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Indicator tips toward wet weather outlook

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A negative Indian Ocean Dipole (IOD), one of the drivers of wetter weather in parts of Australia, is set to form this year potentially increasing the risk of floods and thunderstorms while also having implications for the bushfire season.

A negative IOD is declared when there have been at least eight weeks of readings below a certain threshold. Last week’s reading was slightly above the threshold, while it was below the key levels for the previous six weeks.

“Most climate models surveyed by the bureau predict the IOD to return to below the negative IOD threshold, with a negative IOD event likely for the second half of the southern hemisphere winter and into spring,” the Bureau of Meteorology said.

IAG Executive Manager Mark Leplastrier says a negative IOD means the increased potential for north-west cloud bands across Australia over the next six to nine months.

“Based on this and our study of a number of other weather indicators, this could result in better than average rain for inland areas, particularly cropping areas, but there could also be the increased risk of heavy rain, river flooding and thunderstorms for much of the continent,” he told insuranceNEWS.com.au.

“This also means it is likely we will have a reduced risk of early season bushfires for eastern and south-east Australia, and a normal situation for WA and Tasmania.”

A negative Indian Ocean Dipole, combined with a Pacific Ocean La Nina pattern, has been responsible in past years for significant rainfall and widespread flooding in Australia, including in 2010.

International models the Bureau of Meteorology surveys anticipate the El Nino-Southern Oscillation (ENSO) will remain neutral during winter, while two models forecast ocean temperatures reaching the La Nina threshold during September.

Recent wet weather has included the flooding and strong winds that particularly brought damage to parts of Gippsland and the Dandenongs in Victoria around June 9-11, causing the Insurance Council of Australia to declare a catastrophe.

Victoria had its wettest June since 2014 and many locations recorded their highest daily rainfall on record for the month, the bureau says.

The IOD and the ENSO reflect changes in tropical sea surface temperatures in the Indian and Pacific oceans.