The Bureau of Meteorology has warned Western Australia to brace for a 'rare' and 'dynamic' storm system developing off the coast causing extreme weather conditions.
Tropical Cyclone "Mangga" hitting the Cocos Keeling Islands on Friday is the worst of the low pressure system off the west coast, but the fallout will move east on a collision course with WA.
"The weather situation is dynamic and complex as a tropical system interacts with a cold front and we're expecting one or two low pressure systems to form and impact the west coast on Sunday and into the early hours of Monday morning," BOM WA State Manager James Ashley said on Saturday.
Strong winds up to 130km/h and heavy rain will start on the upper part of the WA coastline on Sunday morning and move south by the evening and into Monday.
With seas to be whipped up by the storm, peak wave heights are predicted to hit around 8 metres on Monday.
In the state's capital Perth, northerly damaging winds will hit on Sunday and won't ease up until Monday afternoon, and 30-40mm of rainfall should be expected.
"Rainfall with be widespread across the state with isolated falls from the Kimberley to Karratha up to around 100mm, and rainfalls on the south over 50mm, and that will extend inland up to 10-20 mm or more," Mr Ashley said.
"The winds will build up the seas against the coast and a storm tide is expected which can be particularly dangerous and could flood low lying coastal areas.
"This is a really rare event for WA. Not only is it unusual for this time of the year, but it extends across a large part of the state."
By tomorrow morning weather officials are hoping to improve on pinpointing more exact areas where the most severe conditions may occur.
Department of Fire and Emergency Services (DFES) Rescue Branch Manager Jon Broomhall urged all WA residents to use their Saturday preparing for the extreme weather to come.
"We've still got time to prepare," he said.
"We're asking the community to secure their properties now. They need to clean up their gardens, refuse, secure furniture, trampolines, toys, anything loose in the backyard.
"If you're undertaking planned burns for hazard reduction, they need to be extinguished now.
"Tomorrow do not go out on the water."
DFES confirmed they have been in discussions with the Defence Force locally and that they were "on standby", should their assistance be needed.
"It's a once in a decade type system," Mr Broomhall said.
"Normally our storms come from the southwest, but this is coming from the northwest.
"Our crews in the SES are on call but you need to stay up to date on Emergency WA.
"We have extra volunteers to man phone lines. We're prepared and we ask the community to be prepared as well."