RESIDENTS in northern NSW are on alert for torrential rain, heavy winds and flash flooding as a severe weather system moves south in the wake of Cyclone Debbie.

While the monster cyclone may have been downgraded to a tropical low, Sydney and most of NSW will certainly feel the effects over the coming days.

FOLLOW OUR COVERAGE OF CYCLONE DEBBIE HERE

As north Queensland wakes up to devastation, the weather front is making its way south east towards Sydney and is bringing torrential rain, with over 100mm expected in some parts and gale force winds.
 

Bureau of Meteorology forecaster Rob Taggart said the system is bringing humidity down into Sydney, that's why the city can expect a humid day today with a top of 29C forecast.

"A whole lot of humidity is being dragged by this system across eastern parts of NSW. That is going to interact with a cold front coming for NSW on Thursday," Mr Taggart said.

"Because of that, there will be widespread rainfall over the eastern half of NSW on Thursday, with the heaviest falls to be around the northern rivers."
 

The rainfall totals on Thursday will be 100mm or more in many parts of the state, with some locations in the northern rivers predicted to get a dumping of 300mm or more, as a result of ex-cyclone Debbie.

Tweed, Lismore, Coffs Harbour and even as far south as Taree as predicted to be among the wettest areas.
 

Mr Taggart said at this stage no flood warnings have been issued for Sydney, but the city should expect a drenching and gale force winds along the coast.

"Thursday is going to be a pretty soggy day and we are forecasting rain 20mm or more widespread. The rain could be heavy at times."

"There will be a southerly change coming throughout the day, but the winds will pick up in the evening along the coastal fringe on Thursday evening."

Some flood watches have also been issued for most of the rivers in the northern district.