The lowlands of Costa Rica harbor a tropical and subtropical climate while the highlands experience a mountainous climate. The interactions between the trade winds from the east and the region’s topographic diversity creates a "rain shadow" effect, with the Caribbean slope experiencing rain practically all year round and the Pacific slope characterized by a prolonged dry season lasting approximately from November until April or May and a wet season during the rest of the year. The increased intensity of the trade winds in July produces a peak of precipitation on the Caribbean slope. Daily temperatures reach their maximum value before the start of the rainy season. Minimum temperatures show a different pattern, with the highest values observed in July and the lowest values during the Northern Hemisphere winter.
- Temperatures have increased between 0.2°C and 0.3°C per decade with a prolonged and hotter dry season since 1960.
- Between 1961 and 2003, the number of warm days increased by 2.5 percent and nights by 1.7 percent, while the number of cold nights and cold days decreased by 2.2 and 2.4 percent per decade.
- Temperature extremes increased by between 0.2°C and 0.3°C per decade since 1960.
- While most climate data show positive trends (increased precipitation), overall average annual precipitation in the region and the number of consecutive wet days do not show significant changes although there has been a slight increase in intensity.
- Extreme precipitation has increased significantly since 1960 and is strongly correlated with the temperature of the tropical Atlantic Ocean. The latter indicates that prolonged rainy seasons are related to the warm waters in that oceanic basin.
- The trend over the last 40 years suggests a strengthening of the hydrological cycle, with more intense rain occurring during shorter periods of time that produce greater average precipitation per episode. This trend is expected to continue in the future due to climate change, possibly resulting in a greater frequency or intensity of extreme events such as floods and droughts.
This section provides the options to visualize historical climate data for different timeframes via map and annual cycle chart.