September in Lạng Sơn averages a daily high of 30.1°C. Expect roughly 10.8 wet days totalling 153.4mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Lạng Sơn is October–December.
Based on LANG SON, VM (2.3km), 1995–2024. 20 years of September data.