Heaviest rain in four years with storms ahead
Some towns have already seen their heaviest rain in years with dangerous storms brewing in NSW and Queensland ahead of the weekend.
Dubbo in New South Wales recorded 65 millimetres of rain, its wettest day in four years, as Sky News forecasters said there had been "exceptional rainfall in many areas".
Rain showers and storms continued over NSW and Queensland overnight, with the deluge concentrated along the east coast as inland areas dried up. The downpour is expected to increase in south-east Queensland over the weekend, as the "significant rainfall" is set to collide with a "second rain event"
Town sees heaviest rain in four years
Parts of New South Wales have been lashed by their heaviest rain in years with dangerous storms expected in NSW and Queensland over the weekend.
Dubbo in regional NSW experienced its wettest day in four years with 65 millimetres of rain as Sky News forecasters warned of "exceptional rainfall in many areas".
The deluge overnight is now concentrated along the east coast and expected to worsen, with downpours and thunderstorms predicted for southeast Queensland.
Forecasters said that the region from Nambucca Heads down to Forster in NSW, with Port Macquarie in the middle, could expect the most rainfall, with 150-200mm on Friday alone and the threat of damaging winds.
The showers will move further inland on Saturday with 50-150mm of rain expected on the NSW coastline as the downpour spreads into a wider area.
Some rainfall will drift across Victoria into the Riverina of NSW.
'Dangerously wet' warning for 900km of coast
The Bureau of Meteorology (BOM) has said there is a double whammy of rain dangers: already sodden soils that can't absorb any more rain and persistent drizzle interspersed with localised heavy downpours that could see twice the mount of rain of areas close by.
The BOM has said people living along a 900km stretch of coast, from Byron Bay to Wollongong, should be aware of the dangers.
"Those two factors combined: the wet soils and very heavy rainfall, can change from what may seem as inconveniently wet conditions to dangerously wet conditions," said BOM metrologist Agata Imielska on Thursday afternoon.
It came as forecasters warned two-thirds of Australia was likely to see a soaking with a severe weather warning for heavy and "intense" rain and flash flooding in place for the NSW coast.
'Many months of rain' could fall in just days
Some communities have seen their wettest March in years and forecasters have warned that "many months of rain could fall" in the coming days.
Coonamble, in central NSW, and Yeppoon, near Rockhampton in Queensland, both saw their heaviest March rainfall in two years.
As we head into Friday the wet weather edged down from the Capricornia region on Queensland and northern NSW and the mid north coast towards the Hunter and Sydney.
At the same time heavy falls can also be expected in inland areas, including the outback, in a line form the Northern Territory down to northern South Australia.
Sky News Weather meteorologist Alison Osborne said it was "an absolute deluge".
"There is some uncertainty about where the heaviest falls will be this weekend. There is a risk of that flooding reaching Sydney and the rain spreading into northern and eastern parts of Victoria."
"With 150-300mm forecast in the northern half of NSW for some that will be almost a month's worth of rain in just a few days. In the outback (where less rain falls) there could be many months' worth of rain in the next few days."
Sydney dam could spill in deluge
The Bureau of Meteorology said it was a "possibility" the Warragamba Dam in NSW could spill, which could lead to minor flooding along the Nepean.
The NSW State Emergency Service (SES) has 4500 volunteers in Sydney alone on standby to deal with the deluge. A further 2000 are ready in northern NSW, which is expected to bear the brunt of the system on Friday.
There are flood warnings in place for multiple NSW rivers including the Nepean, Hawkesbury and Georges.
Dams in the Greater Sydney region are currently 93.3 per cent full with Warragamba, the largest serving the city, at 96.4 per cent capacity.
However, the BOM said a spill was unlikely in itself to cause major flooding.
Showers and storms to collide with second 'rain event'
A weather system in the north of the country is expected to collide with the rain event in eastern Australia, bringing further downpours to the coastline into next week.
Showers and thunderstorms hit the north-west of the country overnight with Katherine experiencing heavy rain in the past few days.
Those showers will filter south through the Kimberley into central parts of Australia and then down into northern parts of South Australia, with heavy rain developing through the weekend.
This weather system will collide with the eastern weather system shifting westward and a low pressure system will form, linked to heavy rain in northern NSW on Monday.
This second event will keep drifting east, bringing widespread rain across the Murray Darling basin, before moving out to sea on Wednesday or Thursday as a few showers hold on.
Parts of NSW can expect more than 150mm of rain, with 25-50mm expected in many parts of Victoria and Queensland, and 50mm in parts of northern Australia.
Originally published as Heaviest rain in four years with storms ahead