If you’re sick of all the rain, you may want to look away.
Large parts of the nation are increasingly assured to get wetter than average conditions in the months ahead as a climate driver that typically brings more rain to large parts of eastern and southern Australia is set to officially be declared today.
It’s known as a negative Indian Ocean Dipole (IOD), which reflects changes in sea surface temperatures across the tropical Indian Ocean that subsequently impact Australia’s weather, and is associated with producing moisture-laden air and more rain.
The IOD index is a measure of sea surface temperatures across the Indian Ocean. A negative IOD occurs when water on the eastern side near Indonesia is warmer than average and the west is cooler than average.
Since late July, the index has been below the threshold to be considered negative – less than or equal to −0.4 °C. (And in the BoM’s latest update the value was well below that at −1.27 °C).
That has now been the case for eight weeks – hitting a benchmark that global weather agencies, such as the Bureau of Meteorology, use to officially declare the climate driver.
“It’s just to make sure it’s sustained enough to be an actual event, not just a short two or three week signal that dies out,” Weatherzone meteorologist Ben Domensino told Yahoo News on Tuesday.
As a result, the BoM will officially declare a negative IOD today.
“It’s been strong enough and sustained for long enough that it is able to be declared based on the Bureau’s definition,” he explained.
Negative IOD weather event boosts confidence in wet outlook
When the requisite conditions of a negative IOD have been in place, they influence moisture levels and affect circulation in the atmosphere, raising the probability of supercharged bouts of rain.
Speaking to Yahoo News last month, Dr Andrew Watkins, the former head of long-range forecasts at the BoM, said a declaration of a negative IOD would really solidify the Bureau’s long-term outlook which has been predicting wetter than average conditions and warmer than average nights for spring.
“What gives us a bit more confidence that will occur is that negative IOD … That’ll give us real confidence in that outlook if the negative IOD kicks in,” he said.
Overall, scientists know less about the Indian Ocean Dipole than the La Niña and El Niño climate drivers. Source: Getty/BoM
While residents in Sydney might not be stoked at the prospect of more rain, plenty of farmers in South Australia and Victoria will be happy to see the heavens continue to open up, with Dr Watkins hoping those struggling in the states will be able to “turn the corner” in the weeks ahead.
The Bureau of Meteorology currently predicts the weather event will continue for spring before the index returns to neutral in early summer.
Dr Watkins said last month the climate driver doesn’t “doesn’t point towards” previous flooding events such as those seen in 2022 when the last confirmed negative IOD contributed to wild weather in southeast Queensland, NSW, Victoria and Tasmania.
“It’s not a signal for another really bad, severe weather season later in the year,” he said. However, if the soil is soaked and a severe weather event does occur, “there’s not much place for the water to go,” he noted.
How will the weather event impact Australia?
The expectation of soggy conditions will be felt by the millions of residents in eastern, central and southern parts of the country.
October is expected to bring the strongest signal for wet weather, with the chance of unusually heavy downpours ranking in the top 20 per cent of spring totals historically.
From September to November, northern Australia will transition from the dry to the wet season, bringing increased humidity, storms, and showers. In contrast, parts of southern Western Australia are likely to remain drier than usual.
At the same time, temperatures are projected to climb above average almost everywhere except for southern WA.
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