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Floods warning as negative IOD declared, La Nina watch remains

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Australia’s east coast faces “elevated” flood risk in the coming months through to spring following the formal declaration of a negative Indian Ocean Dipole (IOD) event, the Bureau of Meteorology (BOM) says.

The BOM’s latest Climate Driver Update also maintained its “watch” notice for La Nina, meaning there is around a 50% chance of the “little girl” returning later this year, potentially creating above-average rainfall across northern and eastern parts of the country.

Previous BOM updates in the last few months have said a negative IOD event was likely this winter based on the readings from modelling.

“A negative IOD event is under way,” the Climate Driver Update released yesterday says. “The IOD index has been very close to or exceeded negative IOD thresholds, that is at or below -0.4 degrees Celsius over the past eight weeks.

“All climate model outlooks surveyed indicate that negative IOD conditions are likely to continue into late spring.”

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.

BOM Senior Climatologist Andrew Watkins says a negative IOD refers to a change in the temperature patterns out in the tropical Indian Ocean. What this means is there will be warmer conditions off Indonesia and cooler-than-normal conditions off Africa.

He says the weather patterns tend to follow where that warmer water is, shifting the wetter conditions towards Australia.

“Typically a negative [IOD] sees wetter than normal winter and spring conditions across southern and eastern Australia and we could also see warmer conditions across northern Australia as well,” Dr Watkins said.

“The rainfall outlook for the coming three months is for wetter-than-normal conditions across much of the eastern two-thirds of Australia.”

He says with soils still wet and dams still full from the heavy rainfall this year, the “flood risk remains elevated for eastern Australia” given the forecast for more soggy weather in the coming months.

The Climate Drive Update says three of seven climate models surveyed suggest La Nina could return in early southern hemisphere spring, with a fourth in late spring. The “little girl” has visited in the last two years, contributing to the heavy rainfall in NSW and Queensland.

In a news release this afternoon, the BOM says severe weather conditions continue across five states and territories.

Severe weather warnings for damaging winds and dangerous surf are currently in place for SA, Victoria, Tasmania, NSW and the ACT.

“Conditions will ease for some parts today and worsen on Wednesday night into Thursday morning, as a complex low pressure system moves towards the coast,” the BOM says.

“Heavy rainfall is expected in some regions, with isolated major flooding possible in catchments in southern NSW, northern Tasmania and north-east Victoria. Minor to moderate flooding is possible elsewhere in the affected areas.”