EXPLAINED: What the La Niña Alert means for region
This week the Bureau of Meteorology raised its El Niño-Southern Oscillation Outlook to La Niña Alert status, meaning the chance of a La Niña occurring this year has increased to 70 per cent, roughly three times the normal likelihood.
The Bureau’s manager of climate operations, Dr Andrew Watkins, said La Niña typically results in above-average winter-spring rainfall for Australia, particularly across eastern, central and northern regions.
According to BoM, the last significant La Niña event was in 2010-11, which was the Australia’s wettest two-year period on record beating the previous record from the La Niña years of 1973-74.
The last time the Pacific Ocean approached La Nina conditions was in late 2017, but thresholds were only briefly exceeded.
Climatologist Greg Browning told the NewsMail the current event is currently well below the strength of either of the earlier events (for the same time of year), particularly the 2010/11 event.
“That is not to say that the current conditions will not strengthen rapidly in the coming months, although the forecast guidance we use suggests it is unlikely to get close to the strength of the earlier events,” he said.
“Even with a weaker La Niña, the chance of widespread and prolonged heavy rainfall and flooding is greater than in an average year.”
In August 2010 Bundaberg recorded a record 126mm but it was “unlikely” those totals would be seen this month.
“The development of the current La Niña Has ben slower than in 2010, so the atmosphere is currently not as likely to lead to high rainfall totals at this stage of the year,” Mr Browning said.
“That August rainfall total from 2010 is unlikely to be reached, however there is a greater than 80 per cent chance of above average rain across nearly all of southern Queensland, including all of the Wide Bay & Burnett District, in spring.
“It is impossible to give forecasts of actual rainfall amounts, but as the median rainfall for Bundaberg is 183mm during spring, it is highly probable the total will be greater than this.”
From Sunday, BoM has forecast single digit minimum temperatures for Bundaberg.
Mr Browning said daytime temperatures were significantly influenced by the presence of cloud/rainfall.
“So, with the current rainfall forecasts indicating a high chance of above average, there is likely to be more cloud than usual,” he said.
Dr Watkins said La Nina typically also brings cooler and cloudier days, more tropical cyclones, and an earlier onset of the first rains of the wet season across the north.
“The cooling of surface temperatures in the tropical Pacific Ocean and an increase in the strength of the Pacific Trade Winds indicates the chance of La Niña has risen,” Dr Watkins said.
“When these two changes occur at the same time, at this time of year, we see a greatly increased chance of a La Niña forming and persisting through spring.
“Climate models suggest that further ocean cooling and intensification of Trade Winds may occur over the coming months, which has triggered the Bureau to shift from a La Niña Watch, issued on 26 June, to a La Niña Alert.”
The Bureau will continue monitoring the situation closely.
For more information on La Niña and the impacts of past events, head to the Bureau’s ENSO Outlook page.