The observatory said on Thursday that it expects to keep the Standby Signal No 1 in place for the rest of the day, with Severe Typhoon Koinu continuing to keep its distance from Hong Kong.

Its present track suggested Koinu would maintain a distance of about 500 kilometres or more from the SAR on Thursday before moving closer to the territory over the weekend.

The observatory said the effect of the northeast monsoon is likely to weaken the intensity of the storm as it comes near and it's not certain whether a higher storm signal will be required.

"Under the influence of drier and cooler air of the monsoon, it will weaken gradually. The need for issuance of higher tropical cyclone warning signals depends on how fast Koinu weakens and its distance from the Pearl River Estuary," said acting senior scientific officer Kok Mang-hin.

Showers and strong winds are expected over the weekend and on Monday.

The No 1 signal was issued at 9.40pm on Wednesday.