely as in an average year, BoM said.
Dale Grey, climate agronomist with Agriculture Victoria and author of The Break climate monitoring newsletter, said waters to the north of Australia remained warm at present which slows the development of an El Niño event.
“The Coral Sea is warm at present and remains a good source of moisture for eastern Australia.”
BoM supervisor of climate prediction services, Dr Andrew Watkins, said despite the downgrade, Australia remained on El Niño watch.
“It is still a good idea to have a plan for El Niño in your back pocket, for winter and spring,” Dr Watkins said.
And Mr Grey emphasised El Niño is not the only climate driver farmers needed to keep an eye on.
“The Indian Ocean Dipole (IOD) is a key driver of weather in many farming areas, especially in south-eastern Australia.”
The news is ominous on this front.
Mr Grey said there were early signs an IOD positive event, consistent with drier than average conditions, could potentially occur this year.
Correlation with IOD positive events and low rainfall in winter and spring through South Australia, Victoria and southern NSW has been very consistent, with the last 12 IOD+ events resulting in below average rainfall in these regions.
Mr Grey said climate drivers were emerging in the Indian Ocean at present.
“In the Indian Ocean, warmer water off Kenya, reversed trade winds near Sumatra and further movement of a body of cooler water at depth towards Indonesia, is the first evidence that a +IOD can potentially happen,” he said.
The BoM El Niño estimate is consistent with climate models run by the U.S and Japan, which along with Australia are the two other countries that are focused on the western Pacific Ocean, say the chance of an El Niño is 50-55pc and 50pc, respectively.
Dr Watkins said recent rainfall patterns across the country were indicative of times when “when El Niño is making up its mind about when it will happen”.
In March Gladstone had record rainfall of more than 600mm, the equivalent of Melbourne’s annual precipitation. The following month Gladstone achieved another record when it recorded no rain at all.
Perth too had no rain in April, while western NSW and Queensland have been dry, but Victoria “still getting OK rain”, Dr Watkins said.
“That is what can happen when there are signals of an El Niño. It doesn’t guarantee an event, but some regions may be drier, while other remain normal.”
El Niños typically bring eastern and northern Australia lower rainfall, higher daytime temperatures, more clear nights and increased frost risk, fewer tropical cyclones and a higher fire danger in the south east.
The event forms when the Pacific Ocean weather cycle that drives the easterly trade winds breaks down. This occurs when the eastern Pacific, along the west coast of south America, heats up and winds that usually blow cooling surface water from the chilly Peruvian coastline don’t pack their usual punch.
Mr Grey said the location of the El Niño event, rather than its intensity, was generally the key driver on its impact in Australia.
“When the Pacific Ocean is warm around the International Date Line is when we can see major influence on Australian weather.
“Further towards South America it is not so influential and further towards Fiji it gets too close to areas like the Coral Sea, meaning they do not cool off and hold their moisture.”
