The climate in Costa Rica is hot all year round in the plains and along the coasts, while it's milder in the plateau (in the so-called tierras templadas). In the Pacific coast and the plateau there's a dry season (from December to April), and a rainy season (May to November), in which rainfall is abundant, while in the eastern plain and coast the climate is equatorial, with abundant rainfall throughout the year.

Temperature variations are low, because the country is located near the Equator, so the main difference between the seasons is related to the rains. Anyway, most of the country is so rainy that it's covered by rainforests.

The capital city of San José is located in the central part, at 1,100 metres (3,600 feet) above sea level, on a plateau (the Central Valley, between the Cordillera Central and the Cordillera de Talamanca), thus it has pleasant temperatures throughout the year, with cool nights and warm days. In San José there is little rain from December to March, and it almost never rains in January and February. The rainy season runs from May to November, and the wettest months are September and October, with around 300 millimetres (12 inches) per month.

On the Pacific coast, the rainfall pattern is similar to that of San José and the plateau, although of course the temperature is higher. The Pacific coast is even slightly warmer than the Caribbean coast, especially in winter, when the north-east trade winds descend from the mountains and become hot and dry: the average daytime temperatures are around the 30/32 °C (86/90 °F) in the least hot period, from October to November, while they can reach 34/35 °C (93/95 °F) in March and April, before the rainy season.

The least rainy area of the country, where the savannah dominates, is the north-west (Province of Guanacaste), where the average rainfall drops to 1,300/1,500 mm (51/60 in) per year.

The east coast and the plain overlooking the Caribbean Sea (see Puerto Limón) is rain-soaked, and it receives more than 3,000 mm (118 in) per year; here the climate can be defined as equatorial, that is, without a dry seasons. However, there are two peaks in the rains, in July and December, both with about 440 mm (17.5 in) of rain per month, and two relative minima in September-October and February-March, both with about 150/200 mm (6/8 in) per month. In this area, December is even the wettest month, and January is wetter than February and March. South of this coast, on the mountain slopes of the Braulio Carrillo National Park, precipitation reach 5,000 mm (195 in) per year!

Along the coast of the Caribbean Sea, temperatures are a bit lower than on the Pacific coast, as the winds blow constantly from the sea, but for the same reason the humidity is higher.

At high altitude, above 2,000 meters, in the so-called tierras frìas, above 2,000 metres (6,600 feet), and even more on the slopes of the highest mountains and volcanoes, such as Cerro Chirripó, 3,820 metres (12,532 feet) high, or the volcano Irazú, 3,431 metres (11,257 feet), temperatures are low, especially in the winter months. Above 3,500 metres (11,500 ft), at night it can freeze throughout the year.

Costa Rica is almost always spared from hurricanes, whose path is usually located north of the country: in fact sometimes they can affect nearby Nicaragua; therefore the area most at risk is the northern one, which may be affected indirectly. The hurricane season runs from June to November (though they are most likely from August to October), during the rainy season, which in any case is generally not recommended for tourists.