The weather bureau's Richard Carlyon said the storms would start in the state's far north-west tonight and sweep across the state tomorrow.

"Areas likely to be affected by the heavy rain are the northern and western parts of the state, and also down into the south-west," he said.

"The actual peak of the rain is going to be over the north-west ranges, where fall totals of 75 millimetres to 100 millimetres are possible."

The rain is not all the Warrnambool and District Football Netball League grand finalists and Hampden league second semi-finalists will have to contend with.

"Wind is also something we might be warning for," Mr Carlyon said yesterday.

"Very gusty winds around this low-pressure system, particularly in elevated areas and the south-west of the state, might see some gale -force winds Saturday."

With rainfall up to 30mm predicted, authorities are monitoring river systems that have already been hit by winter deluges.