A low pressure system over central-eastern Queensland and a high pressure system over the Tasman Sea are dragging a humid tropical air mass over parts of NSW as the remnants of ex-tropical cyclone Debbie collide with a large pool of moist air from the south.

The Bureau of Meteorology issued a severe weather warning for heavy rain and damaging winds over the course of Thursday and Friday for most of northern NSW and coastal sections of the Mid North Coast.

"A low pressure system over central-eastern Queensland and a high pressure system over the Tasman Sea are dragging a humid tropical air mass over parts of NSW," the bureau said.

"Heavy rainfall over northeastern NSW is likely during Thursday and Friday as a cold front approaches from the south-west and interacts with this humid air mass."

NSW SES Mid North Coast Region is urging residents to use make preparations for the possible severe weather predicted by cleaning roof gutters, securing down loose items around outdoor areas, and by monitoring the severe weather warning updates from the Bureau of Meteorology.

NSW SES Mid North Coast Region Controller Tony Day said the remnants of ex-tropical cyclones are difficult to predict.

“With the catchments saturated by the recent rain, there is potential for damaging winds averaging 65km/hr and gusting up to 90km/hr, to bring down trees and threaten properties,” he said.

“We have on standby a number of NSW SES volunteer storm and water damage teams and flood rescue technicians.

“These systems are notoriously difficult to predict so we are asking the community to not drive through flood water, to keep children away from flooded drains and creeks and to prepare your properties now for high winds.”