As the storms passed between 11am and 2pm, about 75,000 lightning strikes were detected within 100km of Sydney by Weatherzone’s Total Lightning Network.
The runway at Sydney Airport had earlier reached a near-standstill as more than 30 departures were cancelled and 340 services in and out were delayed.
Delays at times exceeded an hour for arriving flights.
More than 10,000 households and businesses lost power in the northern suburbs.
Network equipment damage at North Sydney meanwhile cut services from there to Gordon ahead of the afternoon peak.
Passengers were advised to delay their trip.
Sydneysiders had earlier been warned the thunderstorms passing over the city were likely to produce heavy rainfall in some areas, leading to possible flash flooding.
Particular areas of concern were the eastern and northern suburbs and areas north of Penrith and Colo Heights in the city’s outer west.
The warning was cancelled about 4.15pm as the storms moved into the central west.
Nearly 50mm fell in an hour at Kings Langley, in the city’s northwest, while another storm dumped 39mm within 60 minutes on Little Bay.
Near-stationary storms also caused downpours over Blacksmiths in Newcastle with 65mm falling in less than six hours.
The storms that hit Sydney caused a severe thunderstorm warning for areas near Orange, Mudgee and Bathurst.
A separate severe thunderstorm warning was in place for northern NSW ranging from Taree and Kempsey along the coast to Coonabarabran and Inverell inland.
