Yunnan Weather in September

In short: neither too cold nor too hot, moderate rainfall
 

Tiger Leaping Gorge in September

 In September, Yunnan enters autumn and the temperature in most parts begins to drop but only a little. Places including Kunming, Lijiang, and Dali enjoy mild weather, with the average maximum temperature from 20 - 25°C (68 - 77°F). At night, the temperature may drop below 15°C (59°F), so you are advised to wear an additional thin jacket. In high-altitude areas like Shangri-La, the overall weather is cool, and the high temperature is no more than 20°C (60°F). However, in southern areas like Xishuangbanna and Honghe, you may still feel a little hot; in the midday hours, the temperature is above 30°C (86°F), not suitable for outdoor activities.
 Though September is still the rainy season in Yunnan, its rainfall drops to a relatively moderate level. Some cities such as Lijiang, Dali, and Xishuangbanna have an average rainfall of around 150 mm, while Kunming, Shangri-La, and Honghe have an average rainfall of around 100 mm. Except for Xishuangbanna where the average number of rainy days is 10, most cities have around 20 rainy days. Therefore, the average daily rainfall is not very much, and the rain in Yunnan is usually not continuous and long-lasting.
 The daylight hours also begin to shorten this month, which is about 12 on average. With the influence of moderate rainfall, the sunshine hours are short at about 5 hours daily on average. Therefore, you are advised to better arrange your itinerary based on the weather condition.