Southwest China has subtropical temperatures toward the borders with Sichuan and Hunan, and Tropic of Cancer-like heat and humidity around the borders of Myanmar, Laos, and Vietnam.
Be sure to pack plenty of sunblock, spare pairs of socks, a windbreaker, hat, sunglasses, hiking boots, running shoes, and sandals.—yes, it's that diverse. Light cotton clothes are a good bet, but bring something warm if you're visiting the mountains.
In summer, the monsoons can be heavy. Keep abreast of weather reports on the Internet at any of the numerous cafés, hostels, and hotels.
The best time of year is spring, in April or early May. Winter months can be surprisingly cold (except on the south coast of Guangxi and Yunnan), and the summertime heat is stifling. Mid-September can also be a comfortable time to travel. The falls at Huangguoshu are at their best in the rainy season from May through October.