There have been more than 50 calls for help overnight to the NSW State Emergency Services as wild weather pummels the north of the state and parts of southeast Queensland.
The BOM is warning that wild weather in northern NSW this week will bring heavy rain, damaging winds, flooding as well as dangerous surf conditions.
The SES says more than 700 calls for help have been made since Friday and 57 overnight, while a severe weather warning for very heavy rainfall is current for the Northern River areas.
More SES personnel have been sent to the affected area to help after volunteers performed five flood rescues over the weekend in the northern rivers areas, Tweed Heads and Byron Bay.
The SES said heavy rainfall over Leycester Creek and the Wilsons River at Lismore is likely to reach the minor flood level (4.20 metres) around midday on Monday with roads and low lying farm land and rural properties most likely to be inundated with flood waters.
Further rises to the minor flood levels are possible at Billinudgel and Mullumbimby with minor flooding expected along Marshalls Creek and the Brunswick River.
During Monday and Tuesday, minor to moderate flooding is possible along the Bellinger River at Thora and Bellingen.
This will result in low lying areas being impacted by floodwaters along the Bellinger River, possibly impacting on the communities of Darkwood, Thora, Bellingen, Repton, Mylestom and surrounding areas.
The Tweed River at Tumbulgum is likely to reach the minor flood level (1.40m) on Monday with the high tide.
The SES says the flood situation is being monitored and revised warnings will be issued should the situation change.
People in areas likely to be impacted by flooding should refrain from driving or walking through flood water, take note of road closures and monitor emergency warnings and severe weather updates.
The BOM says thunderstorms could lead to the possibility of very heavy rainfall and dangerous flash flooding.
“At this stage, the widespread heavy rainfall is expected to ease late Tuesday or early Wednesday,” the BOM said.
“Thunderstorms may still produce localised heavy falls that may lead to flash flooding during Wednesday.”
The BOM also warned damaging winds averaging 60-70km/h were likely along NSW’s coastal fringe from Yamba to as far south as Crescent Head on Monday.
Waves possibly exceeding five metres in the surf zone could also be expected from Yamba to Port Macquarie.
Communities in flood-prone areas spent Sunday sandbagging low-lying areas and preparing properties.
Meanwhile, a surface trough was expected to deepen off the southeast Queensland coast on either Sunday night or Monday morning, the BOM said.
A low pressure system is likely to form along this trough and approach the southeast Queensland coast.
The BOM said damaging winds, heavy rainfall, abnormally high tides and damaging surf could be expected in the Gold Coast, Brisbane, Moreton Island, North Stradbroke Island, Sunshine Coast, Fraser Island, Caboolture, Cleveland, Redcliffe, Jimboomba, Beaudesert and Springbrook.
Meanwhile, a flood warning is in place for Western Australia’s De Grey River catchment after a tropical low dumped heavy rain from the Pilbara to the border with South Australia.
The system crossed the coast near Port Hedland on Friday and it started bucketing down as the weather system moved southeast towards the Goldfields.
A flood warning was issued on Sunday night for residents in the Fortescue River catchment.
Warnings were also issued for the Sandy Desert, Warburton District and Salt Lakes District rivers.