Victorians could be in for a wet and warm end to 2020

Signs point to a wet October

Weather
Pacific Ocean conditions are feeding into forecasts of a wet few months in the lead-up to Christmas.

Pacific Ocean conditions are feeding into forecasts of a wet few months in the lead-up to Christmas.

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Signs point to a wet October to December period for northern parts and into the West Gippsland.

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Rainfall over last weekend was focused on the south west and central southern parts of Victoria.

It is likely we will see more rainfall this coming weekend, with a significant weather system expected to develop across central Australia and potentially impact parts of the state.

The last week of September is also likely to be wetter than average for northern Victoria.

Looking further ahead, most of the inland eastern two thirds of Australia, including northern Victoria, has high chances - of greater than 80 per cent - of a wetter than usual October.

At the same time, there is no strong push towards warmer or cooler than average days for most of the state. But nights are likely to be warmer than average.

The three-month outlook for October to December is showing high chances of above average rainfall for northern Victoria, extending through the centre and into West Gippsland.

The high chances also cover most of New South Wales, away from the coast, and most of the western half of South Australia.

Days are likely to be warmer than usual along Victoria's coast, and there are high chances that nights will be warmer than usual right across the state.

Broader climate drivers are lining-up and pointing to a wet end to the year.

There are signs the Pacific is on the verge of La Nina, including: cooling sea surface temperatures in the central Pacific; a lack of cloud around the date line; increasing pressure difference between the central and western Pacific; and stronger trade winds at times over recent months.

Most climate models predict the Indian Ocean Dipole (IOD) index will be negative during October, and for some of November too.

The IOD index has just returned to neutral values after spending several weeks in the negative IOD range.

We will have to wait and see if the index drops again, and if the sea surface temperature pattern - relatively warm waters off north west Australia - persists long enough to trigger a significant reaction from the atmosphere.

Both La Nina and negative IOD events typically increase the likelihood of above average rainfall for Victoria during spring.

And La Nina tends to favour a positive Southern Annular Mode (SAM) during spring to summer months, which typically enhances the wet signal of La Nina over south-eastern Australia.

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