Australia Weather News

The storm can be seen brewing at the foot of the Blue Mountains. - ABC

A severe thunderstorm warning issued for heavy rainfall and large hailstones has been downgraded for parts of Sydney and New South Wales.

The Bureau of Meteorology (BOM) warning previously included the Illawarra, Sydney metropolitan, South Coast, Central Tablelands, Southern Tablelands and Snowy Mountains areas.

Earlier, BOM forecaster Jordan Notara said several large storm cells were being monitored.

"From radar imagery we are seeing that the signature from that is suggesting that there is the potential for large hailstones in that cell," he said.

"That interaction between the easterlies and the general westerlies from above create good instability and a lifting mechanism that initiates storms within that area."

Mr Notara said more storm activity was expected for about a week.

"We should be seeing generally these sort of conditions becoming more of a trend over the coming days and we are seeing a forecast for potential storms at least for the next seven days," he said.

The State Emergency Service (SES) warned residents to move cars undercover or away from trees, secure loose items in gardens, balconies or yards, and keep away from fallen powerlines.

The SES asked that people avoid using phones during a storm and keep children and pets indoors.

ABC