Since Costa Rica is located well within the Tropics of Capricorn and Cancer, its climate by definition is tropical. This means it only has two seasons: a dry season with little to no rain — depending on the area, and a rainy season (also called green season), when it rains continuously.

Monteverde Cloud Forest, North Region - photo by redwood-dragonCosta Rica's tropical weather is modified by different components like topography (the layout of the mountains, flat lands and plateaus), the ocean's influence (winds, sea breeze, the currents' temperatures, etc.), and the general circulation of the atmosphere.

Costa Rica has a northwest–southeast orientation and this effectively divides the country in two main zones: the Pacific and the Caribbean. Each zone has its own characteristics with particularities arising from the topography.

The Pacific

This zone possesses very defined seasons. The dry season goes from December to March, with the driest and hottest month being March. April is considered a transition month.

The beginning of the dry season depends on the location of the zone: it usually begins in the northwest territory first and then reaches the southwest of the country. The contrary happens during the rainy season.

Tortuguero Canals, North Caribbean - photo by redwood-dragonThe rainy season goes from May to October. November is a transition month. It rains usually in the afternoon or during the first hours after sundown. September and October are the most rainy months.

The Caribbean

In this region there is not a very defined dry season, since it still rains considerably (an average of 100 to 200 mm) during the less rainy months.

There are two drier periods on zones close to the coast. The first goes from February to March and the second from September to October. The first period is in synch with the Pacific section one but the second actually corresponds to the rainiest period in the Pacific. Rains occur with more probability at night and in the mornings.

Micro–climates

Due to factors like height, mountain orientation, winds, and the influence of the two oceans among other variables, the country has 7 main weather zones in an area of 51,100 km² (roughly one third of the State of New York): North Pacific, South Pacific, Central Pacific, Central, North, North Caribbean, and South Caribbean.

Although Cartago province belongs to the Central zone, it lies towards the east in the Oriental Valley, which is higher than the Occidental one where San José province is. It rains less in the Oriental Valley but more frequently and temperatures do not go as high as well. According to the Insituto Metereológico Nacional (the Costa Rican Meteorological Institute) there can be up to a 5 °C (9 F) difference between both valleys in their maximum and minimum temperatures. Cartago city in particular has long been referred to as the «Misty or Foggy City.»