Perth has just experienced its wettest month in 14 years, but the city is still behind on its year-to-date rainfall average, after a parched summer and autumn.

Key points: June has been an "exceptionally" wet month for Perth, but it follows a dry start to the year

June has been an "exceptionally" wet month for Perth, but it follows a dry start to the year This means the city is still some way short of reaching the average rainfall for the year

This means the city is still some way short of reaching the average rainfall for the year The weather bureau says despite the rain, parched soil means flooding has been minimal

The city's official gauge in Mt Lawley clocked up 205 millimetres by Thursday afternoon, making it the wettest month since June 2005.

The June average for the Mt Lawley gauge, which has been collecting data since 1993, is 124.5mm.

"We've recorded the third-wettest June on record for Mt Lawley. So it has been exceptionally wet this month," Bureau of Meteorology spokesman Neil Bennett said.

But the June deluge has failed to catapult the city to its year-to-date rainfall average of 302mm.

Parched soil soaks up falling rain

Up until Thursday afternoon the year's rainfall total stood at 280mm.

"So even though June has been very wet, we're still some way short of where we should be by now," Mr Bennett said.

"The reason for that is the fact that we had such a dry start to the year and indeed a dry end to last year.

"That has led to the lack of flooding. If there was a lot of sub-soil moisture, if the catchments had been primed by having even what would be described as a normal start to the season, then we could well have seen some flooding issues with the sort of rainfall that we've been receiving.

"We haven't seen that because the soil is so dry that the rain that's falling at the moment is being completely soaked up."

It's been a wet and windy start to winter in Perth. ( ABC News: Andrew O'Connor )

In decades gone by, falls of 200mm or more in June were considered the norm.

But since 1970 average rainfall in the south-west of WA has decreased by about 20 per cent, meaning that such totals are now an anomaly.

"The wettest June that we've recorded was 476.1mm in 1945," Mr Bennett said.

"So to get 180 to 200 millimetre falls in Perth in June was not all that unusual.

"That is the effect that the drying climate has had on the rainfall in Perth."

Rain shadow effect blocks rain on south coast

The heavy rainfall has been produced by a series of cold fronts sweeping up from the Southern Ocean and combining with moisture-rich cloud bands streaming in from the north-west of WA.

"When the two combine and work together you get these prolonged periods of heavy rainfall, which lead to the 50–80mm falls," Mr Bennett said.

"If the fronts are just working by themselves, a very strong front will probably deliver around 20–30mm but when they combine with these rain bands that come down from the north-west, that's when you can get these high totals and we've had two of those this season."

Perth experienced its wettest month in more than a decade. ( Supplied: Bureau of Meteorology )

The south-west of the state has been soaked as a result, but parts of the south coast have largely missed out, as ranges to the north of the area have blocked the heavy falls.

"In terms of the wettest areas, the west coast definitely, and especially the south-west coast — so the Margaret River area, Capel, those places have been incredibly wet," he said.

"Large strips of the west coast going all the way up to Geraldton have exceeded their monthly June average already.

"But the big areas that are missing out are the south-east coastal district and there's an area near Albany as well where they get a little bit of what we call a rain shadow effect.

"When the northerly or north-westerly winds are bringing the tropical moisture, they tend to get a rain shadow on the lee of those hills, so anything on the southern side of those hills tends not to see as heavy rainfall as on the northern side.

"So those areas are not quite as wet, but particularly that Esperance area when compared to the rest of the state, certainly for the last few weeks, but they've been dry for a long period of time now."