SEVERE THUNDERSTORM WARNING for LARGE HAILSTONES and FLASH FLOODING

For people in the Metropolitan, Illawarra and parts of the Northern Rivers, South Coast, Central Tablelands, Southern Tablelands, Snowy Mountains and Northern Tablelands Forecast Districts.

Severe thunderstorms are likely to produce large hailstones, very heavy rainfall and flash flooding in the warning area over the next several hours. Locations which may be affected include Lismore, Penrith, Parramatta, Nowra, Bowral and Katoomba.

The State Emergency Service advises that people should:

* Move your car under cover.

* Keep clear of creeks and storm drains.

* Don't walk, ride your bike or drive through flood water.

* If you are trapped by flash flooding, seek refuge in the highest available place and ring 000 if you need rescue.

* Unplug computers and appliances.

* Avoid using the phone during the storm.

* Stay indoors away from windows, and keep children and pets indoors as well.

* For emergency help in floods and storms, ring the SES (NSW and ACT) on 132 500.

The next warning is due to be issued by 6:15 pm.

If severe thunderstorms develop in Sydney Newcastle Wollongong or surrounding areas, a more detailed Severe Thunderstorm Warning will be issued to people in this area.

Warnings are also available through TV and Radio broadcasts, the Bureau's website at www.bom.gov.au or call 1300 659 218. The Bureau and State Emergency Service would appreciate warnings being broadcast regularly.