The climate of Sapa is highly seasonal, with a subtropical climate in the summer and a temperate climate during the winter. Average temperature for Sapa town is 15.4ºC, with a maximum of 29.4ºC and a minimum of 1ºC.
Sapa also experiences a marked wet season from May to September, with the heaviest rainfall occurring in July and August. The weather is also notorious for changing frequently and quickly.
It is said that only in Sapa, one can experience many different seasons within only one day.
The climate of Hoang Lien Nature Reserve 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 Nature Reserve experiences a marked wet season from May to September, with the heaviest rainfall occurring in July and August. Mean annual rainfall is 2,763 mm, 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 nature reserve. 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 nature reserve, around Ban Ho village, mean temperatures are considerably higher due to the lower altitude of these areas.