DUNGOG has been deluged with a one-in-100-year rain event, according to Weatherzone senior meteorologist Rob Sharpe.
More than 260 millimetres hit Dungog across a 32 hour period earlier in the week.
The Paterson and Williams Rivers peaked at 16 metres at Gostwyck Bridge, Dungog, at 4pm on Tuesday afternoon.
Mr Sharpe said it was the heaviest falls in the past 100 years.
The weather system developed from a low pressure trough of warm, moist air on the NSW coast, which combined with cold upper level air which had moved across from inland NSW.
The system, called an east coast low, is common in autumn, but rarely reached this magnitude, Mr Sharpe said.
"This is one of the strongest systems in the past decade.
"Winds in the Hunter reached 135 kilometres an hour; that's the strongest they've seen since 2007 when the Pasha Bulker (cargo ship) got stranded (on Nobbys Beach in Newcastle)."
The system produced winds equivalent to a category one tropical cyclone, and at times a category two.
Trangie and Coonabarabran both received the heaviest rain its had in two years but the storm's impacts tapered off further west, leaving some of the driest parts of the state exactly as they were."
Dairy farmer Danny Ernst, from Clydedale via Singleton, said this flood differed dramatically from the Hunter's past event in 2007 because the latter was caused by bulging rivers as water from further north and north-west inundated the Lower Hunter.
"It wasn't a lot of rainfall then, but a lot of water from upstream so at least we don't have to contend with that now as well," he said.
"Usually you would only see this when it's backed up from a flood - but there's been so much rain."
Ironically, his father, retired dairyman Peter Ernst, had been haranguing him about getting a part for his centre pivot - which now sits among drowned lucerne in about 80cm of water.
"Somehow I don't think that getting that part I need for irrigation is an urgent necessity," Mr Ernst told his father on Wednesday morning.
