Rainfall over last weekend was focused over the south-west and central southern parts of Victoria. And it's likely we will see more rainfall this coming weekend, with a significant weather system expected to develop across central Australia, potentially impacting parts of the state.
The last week of September is 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 (greater than 80%) of a wetter than normal 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.
October rainfall outlook
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 NSW away from the coast and most of the western half of SA. Days are likely to be warmer than usual along Victoria's coast, and there are high chances nights will be warmer than usual right across the state.
Our broader climate drivers are lining up for a wet end to the year. There are signs the Pacific is on the verge of La Niña: 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 November too. The IOD index has just returned to neutral values after spending several weeks in the negative IOD range. We'll have to wait and see if the index drops again, and if the sea surface temperature pattern (relatively warm waters off northwest Australia) persists long enough to trigger a significant reaction from the atmosphere.
Both La Niña and negative IOD events typically increase the likelihood of above average rainfall for Victoria during spring. And La Niña tends to favour a positive Southern Annular Mode (SAM) during spring to summer months, which typically enhances the wet signal of La Niña over south-eastern Australia.