The climate of Hoang Lien National Park is unique to Vietnam. It is highly seasonal, with a subtropical climate in the summer and a temperate climate during the winter.
Mean annual temperature for Sa Pa town is 15.4°C, with a maximum of 29.4°C and a minimum of 1°C. The warmest months are July and August, and the coldest months are December and January. Snow falls in some years on the highest peaks.
In common with the rest of northern Vietnam, Hoang Lien National Park experiences a marked wet season from May to September, with the heaviest rainfall occurring in July and August. Mean annual rainfall is 2,763mm, with a high of 4,023mm and a low of 2,064mm. Humidity ranges from 75 to 91 percent with a yearly mean of 86 percent.
Climate varies considerably within the national park. The prevalent wind direction for most of the year is west to east, leading to cloud formation on the upper slopes of the Fansipan massif. These high-altitude areas are covered by cloud most days of the year and have very high humidity. Cloud also penetrates into the valleys but these areas are usually less humid than the mountain slopes. In the extreme east of the national park, around Ban Ho village, mean temperatures are considerably higher due to the lower altitude of these areas.