Severe weather and flash flooding to hit NSW

First the droughts. Then the flooding rains.

The maxim from Dorothea Mackellar's classic poem, ''My Country'' is about to ring true for NSW with what could be the heaviest rainfall in four years potentially breaking the state's crippling dry spell.

And while the deluges will be welcome news for farmers and fireys battling the dwindling water supplies and bush infernos all summer it has also triggered a severe weather and flash flood warning from authorities.

Sky News meteorologist Tom Saunders said if Sydney receives more than 168mm in a week, it will be the heaviest fall in four years.

Rain clouds roll into Emerald Beach in Coffs Harbour. Picture: Trevor Veale

Mike Funnell, Bureau of Meteorology manager of weather services in NSW and ACT, said the looming wet could be similar to June 2016, where rainfall travelled along the entire NSW coast over a three-day period, causing significant riverine and flash flooding.

A severe weather warning has been issued today for the fire-hit north coast including Lismore, Coffs Harbour, Grafton and Port Macquarie, with flash flooding predicted.

As a result, moderate flooding is expected at Nambucca River and Wilson River, south of Coffs Harbour.

Back on November 28, 2018, commuters struggled against torrential rain and gale force winds across Sydney. Picture: Nicholas Eagar

Warnings aside, Mr Funnell confirmed the forecast was promising news for bushfire and drought-affected areas.

Yesterday morning, there were 60 fires burning across NSW, some of which were still out of control.

"It does have the potential to be the most significant rainfall for the fire grounds this year," Mr Funnell said.

"It was only four days ago that we had six fires still burning at emergency warning levels.

"If the system tracks as we expect it to, we could see some significant totals that really give the fire agencies an upper hand."

Heavy rain is predicted along the NSW coast and inland.

He said while there will be some relief, there needs to be a series of these events to attack the rainfall deficiency in drought-affected areas.

BOM meteorologist David Wilke said there was no easy answer to how much rain would be needed to extinguish the bushfires.

"There's no clear-cut answer. For example, if you have a fire burning in undergrowth and canopy is above it, it can inhibit the rainfall.

"But generally speaking, you would need a steady soak for a number of days."

The inner city wasn’t spared either with commuters struggling against rain and wind at 7am. Picture: Nicholas Eager

Mr Funnell said rainfall up to 100mm daily was expected to hit the north coast today and tomorrow, before the weather system moves south. "At this stage, Sydney is looking at showers building through Thursday and Friday, with the heaviest falls on Saturday and Sunday."

State Emergency Services Deputy Commissioner Daniel Austin said volunteers were ready to help residents with the wild weather.