A severe weather warning for damaging winds, heavy rainfall and damaging surf was cancelled at 10pm on Wednesday.

An evacuation warning was issued for areas downstream of Jerrara Dam, near Kiama, after the storage reached an "amber alert" level on Wednesday, while elsewhere roads were flooded and others covered in sand.

On Tuesday night, police evacuated an 80-year-old woman from her home on Cathedral Rocks Avenue at Kiama Downs due to fears of a potential landslide.

Conditions were at their worst on Tuesday night, with 81.8 millimetres of rain dumped on Bellambi Point and 67.6 millimetres registered in the Albion Park gauge in the 24 hours to 9am Wednesday.

Weatherzone meteorologist Ben McBurney said southern parts of the Illawarra would be the wettest on Wednesday night and into Thursday, but conditions would eventually ease.

The most severe conditions associated with the east coast low peaked on Wednesday afternoon and were expected to ease further as the low weakened.

"In terms of rainfall, probably another 20 to 50 millimetres is likely to fall in the next 24 hours across the Illawarra," Mr McBurney said late on Wednesday. "We should start seeing fairly rapid easing from [Thursday] and by the end of the week we should see mostly dry conditions with only a few light showers around the place.

"The broader low itself is off the Illawarra now, but compared to [Tuesday] and Monday afternoon the low has really weakened substantially. We still have the risk of heavy showers particularly [Wednesday] evening and into [Thursday] morning but as the afternoon wears on ... it should really be improving a lot."

NSW SES Deputy Commissioner Steven Pearce said the organisation was preparing itself for the tail end of the system.

"The storm basically started here in the Illawarra and moved north and now it's returning again, so for the next 24 hours the Illawarra and the South Coast should brace themselves for the onslaught of some very challenging weather - high, gusty winds up to 100km/h, rainfall in patches of up to 100 millimetres an hour," Mr Pearce said mid-afternoon Wednesday.

"So again people just need to be cognisant of making their travel plans and please under no circumstances should they try and drive, walk or drive through floodwaters."

By late Wednesday, the SES had received 11,003 calls for assistance statewide since the weather event began, with about 325 jobs coming from the Illawarra.

Mr Pearce described the overall storm operation as one of the most challenging the SES had been involved with in the past 10 years. "East coast lows historically ... come in, they hit hard and they leave very quickly," he said.

"This one has been a complete anomaly, it has come in and it's stayed in place and it's stayed with the same intensity."