The Observatory said on Monday it would directly issue the Strong Wind Signal No. 3 at 5.20pm in place of the Strong Monsoon Signal as Tropical Storm Fengshen edges closer to Hong Kong.

"Under the combined effect of Fengshen and the monsoon, rain will be more frequent at times on Tuesday and early on Wednesday," the forecaster said on its website.

"It will be persistently windy in the next couple of days.

"Temperatures will fall appreciably to around 19 degrees in the urban areas, and a couple of degrees lower in the New Territories."

It noted that flooding may occur in some low-lying coastal areas because of the combined effects of the storm, the northeast monsoon and spring tide, noting that high tides are expected for a few straight nights this week.

The Observatory added that water levels in Victoria Harbour are expected to rise to around three metres above chart datum for three nights from Tuesday.

According to the weatherman, moderate to fresh northerly winds are expected on Monday, which are expected to be strong offshore and hit gale-force winds on high ground.