Indian Ocean Dipole – Michmutters

Southern Queensland weather forecast for another wet spring

Authorities get ready

Authorities have also started preparations for a wet spring, with flooding in Queensland this year having already claimed more than 20 lives.

Dam operator Sunwater said 11 of its 19 reservoirs across Queensland were either at or close to capacity.

A lot of water rushes over a dam spillway

Leslie Dam at Warwick is one of the 11 dams at full capacity.(Supplied: Chris McFerran)

Sunwater executive general manager of operations, Colin Bendall, said communities needed to be vigilant if more early spring or summer rain was coming.

“Some of the preparation we’ve been doing is we conduct exercises with the local disaster management groups, and the Bureau of Meteorology,” Mr Bendall said.

He said staff were also being trained in the use of emergency action plans in the event of any further spills from dams.

wet-summer

University of Southern Queensland climatologist Chelsea Jarvis said there was between a 65 to 80 per cent chance regions such as the Darling Downs would exceed their median rainfall.

She said scientists would continue to monitor the situation to see whether the Indian Ocean Dipole strengthened towards the end of the year.

“The end of this Indian Ocean Dipole event, whether it be October or December, can also determine how the likelihood of rain going into summer,” Ms Jarvis said.

“The second thing I’d be looking out for is what’s going on in the Pacific Ocean with this La Nina event, it’s just sort of hanging out there.”

Higher chance of more tropical cyclones, early monsoon amid negative Indian Ocean Dipole and possible La Nina

Northern Australia’s wet season is likely to arrive earlier this year, according to the Bureau of Meteorology (BOM), bringing with it a higher likelihood of more tropical cyclones off coasts.

Much of south-eastern Australia has been impacted by record-breaking floods as a result of La Nina, while the north of the continent recorded decent rainfall totals during the last wet season.

Now the weather bureau has officially declared another climatic phenomenon — known as the negative Indian Ocean Dipole — that’s expected to add to recent unrelenting rain on the east coast.

The weather system is also predicted to lead to wetter weather across the Top End of the Northern Territory and Far North Queensland. However, parts of northern Western Australia are likely to remain somewhat drier.

A map of the northern half of Australia, with parts of the NT and Qld showing an early rainfall onset. — The Bureau of Meteorology is forecasting vast parts of northern Australia will see an early onset of rainfall, but a later onset in WA is possible.(Supplied)

Northern Australia’s wet season typically runs from December to April, following a build up of hot and humid conditions from October.

The weather bureau measures how early or late the rainfall onset is by how long it takes for rain gauges to record 50mm after the start of September. Typically, gauges hit the 50mm threshold in Darwin in late October.

“There is a high chance of getting to 50mm from the 1st of September potentially by early October or maybe even late September,” the BOM’s senior forecast Moses Raico said of this year’s conditions.

The culprits are vast climate drivers across the Pacific and Indian Oceans, including the La Nina, responsible for much of the east coast’s wet weather so far this year.

The BOM is predicting a 50:50 chance of La Nina forming for a third straight summer, however Mr Raico said it was actually a negative Indian Ocean Dipole that was more likely to influence rainfall in northern Australia.

He said this was when “waters across the eastern side of the [Indian Ocean] basin are warmer than compared to what’s over on the western side.”

“The combination of those warmer waters, and if we also get La Nina called later on, it could help contribute to seeing wetter conditions than what we’d expect, which would contribute to a greater chance of a rainfall thresholds being met.”

While every year is different, the areas shaded in green usually receive wetter than normal weather during a negative Indian Ocean Dipole – particularly the south-east of Australia.(ABC: Shakira Wilson)

Earlier rain, more potential cyclones

Each year, the monsoon arrives at roughly the same time. In Darwin, drenching rains typically begin between Christmas and New Years.

But Mr Raico said the combination of a La Nina and a negative Indian Ocean Dipole could bring the monsoons forward to sometime earlier in December.

“The exact timing though, it’s a bit hard to actually pin point,” he said.

“Definitely, if that were to take place and we do see those warmer sea surface temperatures, then that generally would play out with potentially greater than average tropical cyclones in the season.”

Typically, a negative Indian Ocean Dipole and La Nina triggers higher than average rainfall across northern Australia during its wet season.

But the BOM, in its report wrapping up the 2021-22 wet season, acknowledges this wasn’t entirely true.

“The 2021–22 La Nina was conducive to the early start to the wet season and above average rainfall until January 2022,” the BOM said.

“However, somewhat atypically for a La Nina, many areas of northern Australia were drier than average from February to April 2022.”

Michael O’Brien says the forecast will benefit prawn fishers. (ABC News: Dane Hirst)

Rainfall good news for some

Increased wet weather might bring to a premature end the Northern Territory’s bumper tourism season, which runs through the dry.

But those likely to benefit include prawn fishers, whose benefits greatly from rainy conditions.

Australia Bay Seafoods general manager Michael O’Brien said 16 boats had already gone out into the Gulf of Carpentaria in the past week for the tiger prawn season.

“[The forecast] is great news for us because our banana [prawn] season, which is the first half of the year, is totally related to the amount of rain we get to flush the rivers out,” he said.

Mr O’Brien said rains flushed “the rivers out with all the smaller prawns so they can go out and grow”.

“Our prawns will be bigger, which is good for everybody – good for the market, good for us and good for the consumer that’s going to eat big prawns.”

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