A severe weather warning for the already flood-ravaged northern region of NSW has been issued by forecasters, as communities continue in their massive clean-up.
Heavy rainfall with a risk of possible life-threatening flash flooding is predicted for the Northern Rivers, the North Coast and the Northern Tablelands on Monday and through to Tuesday, Bureau of Meteorology Senior Meterologist Jonathan How told AAP.
Heavier falls have already been recorded on the coastal strip from Tweed Heads and Byron Bay overnight of between 30 to 60mm, How said.
Those falls were on top of rainfall totals of between 100 to 200mm recorded over Saturday and Sunday.
"We are expecting the rain to really ramp up today.
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 will 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 to 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.
"With thunderstorms, we tend to see sometimes lines of thunderstorms basically move over the same town over hours and hours," Mr How said.
"It's a very similar set-up to what we saw earlier this month (with Lismore) but it will depend on where those lines of thunderstorms do form."
"That's where we'll see the 100 plus millimetres.
"Pretty much anywhere along the coast towards the ranges is potentially under threat of life-threatening heavy rainfall from today."
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.
"It's not expected to be as bad as what we saw earlier this month," he said.
"We are expecting fairly widespread minor to moderate flooding, but not at this stage expecting the significant, major widespread flooding.
Mr How said many communities remained sensitive after widespread damage, and the risk of dangerous conditions was still active.
"It won't bloody stop raining up here," Lismore Mayor Steve Krieg told the Nine Network on Monday.
"The forecast doesn't look good ... the next two days is critical for how Lismore is going to fare over the next week.
"This is a major development, this weather front. If our river rises, we're going to start the evacuations today just to be cautious.
"But there's a lot of infrastructure that's been temporarily put in place that we're going to have to pack up and move out of the CBD area."
The public school in the riverside town of Woodburn is expected to reopen on Monday, and a number of businesses in the Northern Rivers were planning to recommence trading.
"All these people are living on the edge at the moment," the mayor said.
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