The observatory on Thursday said it will issue the Standby Signal Number 1 at 5.40pm.

The forecaster said a low-pressure area in the central to northern part of the South China Sea will soon develop into a tropical depression. It is expected to gradually move towards the coast of western Guangdong, near the Pearl River Estuary.

The observatory added that there will be squally showers and thunderstorms in the coming days, while winds offshore and on high ground will strengthen.