Threat Level AMBERFor people in parts of the Sydney area.Issued at 10:09 am Wednesday, 16 December 2015.The Bureau of Meteorology warns that, at 10:10 am, very dangerous thunderstorms were detected on weather radar near Bundeena and the Royal National Park. These thunderstorms are moving towards the north. Very dangerous thunderstorms are forecast to affect Sutherland, Sydney Airport and waters off Bondi Beach by 10:40 am and Sydney City, Sydney Olympic Park and the Sydney Harbour Bridge by 11:10 am.Destructive winds, large hailstones and heavy rainfall that may lead to flash flooding are likely.Wind gust of 91 km/h at Bellambi Point at 915am.The State Emergency Service advises that people should:* Move your car under cover or away from trees.* Secure or put away loose items around your house, yard and balcony.* Keep clear of fallen power lines.* 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.