Photos | Homes flooded, motorists trapped after storm cells collide over shire

The shire and St George received some of the biggest downpours across Sydney.

Bureau of Meteorology figures for the 24 hours to 9am on Saturday, recorded by fixed rainfall gauges, included Peakhurst (157mm), Lucas Heights (156mm), Royal National Park (152mm), Sydney Airport (145mm), Cronulla South (140mm) and Sans Souci (130mm).

Sutherland Shire SES received 104 requests for assistance since Friday morning, of which 45 were storm related and the remainder involving flood assistance.

The SES response was provided by five teams of volunteers in the field, plus an incident management team working from the Heathcote control room.

Inspector Daryl Brett, the SES unit commander for Menai, who was the shire-wide commander for the weather event, said the flood related incidents included vehicles driving through floodwater with people becoming trapped, and a relatively large number of properties unable to to cope with the volume of water.

"Looking at the radar, about 4am today, two cells merged right over the top of us, which affected the whole of Sutherland Shire," he said.

"Pretty much no road was left untouched."

Inspector Brett said, of the 104 requests for assistance, about half were "storm related - trees on cars, trees on houses, collapsed walls, landslides, all the things you associated with wet weather and strong winds."

Inspector Brett said the volume of water that fell between 4am and just after 5am inundated water systems.

"Unfortunately the weather event also coincided with the high tide, so it was just enough to break the banks of the Woronora River and inundate some properties at Woronora.

[In past similar events, stormwater has burst out of drains along roads and flowed into properties from the rear].

"The volume of water also automatically activated an evacuation alert for low lying areas of Bonnet Bay.

"It was just a preparatory measure, but it was very short-lived and no actual evacuations took place."