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Heaviest rain in 50 years for some

Humid and unstable north-easterly winds will continue through the week in Sydney with more thunderstorms expected on Thursday.

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The wet and wild weather that caused flooding in much of eastern NSW is likely to continue for much of this week.

Communities from Kempsey in the state's north to eastern suburbs of Sydney and Kiama south of Wollongong are assessing damage from heavy rain and strong wind over the weekend.

The Bureau of Meteorology examined the severe weather events, including whether a tornado hit Kiama, damagaing many houses.

Storm damage at Kiama. Image supplied by SES NSW.

Storm damage at Kiama. Image supplied by SES NSW.

‘‘While some damage appears to be associated with the very strong north/north-east winds funnelling around the local hills and headlands, there is also a narrow path of damage consistent with a tornado,’’ Julie Evans, senior meteorologist at the weather bureau, said.

‘‘Without visual observation of a funnel we cannot be conclusive, but it is highly likely that at least one tornado formed within that circulation," she said.

Josh Fisher, head meteorologist at Weatherzone, said the storm had the characteristics of a tornado from the radar observations: “It was a rotating storm over Kiama.”

Warragamba spills

The north-east corner of the state can expect 25-50mm of rain today, potentially complicating recovery efforts for some towns.

The Weather Bureau and State Emergency Service expect the heavily populated Nepean-Hawkesbury valley to Sydney's north and west will face minor flooding later today, in part because the giant Warragamba Dam has hit capacity and is automatically releasing water.

A spokeswoman for the Sydney Catchment Authority said the dam, which has spilled 53 times in its 53 years, will continue releasing water for several days. The dam's water total increased 6 per cent in the past week alone.

“When the water continues to rise 80mm above its full storage level, the central drum gates on the dam automatically open to let that floodwater through,” she said.

“If the water continues to rise to 230mm above that fall storage, (four) side radial gates start to open.”

The side radial gates were last open in March last year. The NSW government is reviewing flood risks for the Nepean-Hawkesbury valley and whether it should alter the dam's operating procedures to give it the power to release water earlier when flood risks intensify.

The rainfall outlook suggests inflows into the Warragamba will continue to be high for days to come.

“For the next days, we are going to see thunderstorms over parts of western Sydney,” Weatherzone's Mr Fisher said.

“These thunderstorms could impact the Warragamba Dam and the flows into that.

“There is the potential for another significant band of rain to move through on Thursday.”

Once in a decade - twice

The weekend’s storms also produced unusually high waves but the state's beaches again look likely to have avoided serious erosion, said Phil Watson, chief of the coastal unit at the Office of Environment.

The waves peaked on Saturday afternoon off Coffs Harbour with waves as high as 12.5 metres and significant wave heights averaging about seven metres - identical to recordings made in January after ex-tropical cyclone Oswald moved south.

‘‘That’s two events with an occurrence of a little over once in 10 years within a month,’’ Dr Watson said.

Waves off Byron were also at once-in-a-decade heights, with coastal damage from the storm reduced because the wave direction was south at the peak of the event.

"We’ve been quite fortunate with this event,’’ Dr Watson said. ‘‘Had it lasted a little longer and coincided with large tides then we would have expected quite significant erosion.’’

Insurers

Despite the widespread floods hitting towns including Kempsey, insurers are yet to declare the event a catastrophe based on current claims.

The industry has already declared catastrophes for floods three weeks ago stretching from central Queensland to the mid-NSW coast, and bushfires in Tasmania and NSW, with total claims approaching the $1 billion mark for summer.

Yarras, west of Port Macquarie, had the highest rainfall during the past week. It recorded 415mm in the 24 hours to 9am on Saturday, breaking a daily record for the area that had stood for 64 years, the bureau said.

Weatherzone is owned by Fairfax Media, publisher of this website.