A wet outlook for the south-west is expected over Spring as the Bureau of Meteorology declared La Nina had developed in the Pacific Ocean.

La Nina typically results in above-average spring rainfall for Australia, particularly across eastern, central and northern regions.

It can also mean cooler days, more tropical cyclones, and an earlier onset of the first rains of the wet season across the north.

South-west farmers had a slightly drier-than-average winter and see the potential for higher rainfall as a boost to a season now shaping up well.

Dairy farmer Joey Conheady, who milks 610 cows at Garvoc, said he had been "thrilled" with the rain so far this spring.

"We will never complain about having rain," he said.

"We are wet at the moment and if that keeps us pushing in to summer, at the end of the day rain is rain, it's money into the Warrnambool economy and that's magnificent."

But Mr Conheady said he was also wary of weather predictions.

"Forecasts are great and we take that on board, but also in the last couple of years we were forecast for a dry spring and then had a lot of rain," he said.

Cobden Craig Dwyer echoed the sentiment, saying the past winter "couldn't have been any better".

"It's as good as it gets," Mr Dwyer said.

"It was drier, we got an early break, then a dry winter then a wet tail end of August."

He said high rainfall could also make accessing paddocks difficult during the farm's silage window between October and November.

"Given we are wet farm here it's towards mid October before we look at putting a tractor on a paddock and it could be somewhat later this year," Mr Dwyer said.

Climatologist with the Bureau of Meteorology Jonathan Pollock said La Nina effects may not be felt as strongly in south-west Victoria.

"We are expecting an above average rainfall for northern and central Victoria, there's a more than 80 per cent chance of this," he said.

"But those strong chances don't necessarily extend to south-west.

"We still expected a wet outlook for Warrnambool, but chances of flooding aren't as high as central."

Mr Pollock expects the temperature to rise across Australia.

"Along the coast, there will be a warmer than normal day time until December and night time, for most of the country, will also have warmer temperatures."

The bureau's manager of climate operations Dr Andrew Watkins said south-eastern Australia may get more rainfall into the summer months.

"This can wet up the soils and make the chance of widespread flooding," he said.

"Typically, (there will be) more rainfall, wetter soils, higher rivers, more water going into our storages as well which is a good thing in many areas.

"It reduces the risk of getting those really extreme heat waves, but unfortunately, the heat waves we do get tend to be longer in duration and could be more humid.

"In terms of fires, it reduces the fire risk a little, but of course, south-eastern Australia, one of the most fire-prone areas in the world, we're not going to get through a summer without seeing any fires."

Warrnambool has recorded a wetter-than-average September this year.

The BoM's rainfall gauge at Warrnambool airport recorded 102 millimetres of rain, above the 75-millimetre September average since records began there in 1998.

More than 40 millimetres of rain fell on a single day, last Friday, bureau data shows.

The 16.5 degree Celsius mean maximum temperature for last month was slightly higher than average. The airport has typically recorded 16 degrees for September in the past 22 years.

Rain at Mortlake Racecourse was also above average, with 94 millimetres falling last month, above the 58-millimetre September average.

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