NSW SES has issued evacuation orders for parts of north and south Lismore and low-lying parts of Kyogle as "exhausted" residents prepare again for torrential rain and yet more flooding.
Residents of those areas have been told to leave by 10pm on Monday, with moderate to major flood warnings issued for the Wilsons River.
The orders issued on Monday evening come amid fears the already-soaked Northern Rivers region could experience six hour totals of 80-140mm, and isolated falls of up 200mm.
The epicentre of unprecedented floods last month - still in the midst of a mammoth clean-up - is on the frontline along with Tweed Heads, Evans Head, Yamba as well as Grafton and Coffs Harbour.
"Everyone is a bit shell-shocked, they're in disbelief, they're exhausted ... and others are frantically trying to prepare the best they can," Lismore Councillor Adam Guise told AAP on Monday afternoon.
"It's all a bit uncertain and people are pretty devastated and scared facing the prospects of another major flood."
He said he was in preparation mode, evacuating his pets and other possessions to higher ground.
"Things could escalate quickly on these rivers particularly with these isolated falls," Dean Narramore of the Bureau of Meteorology told reporters, warning of life threatening flash flooding.
He said severe weather warnings are in place from the Queensland borders to Coffs Harbour, spanning 450 kilometres of coastline.
"The rain from this system shouldn't be as heavy as the event at the end of February and early March for most areas," said Ben Domensino of weather monitoring service Weatherzone.
But he warned "catchments are still waterlogged from that event, which will exacerbate the risk of flooding during the next 48 hours".
The rain will continue into Tuesday and only begin to ease that afternoon and evening.
"These things come with exceptionally short, sharp bursts of rain which pose a risk to life and property," Mr Austin told reporters.
A flood watch is in place for the Northern Rivers, Mid North Coast, Hunter, Hawkesbury Nepean and North Western NSW Rivers.
Moderate to major floods are possible on the Richmond, Wilsons, Orara and Bellinger Rivers from Tuesday, as heavy falls hit already-saturated catchments.
Mr Austin said Warragamba Dam in western Sydney, which spilled earlier this month, could also begin spilling as early as Monday evening.
Meanwhile, Flood Recovery Minister Steph Cooke said 27 recovery centres run by Resilience NSW have been set up across the state, with the majority of them in northern NSW.
With La Nina drenching Australia's east coast for the second year in a row, fatigue has set in.
"It's a phenomenon that lasts over our summers and will dissolve by autumn," Dr Nina Ridder of UNSW's Climate Change Research Centre told AAP.
"La Nina events are likely to bring more extreme rainfall to Australia.
"We're definitely seeing the change in global weather patterns because of climate change".
