Emergency services are on high alert as another super-cell storm is tipped to cut a swathe across New South Wales and affect Sydney later today.
Major thunderstorms - many of them severe - have hit most of the state since the beginning of the week and emergency services are bracing themselves for another busy day.
There were about 300 emergency callouts across NSW last night, with a likelihood of severe storms right down the state's coast.
"We're just preparing for different levels of those thunderstorms to hit across the mid to eastern parts of the state," SES spokesman Todd Burns said.
The SES urged people to avoid floodwaters and to secure loose items around their homes ahead of the forecast storm due to hit late today.
Photo: Storm clouds roll over Sydney Harbour (Twitter: SquiggleV)
Weather forecasters said the line of thunderstorms, caused by slow-moving low pressure troughs, are expected to ease on Sunday but will linger until at least the middle of next week.
The Bureau of Meteorology issued a severe weather warning for heavy rainfall for the Illawarra, South Coast, Southern Tablelands and Snowy Mountains districts.
Spokesman Francois Geffroy said the heavy showers forecast could lead to flash flooding. At 10:40am (AEDT), 35mm of rain was recorded at Currajong, near Jervis Bay.
"There's a slow-moving trough over inland NSW, sucking in moist and unstable air over the last few days, resulting in storms and thunderstorms over much of the state, except for the far north-west," Mr Geffroy said.
Photo: A massive storm cell moves over Pittwater on Sydney's northern beaches. (Supplied: Helen Hayes, Facebook)
"An upper trough will intensify the amount of rain expected over the south east of the state and severe weather warnings could be issued for parts of the south coast," he said.
"Yesterday there were falls of over 50 millimetres in some areas including the northern rivers, the Illawarra and the south coast and Wollongong had 66 millimetres [on Friday]."
Thunderstorms rolled across the state on Friday, bringing lightning, rain, flash flooding and hail to the Blue Mountains and western Sydney.
On Friday, one lightning strike started a fire at a kiosk at Rooty Hill in Sydney's west while Asquith Public School was hit by lightning as about 400 people gathered for a Christmas carols show.
About 6,000 customers lost power, although most had it restored by late evening.
Just after the height of the storm, Fire and Rescue New South Wales received 40 calls for help.
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Storm preparation advice:
* Maintain your yard and balcony, and secure or store items that could blow around in strong winds
* Clean your gutters, downpipes and drains regularly to prevent blockages
* Trim trees and branches that could potentially fall on your home or property
* Prepare an emergency kit with essential items in case you lose power or need to leave home in an emergency
* Make a Home Emergency Plan for your family that outlines what you would do in an emergency
* Listen to your local radio station for weather warnings
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