It came as the catchment received 87mm of rain in 48 hours.

In Sydney, 62 millimetres of rain was recorded at Observatory Hill in the 24 hours to 9am on Friday, but the highest falls were further south near Wollongong. More than 200 millimetres was recorded at Port Kembla.

The SES had issued 43 flood warnings as of 5pm on Friday, including eight telling residents to prepare to evacuate or isolate along the Hawkesbury and Nepean rivers.

SES crews have responded to more than 700 incidents over the past three days, including 474 in the 24 hours to 4pm – two-thirds of which were on the South Coast and in the Illawarra.

Spokesman Ben Deacon said there had been 39 rescues in the 24 hours to 4pm on Friday, mostly for people trapped in cars in floodwaters. A family in Warrawong, south of Wollongong, had to be rescued from the second storey of their home just before midnight after their first floor flooded and they watched their shed float away.

He said the SES was focusing on riverine flooding rather than flash-flooding.

“We’re playing very close attention to the Hawkesbury-Nepean valley. We have a series of flood warnings at different places along the river,” he said.

“A handful of properties, historical properties that were built beneath the one-in-a-100 flood line ... may be flooded, but no widespread impacts are expected.”

The bureau said the Nepean River at Penrith could reach about 6.2 metres on Friday evening, and the Hawkesbury may reach seven metres at Windsor overnight and into Saturday.

Moderate flooding was occurring on Friday along the Upper Nepean River, forcing the closure of the Menangle Bridge and prompting one motorist to abandon their car after it became trapped on a bridge.

Helicopter footage showed a NSW State Emergency Service volunteer checking the vehicle, which was almost entirely submerged.

The Yarramundi and Cattai bridges were also closed in the Hawkesbury-Nepean areas. South of Sydney, the Illawarra Highway was closed at Albion Park. Meanwhile, the Princes Highway south of Jervis Bay reopened after flooding closed the road in both directions. Other local roads across the state were closed due to flooding.

A spokesman for the Transport Management Centre warned people leaving Sydney for the long weekend to drive to conditions, which could change quickly, and to never drive into floodwaters. Motorists should also check for road closures on the Live Traffic app.

A severe weather warning issued by the Bureau of Meteorology advised heavy rain will continue in the Illawarra region and the south coast of NSW on Friday afternoon, as rain eases around Sydney.

As much as 100mm could fall in six hours in some areas, while others have already copped a drenching, the bureau warned.

Angus Hines, a senior meteorologist at the bureau, said the low pressure systems in the south-east of Australia were set to move away and take the rain with them on Saturday.

“Over the past couple of days some places around southern Sydney and in the Illawarra have seen 200 to 300mm, about two months’ worth of rainfall in less than three days,” he said.

“Because we did see that heavy rain, there are still likely to be some flood warnings in play as these river levels are running really high at the moment on the back of that rainfall.”