A severe thunderstorm warning has been issued for people in parts of the Blue Mountains/Hawkesbury, Sydney and Gosford/Wyong areas.
The Bureau of Meteorology warns that, at 3:15 pm, severe thunderstorms were detected on weather radar near the Wollemi National Park north of Kurrajong.
These thunderstorms are moving towards the east. They are forecast to affect Colo, Colo Heights and the Yengo National Park northwest of St Albans by 3:45 pm and St Albans, Maroota and Wisemans Ferry by 4:15 pm.
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Large hailstones and heavy rainfall that may lead to flash flooding are likely.
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 4:20 pm.
A more general severe thunderstorm warning is also current for parts of the Hunter, Metropolitan and Central Tablelands districts.