Flash flooding inundated major roads in Strathfield, Bexley and the Blue Mountains and residential streets across the city after the Bureau of Meteorology issued a severe thunderstorm warning for a wide area of central and eastern NSW, extending to the Sydney Metropolitan region. (See chart below.)

Peter Zmijewski, a senior bureau forecaster, said the storms were likely to continue for the next couple of hours: "There are quite a few cells."

For the Sydney region, the bureau updated its detailed warning just before 6pm to state that while severe thunderstorms in the warning area had temporarily eased, "further severe thunderstorms are still possible".

Trains from the city to Lidcombe terminated at Sydenham, with flooding at Marrickville Station, while "urgent repairs" were being carried out on train signal equipment at Hurlstone Park.

The weather also affected power, with 4800 homes left in the dark in the Blue Mountains and western Sydney after lightning strikes hit transmission lines in the Blue Mountains.

Endeavour Energy said all customers in Blackheath and Springwood had their power cut for approximately five minutes.

Power remains out in parts of Wentworth Falls, Leura and Valley Heights, where 2500 people are affected, in parts of Penrith between Llandilo and Jordan Springs, and in Mount Druitt and Rooty Hill.

Locations across the state that may be affected by the storms include Sydney, Wollongong, Orange, Mudgee, Bathurst, Katoomba, Walgett, Dubbo, Parkes, Cobar, Bourke and Lightning Ridge, the bureau said.

Mr Zmijewski said conditions are again likely to favour storms across Sydney on Wednesday afternoon.

On current forecasts, the bureau is expecting 8-15 millimetres of rain on Wednesday.

"There's a high chance for showers each day" up until about the weekend, said Graeme Brittain, a Weatherzone meteorologist.

"We've had these moist on-shore flows, and above-average sea surface temperatures off the NSW coast," Mr Brittain said.

The additional moisture that's available has combined with upper-level pools of cool air to create ongoing instability and rain.

While nights have been exceptionally warm, the clouds are keeping a lid on temperatures - although most days are above the March average.

"There's no real sign of any real heat making it towards the coast over the next week or so," Mr Brittain said.

Still, there's a chance for some reasonable sunshine on Sunday and early next week, as temperatures in the city climb back towards 30 degrees.

So far in March, Sydney has had 18 days with at least 0.2 millimetres of rain, or well above the average of 13.6 rainy days for March, according to Agata Imielska, senior climatologist with the bureau in Sydney.

The record of 26 rainy days, set in 1870, is perhaps out of reach but the 22 wet days in March 2014 is within reach.

In terms of rain totals, the 223 millimetres - before Tuesday's falls - is already well above the average of 129.6 millimetres for March at Observatory Hill.

"The record March total is 521.4 millimetres in 1942, so we've got a way to go to reach that record as well," Ms Imielska said.

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