Perth could see five times its monthly average rainfall in one day when the remnants of ex-tropical Cyclone Joyce arrive in the metro area after tracking south from the Kimberley.
The cyclone has been downgraded to a tropical low, but the Bureau of Meteorology warned the system was still bringing damaging winds and the risk of flooding.
BOM duty forecaster Pete Clegg said Perth residents could be in for a surprise.
"Five to 10 millimetres would be the average amount of rainfall that we'd get out of a cold front in Perth," he said.
"You're talking of getting 30 to 50 millimetres — obviously a fair bit more than that — and definitely not what you'd [ordinarily] get in summer."
Rain welcomed in the north
The managers of Mandora Station in the Kimberley, Ben Mills and Caitlin U'Ren, were up early to start the clean up after the system passed through, and said things were looking good.
"If we could have cyclones like her all the time that just drop a big heap of rain but not much damage, that would be great." Ms U'Ren said.
"It's nice and wet, the grass is already starting to grow and green-up surprisingly, there's a little bit of damage with branches around but it's looking pretty good.
"There's a fair bit of water on the airstrip, but other than that it's soaking in well."
Ms U'Ren said the yearly average rainfall for Mandora Station was 350 millimetres, but it received more than 200mm in just 24 hours as the system passed off the coast.
"It's a really good start to the season, if we get some more rain in the next couple of weeks it's going to be a bumper."
Rain brings renewal
The popular Karijini National Park near Tom Price has remained closed after rangers moved people out of the campsites and Karijini Eco Retreat on Friday.
The Department of Biodiversity, Conservation and Attractions' Pilbara regional manager, Alastair McDonald, said it was not safe to allow the public in the 500,000-hectare park.
"The typography and nature of the landscape make these areas fairly dangerous in high rainfall conditions because the areas tend to flood quite quickly," he said.
"There are quite a few floodways on these roads and people who aren't familiar with driving conditions in these areas can underestimate water levels at these points and find themselves in trouble and cause accidents unnecessarily."
More than 200,000 people visit Karijini each year, but with more rain expected it is likely to remain closed until Monday.
However, Mr McDonald said visitors in the coming weeks will be treated to some extraordinary sights as water flows through the gorges and waterfalls that are usually dry, and the wildlife flourishes.
"Fortunately wildlife species in this area have evolved for these sorts of events," he said.
"In particular, in these arid environments, the response of wildlife it usually very positive, the area starts greening up, and we see an increase in wildlife activity, breeding and the like."
The Millstream Chichester National Park in the Shire of Ashburton has also been closed, after the water level of the Fortescue River rose significantly.
Deluge could reach south of Perth
Perth could see heavy rain from late Sunday through to Tuesday morning.
"It's still a little bit uncertain exactly how much we'll get, because as far as the track of the low as it comes down through the South West Land Division it may push offshore, in which case those heavier falls could remain to the north-west of us," Mr Clegg said.
"But certainly it looks likely that we'll see at least more rainfall than you'd expect for an average January day.
"At this stage I'd say there's a pretty good chance by Tuesday we'll be seeing rainfall through a good portion of the South West Land Division, anywhere even south-west of Perth across to Southern Cross and then down across to the Bremer Bay area.
"I think there's a good chance that whole area could receive some amount of rainfall. In terms of how much, again it's little bit uncertain at this stage, but definitely in the order of above 10 millimetres on the Tuesday, but definitely even upwards of 30 or 40 millimetres is a possibility."ABC