Australia's east coast is only set to get wetter as it becomes bogged down in a major rain event that has led to some of the biggest downpours in half a century in places. Roads are clogged, offices flooded and train lines have closed.

Forecasters have said it's going to be "massive" with the trough sticking around right through the weekend and into next week with flash flooding and strong winds on the cards.

On Friday morning, the Bureau of Meteorology (BOM) issued a severe weather warning for almost the entire New South Wales coast for heavy rainfall, flash flooding, "abnormally" high tides and dangerous surf.

A low pressure trough is dumping rain on a huge swath of the country with Sydney sodden with its highest 24 hour rain total since November 2018, Brisbane drenched and Byron Bay seeing its biggest downfall for almost half a century.

Advertisement
A flooded office in Sydney's CBD this morning after heavy rain hit the city. Photo / News.com.au / Supplied
A flooded office in Sydney's CBD this morning after heavy rain hit the city. Photo / News.com.au / Supplied

"In some places it will be the equivalent of three months' rain falling in a week," Sky News Weather channel Meteorologist Tom Saunders told news.com.au.

"Heavy rain will continue along the NSW coast all weekend. For many regions it will be the heaviest rain in years, including Sydney."

An urgent weather warning is now in place for an huge 1000km stretch of the coast from Sydney to beyond Brisbane.

Meanwhile, in Western Australia, a cyclone is set to hit land as early as tomorrow with supermarket shelves stripped bare and locals preparing to take shelter as winds of 225km/h or higher smash the Pilbara coast.

Sydney saw 79mm of rain drench the CBD overnight. More rain has fallen in six hours than has fallen in the last three months combined. The Harbour City could squelch its way through its wettest 24 hour stretch for years today.

Pictures have shown Sydney CBD offices flooded with water as the rain has seeped into buildings.

By 9am, Byron Bay — the easternmost point of mainland Australia — had received 275mm of rain in 24 hours. That's a feat not seen for 46 years.

Sydney rain radar.
Sydney rain radar.

If the BOM's upper rain forecast is correct, Sydney could see just shy of 400mm of rain over the next week. That's more than three months' worth of rainfall in a single week.

Advertisement

"It is hammering down with rain," Mr Saunders said.

It's possible the rain may ease slightly overnight but it will come back again with heavy rain for tomorrow.

"The weekly total will be massive. We've already had over 100mm and we will see over 200mm so we're looking at around 300mm in a widespread area."

WHAT'S CAUSING ALL THE RAIN?

Flooding has slowed several roads on Sydney's north shore including Pittwater Rd in Dee Why and Pennant Hills Rd in Thornleigh. The T1 Western and North Shore line is suffering delays due to a tree that came down in the soggy conditions. The T2 Inner West and Leppington line is also delayed.

NSW Rural Fire Service Commissioner Shane Fitzsimmons, who has been battling bushfires for months, tweeted this morning that it was, "So nice listening to rain falling last night".

Mr Saunders said the rain could bring drought relief and extinguish some fires.

"The positive Indian Ocean Dipole climate system has broken down and the monsoon is active across the northern tropics.

"Also we have a very moist east north easterly along the east coast which is pumping moisture in from the Coral and Tasman seas. This moisture is linking with a coastal trough to cause the torrential rain."

Bega and other parts of the south coast have yet to fully feel the rain – but it's coming. As much as 225mm of moisture could be dumped on areas previously scorched by bushfires. Canberra could get 75mm of moisture.

Brisbane has seen 96mm of rain since yesterday afternoon.

South East Queensland and northern New South Wales is set to be absolutely drenched. Photo / News.com.au / East Coast Weather / US National Weather Service
South East Queensland and northern New South Wales is set to be absolutely drenched. Photo / News.com.au / East Coast Weather / US National Weather Service

The Courier Mail has reported that major roads are flooded including parts of Gympie Rd at Carseldine and the M1 Bruce Highway at Griffin.

Maryborough on Queensland's Fraser Coast had received 183mm of rain with the Mary River bursting its banks.

The Bureau now has an urgent warning in place for a 1000km stretch of Australia – from Sydney to Caboolture north of Brisbane. Flooding could occur along rivers up and down the east coast including in major cities.

"We're only about half way through this event," Mr Saunders said.

The BOM has said a coastal trough near the coast is bringing increased rainfall.

"This trough is expected to deepen and gradually shift southward, increasing rainfall along the central and southern parts of the coast and adjacent ranges during Friday and over the weekend," the weather bureau stated.

The NSW Central Coast and south coast are at particular risk.

"Heavy rain resulting in flash flooding along the coast is a real possibility," NSW SES Deputy Commissioner Daniel Austin said earlier this week.

"Flash flooding is incredibly dangerous. I'm urging motorists, please stay safe on the roads – pull over if the rain becomes too heavy or if you can no longer see where you are going. Make safe decisions and never enter floodwaters."

In Brisbane, where many suburbs picked up over 100mm of rain yesterday, heavy rain will continue for the next few days. More than 200mm could fall in the coming seven days.
"Over the next eight days we expect 100-300mm on top of what we've already had on the NSW coast, up to around 50-100mm for the top of the Ranges and then less than 50mm west of the Ranges," Sky's Mr Saunders said.

CYCLONE DAMIEN APPROACHES

As the humid easterly pumps moisture into Queensland, a trough into the west is pushing showers down as far as Victoria and even parts of South Australia. But Melbourne, Adelaide and Perth should remain mostly dry.

Sydney is heading for a maximum of 23C on Friday, Melbourne 26C, Brisbane 29C, Perth 30C, Adelaide 31C, Hobart 20C, Canberra 23C and Darwin 34C.

Meanwhile, Tropical Cyclone Damien is due to make landfall in Western Australia's northwest Pilbara region over the weekend, with heavy rainfall and flooding expected.

By the time Damien hits land it could be as strong as a category 4 storm. It's track has it currently on course to hit land just north of Karratha on Saturday.