BOM issues severe weather warning for south-west WA as Perth's wet winter tops averages

As the Bureau of Meteorology issues a severe weather warning for WA's most populated region, Perth has seen wetter-than-average rainfall totals for each winter month for the first time since 1996.

A cold front delivered gusty showers and thunderstorms to south-western parts of the state from early Tuesday morning.

The front has caused the Bureau of Meteorology (BOM) to issue a warning for damaging winds and heavy rainfall that could lead to flash flooding.

BOM senior meteorologist Jessica Lingard said the metropolitan area could see widespread rainfall between 10 and 30 millimetres, while some areas could pick up as much as 60mm.

"It will reach the South West Capes early [Tuesday] morning and push through the metro area by around school drop-off time," she said.

"If we see any slow-moving thunderstorms or thunderstorms with a train effect — storms that follow one after another moving over the same area — [that will result] in isolated areas picking up higher rainfall totals."

The warning covers locations including Perth, Mandurah, Busselton, Bunbury, Manjimup, Margaret River and Moora.

Strong north-westerly winds with isolated damaging gusts of around 100 kilometres per hour are likely along the west coast and inland areas, and could bring down trees and power lines.

The windy conditions are due to ease later in the day, while the showery weather is set to continue into Wednesday.

Average exceeded

Perth needed 12mm of rain to surpass its monthly average for August, and by 2.30pm it had recorded 13.2mm. 

It meant Perth surpassed its average rainfall total for each of the three months of winter for the first time in almost three decades.

Ms Lingard said equipment failures in June and early July meant the bureau was missing several days of data from the Perth metro gauge.

In June this year, 101mm of rainfall was recorded in the Mount Lawley gauge with 11 days of data missing, falling short of the 127.1mm monthly average.

"However, having a look at the surrounding gauges across the metro area during those equipment failure days, it is likely that we saw above average rainfall in June," Ms Lingard added.

Nearby, Perth Airport saw a higher-than-average total of 153.8mm, while Swanbourne far exceeded its June average to record 182mm.

In July, the Perth metro gauge picked up just over 174mm, surpassing the monthly average of 147mm — even with the missing data.

In other parts of the state, higher-than-average rainfall totals have already been reached with less than two weeks to go until the end of August.

York and Beverley east of Perth have already recorded about 35 per cent more rainfall than average, while Gingin to the north has managed to pick up a higher-than-usual 132mm over the month.

Spring rain also ahead

Even if some places miss out on exceeding their monthly average today, another burst of showery weather on Wednesday could push them over the line.

The wet conditions are set to ease by Thursday with a high-pressure ridge extending in the wake of that cold front, delivering cool and mostly dry weather until the weekend when another soggy system is forecast to move through.

And as spring comes in September, Ms Lingard is anticipating a "flip-flop" between the beautiful spring weather and lingering winter conditions.

"We are still going to see cold fronts through September and even into October, but the length of time between systems will get longer and longer," she said.

"So we're not out of the wintry rainfall just yet and we're not just going to switch the rainfall off on September 1."