There is a negative Indian Ocean Dipole (IOD) event underway, and a wet outlook is set to continue, according to the Bureau of Meteorology (BoM).
A negative IOD typically increases the chance of winter and spring rainfall over much of southern and eastern Australia, along with warmer days than usual in northern Australia.
The IOD describes a natural climate cycle brought about by sustained changes in the difference between sea surface temperatures of the tropical western and eastern Indian Ocean.
The Bureau of Meteorology’s head of long-range forecasting Dr Andrew Watkins, said that the Bureau’s 3-month climate outlook is for above average rainfall for much of Australia, particularly for the central and eastern states.
“With wet soils, high rivers and full dams, and the outlook for above average rainfall, elevated flood risk remains for eastern Australia,” he explained.
There is a high chance (greater than 80 per cent) of above median August to October rainfall for much of the eastern two-thirds of the mainland, with chances reducing gradually in the west, and tending to below median for western Tasmania and an area of south-western WA, the BoM’s Climate Outlook for August to November 2022 says.
“Most of the eastern two-thirds of the mainland has more than double the normal chance of unusually high rainfall (in the wettest 20 per cent of all August–October periods over 1981–2018) rising to over triple the normal chance for parts of the tropics and scattered parts of the south-east,” the report explained.
“It should be noted that May to September is the northern Australian dry season. This means most of tropical northern Australia typically has very low rainfall totals during this time (large areas less than 25 mm for the season), and only a small amount of rainfall is needed to exceed the median.”
August to October maximum temperatures are likely to be above median across the tropics and parts of western and southern Australia, but below median for parts of the east and southern interior, according to the report.
“August to October maximum temperatures are likely to be above median across the tropics, south-eastern SA, most of Victoria, all of Tasmania, and most of WA away from the south-eastern interior. Below median maximum temperatures are likely for the south-eastern quarter of Queensland and most of central-eastern and north-eastern NSW, extending across inland South Australia into south-east WA (chance of exceeding the median is less than 40 per cent),” the report stated.
“There is more than double the normal chance of unusually high maximum temperatures (in the warmest 20 per cent of all August to October periods over 1981–2018) across most of the tropics, and Tasmania.
“Minimum temperatures for August to October are very likely to be above median almost Australia wide, with a greater than 80 per cent chance for most parts.
“There is an increased chance of unusually high minimum temperatures (in the warmest 20 per cent of all August to October periods over 1981–2018) for August to October across almost all of Australia, ranging from 1.5 times the normal chance for south-western WA, to greater than three times the normal chance across most of the east, and more than 4 times the normal chance for parts of the tropics.
The report said emerging negative Indian Ocean Dipole event, along with warmer than average waters around northern Australia, and a neutral to cool phase of the El Niño–Southern Oscillation, are likely to be influencing this outlook.
“The emerging negative Indian Ocean Dipole (IOD) event outlooks indicate negative IOD conditions are likely for the coming months. A negative IOD increases the chances of above average winter–spring rainfall for large parts of Australia. It also increases the chances of warmer days and nights for northern Australia,” the report revealed.
“Above average sea-surface temperatures, particularly to the north of Australia are likely to be contributing to the wetter outlooks and warmer nights forecast for many areas.
“The ENSO Outlook is at La Niña WATCH, meaning around a 50 per cent chance of La Niña reforming later in 2022. Three of the seven models are suggesting La Niña could return by early spring, with a fourth in late spring. The remainder predict a neutral ENSO phase until the end of 2022. La Niña increases the chances of above average rainfall for much of northern and eastern Australia.
“The Southern Annular Mode (SAM) is likely to remain neutral to positive over the coming four weeks. A neutral SAM has little influence on Australian climate, while a positive SAM in winter typically increases the chance of below-average rainfall to the far south-west and parts of the south-east.
Australia’s temperature and rainfall variability are also influenced by global warming caused by human activities. Australia’s climate has warmed by around 1.47 °C for the 1910–2020 period. Southern Australia has seen a reduction of 10 per cent to 20 per cent in cool season (April–October) rainfall in recent decades. There has also been a trend towards a greater proportion of rainfall from high intensity short duration rainfall events, especially across northern Australia.”
Communities are encouraged to keep up to date with the latest Bureau forecasts and warnings through the Bureau’s website and BoM Weather app and follow the advice of emergency services.