“Under its influence, the weather will become unsettled gradually over later parts of this week,” it said.
More rain is forecast from Thursday through to Monday the following week, but temperatures will remain hot at about 32 degrees Celsius (89.6 Fahrenheit).
The Observatory warned last week that three to five more typhoons could enter within 500km (310 miles) of Hong Kong this year.
Only five typhoons formed in the northwest Pacific and South China Sea during the first seven months of the year, about half the long-term average of roughly 10.
