A severe weather warning has been issued for the already flood-ravaged northern region of NSW where communities continue their massive clean-up.
Heavy rainfall with a risk of possible life-threatening flash flooding is predicted for the Northern Rivers, North Coast and Northern Tablelands on Monday and through to Tuesday, Bureau of Meteorology senior meteorologist Jonathan How told AAP.
Downpours of between 30 and 60mm were recorded on the coastal strip from Tweed Heads and Byron Bay overnight, Mr How said.
Those falls were on top of rainfall totals between 100 and 200mm recorded over Saturday and Sunday.
He said heavy falls will push down from the Queensland side of the border later this morning and into the afternoon, and then "really peak this afternoon and into the evening".
Those falls will continue into Tuesday and only begin to ease on Tuesday afternoon and into the evening.
The forecast zone includes Tweed Heads, Murwillumbah, Byron Bay, Lismore, Yamba, Grafton, Coffs Harbour and Dorrigo, where six-hourly rainfall totals of between 80 and 140mm are predicted.
"All of those locations could see those really heavy falls, but it does come with a caveat that those flows will be with the thunderstorms, Mr How said.
He stressed while the conditions were similar to those in the recent Lismore flood, the outcome was not predicted to be as widespread and severe.
Lismore's mayor Steve Krieg said the next two days would be critical for how Lismore is going to fare over the next week.
"It won't bloody stop raining up here," told the Nine Network on Monday.
"This is a major development, this weather front. If our river rises, we're going to start the evacuations today just to be cautious."
Rough seas are expected along the Byron Coast on Tuesday, and dangerous swells will also hit shores on the Macquarie and Hunter Coast on Wednesday.
A flood watch is in place for the Northern Rivers, Mid North Coast, Hunter, Hawkesbury Nepean and North Western New South Wales Rivers.
Moderate to major floods are a possible on the Richmond, Wilsons, Orara and Bellinger Rivers from Tuesday as heavy falls hit already-saturated catchments.
Minor to moderate flooding is also a risk for parts of the Northern Rivers, the North Coast, Hunter, Hawkesbury-Nepean and North-Western NSW rivers.
"It won't bloody stop raining up here," Lismore Mayor Steve Krieg told the Nine Network Monday.
Australian Associated Press
Sign up for our newsletter to stay up to date.