Planning for the weather is a good way to make your trip to Mong Cai relaxing and enjoyable, especially when you're splurging. The hottest months are usually July and June, with an average temperature of 28°C, while the coldest months are January and December, with an average of 17°C. The rainiest months in Mong Cai are August, July, June and September, with each month seeing an average of 339 mm of rainfall.