The Observatory is considering raising a T1 storm signal on Tuesday, after an area of low pressure southeast of Hong Kong intensified into a tropical depression.
The storm is expected to move across the northern part of the South China Sea over the course of Monday.
At 12pm on Monday, the tropical depression with maximum sustained winds of about 45 kilometres per hour was located northeast of the city.
The storm is forecast to move across the Luzon Strait slowly at first, and move west at about 12 kilometres per hour before entering the northern part of the South China Sea later.
There will be isolated showers on Monday with temperatures reaching 27 degrees Celsius. This will be followed by sunny periods with some haze on Tuesday, with temperatures reaching a maximum of 31 degrees Celsius. Occasional showers are forecast throughout the week, with very hot weather expected on Wednesday.