A Bureau of Meteorology Victoria forecaster said storms in the Warrnambool and Hamilton areas would occur this evening but the main rain band with thunderstorms would hit in the early hours of Friday morning with between 20-40mms falling.

Those falls were expected to be the heaviest during the four-day rain event, the forecaster said.

The rain was expected to ease late Friday and early Saturday but consistent downpours were expected to occur throughout much of Saturday.

On Sunday, the rain could ease to showers but the forecaster said Warrnambool would still “be in the firing line” from a low pressure system, the forecaster said. 

Local SES units are preparing for flooding and the downpours are expected to cause significant damage to crops as well as hay still to be baled.

UPDATE, 2.51PM: There have been power outages across the south-west with Powercor reporting almost 600 customers affected.

According to the Powercor website there have been outages in Allansford, Peterborough, Nullawarre, Niranda, Curdievale, The Cove, Brucknell, Ayrford, Purnim, Mepunga and Naringal.

The power company says it expects the electricity to be restored by 6pm.

There have also been outages recorded in Tyrendarra, Codrington, Macarthur, Branxholme, Heywood and Bessiebelle.

UPDATE, 12.36PM: The Warrnambool SES unit will make available sandbags to the public from its Walsh Road headquarters from 6pm-7pm tonight to help the community prepare for the heavy rain event that is expected to dump up to 120 millimetres on the region between today and Sunday.

Warrnambool SES controller Giorgio Palmeri said the bags will be empty and people will have to source the sand to fill them at this stage.

Mr Palmeri said all the unit’s volunteers, including crew for its Swift Water Rescue Craft, had been put on standby in readiness for the rain event.

He expected the unit would have between 25-30 volunteers ready to help people deal with flooding and other emergency events.

Representatives from all SES units in the south-west will meet tonight at 6pm by teleconference to prepare for the forecast deluge. 

Warrnambool received about 5mm of rain between 9am and 12.30pm today. 

UPDATE, NOON:

Today’s twilight Port Fairy Community Race Day meeting at the Warrnambool Racing Club will proceed despite predictions of a heavy storm.

Warrnambool Racing Club chief executive Peter Downs said heavy rain was not expected to hit Warrnambool until about midnight and stewards had cleared the track for racing.

Mr Downs said there was plenty of room indoors for people to enjoy today’s race meeting that begins at 4pm.

Premier Daniel Andrews has warned Victorians to exercise caution during the forecast downpour.

Up to 120 millimetres is expected to fall in the south-west between today and Sunday.

“This is a very serious matter and one that will pose a very severe challenge to communities right across the state and will be a direct challenge to public safety,” Mr Andrews said.

UPDATE 11.06am: 

A large pressure system near New Zealand continues to direct a hot and humid northeasterly airstream over Victoria.

Three day totals of around 100-200mm are expected acoss most of northern and central regions of the state. Elsewhere totals are likely to be between 30 and 100mm. Over the northeast ranges totals may exceed 250mm.

Locations which may be affected include Warrnambool, Horsham, Mildura Bendigo, Shepparton, Seymour, Maryborough, Ballarat, Geelong, Melbourne, Wodonga, Wangaratta, Traralgon and Bairnsdale.

The weather bureau is predicting up to 120mm of rain to fall in the south-west between today and Sunday.

The Bureau of Meteorology has issued a severe weather warning for the state, particularly heavy rain.

It says heavy rain and scattered thunderstorms may lead to flash flooding. It expects the heavy falls to develop in the Portland area on Thursday night.

A flood watch has been issued for the Hopkins River and Lake Corangamite catchment over the weekend. After Warrnambool recorded a top temperature of 34 on Wednesday and Port Fairy hit 35, the rain has already started. Hamilton had 1.2mm in a short burst just after 10am while in less than 0.5mm has been recorded at Warrnambool airport, according to the bureau. 

The State Emergency Service is urging people to be safe by:

* Not walking, riding or driving through flood water; 

* Keeping clear of creeks and storm drains; 

* Being aware that in fire affected areas, rainfall run-off into waterways may contain debris such as ash, soil, trees and rocks and

* Being alert that in areas recently affected by fires, heavy rainfall increases the potential for landslides and debris across roads.

More to come