Update
Motorists are being urged to take care after heavy rains caused flash flooding in St George and Sutherland Shire today.
NSW State Emergency Service (SES) Kogarah unit today implored motorists to never drive, ride or walk through floodwater.
"Kogarah Unit was attending flooding south-bound on Princes Highway at Kogarah Bay this morning and our members were horrified at people driving in front of an emergency vehicle straight into the water they were blocking the public from," the unit posted on its Facebook page.
"Thankfully, no one was injured this time but there were some close calls.
"With further rain expected, please drive to the road conditions and if you see an emergency service vehicle displaying lights please slow down to 40km/hr (in suburban areas)."
Update
Good rainfall has fallen in St George and Sutherland Shire overnight and this morning, with almost 60 millimetres of rain recorded in the Royal National Park.
While predicted thunderstorms and heavy rain failed to materialise yesterday afternoon, the rain finally came early this morning, with Sutherland Shire receiving the most rainfall.
Bureau of Meteorology Sydney rainfall figures show the Royal National Park recorded 59mm of rain in the 24 hours to 9am today, while Cronulla recorded 40mm.
In St George, Peakhurst monitoring station recorded the biggest rainfall, with 43mm, followed by Sydney Airport with 32mm and Sans Souci, which recorded 26mm.
The rain brought flash flooding, with two northbound lanes of Rocky Point Road at Sans Souci under water during today's morning commute, causing long delays for motorists, with traffic stretching back over Captain Cook Bridge and into Taren Point.
Earlier
St George and Sutherland Shire commuters reached for their brollies for the first time in weeks this morning as thunderstorms brought welcome rain, with more predicted in coming days.
And the rain couldn't have come at a better time as Sydney dams reach worrying levels.
Motorists are being warned to take care on the roads this afternoon after the Bureau of Meteorology issued a Sydney Road Weather Alert at 12.10pm following predictions of heavy rain.
"Slippery roads and reduced visibility in heavy rain with thunderstorms may make driving conditions dangerous later Thursday afternoon and evening in all suburbs," the alert said.
"Motorists are advised to take extreme care."
"We are expecting heavy falls to cause flash flooding. Try not to park your car under a tree [because] with this rain after so much dry weather we are expecting a large number of branches to fall and most importantly, please don't drive through floodwater," Sutherland Shire SES warned.
Almost a millimetre of rain fell at Lucas Heights since 9am today while Sydney Airport recorded 0.2mm. No rain was recorded at Kurnell.
A Bureau of Meteorology rainfall outlook for January 13-19 predicted a wetter than average week across much of the north and west of the continent as well as southwest Queensland and northern NSW.
Sydney's forecast for the rest of today is possible thunderstorms this afternoon and evening with the possibility of bringing heavy rain.
The maximum temperature is 26 degrees, falling to a maximum tomorrow of 23 degrees, when more rain is predicted with possible storms.
Saturday and Sunday are also likely to bring rain, with a chance of more thunderstorms both days, and a possible storm on Monday before a return to warmer, drier weather on Tuesday.
Woronora Dam levels are currently at 34.6 per cent capacity - the second lowest in the Sydney catchment, which is at 43.2 per cent. Only Cataract Dam near Appin is lower, at 25.6 per cent capacity.
