🇨🇷Costa Rica

Costa Rica lies between 8°02′ and 11°13′N as a narrow Central American isthmus straddling the continental divide between the Caribbean and Pacific oceans. A central volcanic cordillera reaches 3,820 m at Cerro Chirripó, with major active stratovolcanoes including Arenal, Poás, Irazú, and Turrialba, producing a steep elevational and rain-shadow gradient.

The humid tropical Af climate dominates the perpetually wet Caribbean slope around Limón and Tortuguero, while the tropical monsoon Am characterizes the southern Pacific Osa peninsula. The dry northern Pacific Guanacaste region exhibits tropical savanna Aw conditions, the Central Valley around San José and Heredia at 1,100 to 1,500 m enjoys an oceanic temperate Cfb or Cfa climate, and high-altitude Cwb and páramo conditions prevail above 3,000 m on Cerros de la Muerte.

San José at 1,170 m averages a balmy 20°C year-round with 1,900 mm concentrated in a marked wet season from May through November. Limón on the Caribbean coast receives 3,500 mm with no dry season, while Quepos on the Pacific experiences 23°C with 4,000 mm annually. Liberia in dry Guanacaste averages 28°C with 1,650 mm and a sharp dry season from December to April.

Cerro Chirripó has frosty conditions with occasional sub-freezing temperatures and very wet conditions exceeding 5,000 mm. The Caribbean trade winds, Pacific ITCZ migration, and the Caribbean low-level jet drive rainfall patterns, including the Veranillo mid-summer drought in July.

ENSO oscillations drive huge interannual swings, with strong El Niño events causing Pacific droughts as in 2015, and strong La Niña events bringing Caribbean flooding such as Tropical Storm Nate in 2017. Coastal erosion and coral bleaching pose serious threats, and major recent events include the 1991 Limón earthquake-tsunami and recurrent Turrialba ash falls.

Our archive covers 1 Costa Rican cities with daily ERA5 reanalysis data going back to 1940. The warmest July averages occur in San José, around 24.3°C, while San José records the coldest January nights near 15.9°C. Comparing the last decade against the 1940–1970 baseline, mean temperatures across these cities have risen by about 0.9°C.