The observatory says it will issue the Standby Signal No 1 late on Thursday or early Friday, if Tropical Cyclone Trami follows its projected path and edges closer to Hong Kong.

"According to the present forecast, Trami to the east of the Philippines will intensify gradually and enter within 800 kilometres of Hong Kong," meteorologists said.

Trami, which is Vietnamese for a type of Camellia, is expected to move west towards the vicinity of Hainan in the coming days.

The observatory said a higher typhoon warning signal could eventually be possible, depending on the storm's movement and wind conditions.

Forecasters also warned that the weather will deteriorate this weekend.

"Under the combined effect of Trami and the northeast monsoon, it will be windy and become cloudy with a few showers over the coast of southern China later on Friday and over the weekend."