The observatory says it will issue the Standby Signal No 1 at 10.20pm on Saturday as yet another storm nears the city.

Just three days after the last No 1 signal was raised, a tropical depression has developed in the South China Sea and is threatening to bring rain and strong winds to Hong Kong.

"According to the present forecast, the tropical depression will move in the general direction of the vicinity of Hainan Island in the next couple of days... local winds will strengthen tomorrow (17 August)," the observatory said.

"Depending on its distance from Hong Kong and the change in local winds, the observatory will assess the need of issuing higher tropical cyclone warning signals later tomorrow morning."

Forecasters said Sunday will see showers and thunderstorms and with seas expected to be rough with swells, people should stay away from shorelines.

Some heavy showers will still be affecting the city on Monday and Tuesday, the observatory warned.