A strong northeast monsoon would reach the coast of Guangdong later on Sunday, and it would be windy throughout the region over the next few days, it said.
A broad low pressure trough would bring unsettled weather to the central and northern parts of the South China Sea, with associated rainbands to cover the coast of Guangdong, it added.
Bright periods were expected on Sunday, with the temperature ranging between 25 and 29 degrees, while the following few days are forecast to be windy with a few rain patches.
Hong Kong had its hottest summer yet this year. The city recorded an average temperature of 29.7 degrees Celsius in August, the highest since records began almost 140 years ago.