Source: Bureau of Meteorology

For people in parts of Blue Mountains/Hawkesbury, Gosford/Wyong and Sydney areas.

Issued at 8:44 am Friday, 17 January 2020.

The Bureau of Meteorology warns that, at 8:45 am, severe thunderstorms were detected on the weather radar near Hornsby and Terrey Hills. They are forecast to affect Parramatta and Glenorie by 9:15 am and Blacktown, Fairfield and Wisemans Ferry by 9:45 am.

Heavy rainfall that may lead to flash flooding is likely.

The State Emergency Service advises that people should:
* 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.