The best season to visit Costa Rica is generally the dry "high" season, which runs from mid-November to April, as the amount of rainfall during the rainy "green" season, which runs from April to mid-November, can make some roads impassable. December and January are particularly good months to visit, as the countryside is still green from the rains and the skies are more likely to remain clear.
Costa Rica is a tropical country, but temperatures vary according to the region and elevation rather than the season. The mountains can be very cool at night throughout the year, while the coast remains hot year-round. The country's Caribbean coast, particularly the area south of Limón, can be rainy, hot and humid throughout the year, but it experiences less rain than many other areas in September and October. Pacific storms from August to October can bring swells to the country's Pacific coast, making the area popular with surfers at this time of year. September and October are the best months to get a clear view of the active Arenal Volcano.
Guanacaste Province, located in the northwest region of the country, has a longer dry season that extends into May. During the rainy season, the rainfall often holds off until the afternoon, leaving the mornings sunny.