If you’re looking forward to lots of outings with your partner, take a look at these details about year-round temperatures in Jiangmen: The hottest months are usually July and August, with an average temperature of 29°C, while the coldest months are January and December, with an average of 18°C. The rainiest months in Jiangmen are June, August, May and September, with each month seeing an average of 294 mm of rainfall.