Costa Rica is indisputably a tropical country, positioned between 8° and 11° North latitude, moderately close to the equator. Although in the mountains above 2000 meters much cooler temperatures prevail, the average annual temperature for most of the country lies between 21.7°C (71°F) and 27°C (81°F). The coolest months are from November through January, and the warmest from March through May. San José, the capital; where over a third of the population lives, stands at approximately 1170 meters altitude and has a mean annual temperature of 20.6°C.

The climate of Costa Rica is typically divided into two major seasons: rainy and dry. The dry season runs from January through May and the rainy season from May to November and December. Locally, the seasons were named by the early Spanish colonizers, who compared them to their own Mediterranean climate, calling the dry months "verano”, or summer, and the rainy, grey and gloomy months "invierno" or winter.

Rainfall patterns, although seasonal, vary deeply in intensity across geographical areas. Some locations receive over 6 mts (18 ft) of rainfall per year, while others receive fewer than 1.5 mts (4 ft). Most of the total rainfall for any given site (about 70%) occurs on less than 15 days of a whole year, and will often be experienced as days of torrential downpour. Costa Rica may hold the world record for the amount of rainy days at one site.

The topography of the country also has a great authority on the weather patterns of a given locality. As a result the timing of the dry and rainy seasons varies a bit on each slope of the mountain ranges that run from the north-west to the south-east and divide the nation into a Caribbean slope and a Pacific slope.