WA southwest, Perth brace for wild weather

Western Australia's southwest is bracing for damaging winds as a cold front brings wild weather and the chance of flash flooding in Perth.

The cold front is forecast to move across Bunbury, Busselton, Dunsborough, Margaret River, Augusta and Manjimup on Saturday evening, the Bureau of Meteorology says.

A severe weather warning is in place amid concerns thunderstorms, rain and and winds of up to 100km/h could damage homes and property.

Gusts in coastal areas south of Augusta could reach 125km/h.

Conditions are not expected to be as severe in Perth, but residents should be prepared for a period of gusty winds and possible flash flooding from the Murray River and Harvey River catchments.

A flood watch has been issued for Perth, Mandurah, Bunbury, Preston River, Busselton, Margaret River and Blackwood River in the southwest.

DFES advises farmers to shift livestock and equipment to higher ground and for households to check their gutters for debris and secure loose objects including children's trampolines and play equipment.

A second, stronger front is expected to pass through WA's southwest on Sunday night and early Monday morning.

The Bureau of Meteorology warns Sunday's front will bring waves off the capes up to eight metres high, with 6m to 7m surf at Perth beaches.

About 60 millimetres of rain is expected over the weekend with falls this season so far above average at 321 millimetres. The average winter total is 473.5mm.