The weather of Cusco can be divided into two particular seasons,
The dry season and the wet season.
The dry season accounts for May to September, while the wet season consists of the rest of the year (Oct-April).
The wet season- The wet season includes the months September to May. It rains throughout these seven months with an average rainfall of 152mm. Though it rains throughout the season, the middle portion of the season is considered to be comparatively damper.
The dry season- The dry season gets introduce in June and lasts till August. It is the best time to visit Cusco as you will experience only a minute rainfall (5-10mm), and the temperature is not even high. The average temperature stays around 16 degree Celsius.
Though this city is very calm and quiet, it gets very crowded during June and July due to the tourists. So if you want to enjoy the city in a calm and quiet way, it is suggested that you come on around May or August.