Another wet and stormy weekend is ahead for NSW with widespread rain and thunderstorms to batter much of the state.
The heaviest downpours of up to 200mm will hit the South Coast and Illawarra, prompting widespread flash flood warnings.
Sydney's Warragamba dam - already at 99 per cent capacity - is forecast to spill, bringing a flood threat to those downstream.
The water reservoir last spilled after heavy rain in April, causing catastrophic damage to some homes near the catchment area.
The Bureau of Meteorology's Sarah Scully said some coastal areas could receive anywhere between 50 and 100mm of rain on Friday night.
Some inland areas could be hit with isolated totals of between 50 and 70mm with thunderstorms predicted to increase the rate of rainfall and the risk of road closure.
However, the really heavy rainfall won't start until Saturday, with the rainband moving across to southeast NSW.
The potential for severe thunderstorms in the Sydney Metropolitan area and Illawarra will increase the risk of flash flooding.
Further south, rainfall totals of between 70 and 100mm are likely with the potential for up to 200mm in 24 hours.
The NSW State Emergency Service said heavy rainfall could cause the Hawkesbury River to flood, with isolated minor flooding in parts of the Hawkesbury Nepean Valley including North Richmond and surrounds.
A severe weather warning for heavy rainfall could also lead to flash flooding across northern parts of the South Coast, southern parts of the Illawarra and eastern parts of the Southern Tablelands from Saturday morning and into Sunday.
Wet weather is also forecast for neighbouring parts of Queensland and Victoria.
