Most expats enjoy Costa Rica's mild tropical climate and this is one reason it is very popular among retirees. Temperatures in the Central Valley (San Jose) only vary from 18 - 27 degrees Celsius (64-80 degrees F) during the year. Along the coastal areas, temperatures are higher, with the Caribbean side being slightly cooler at between 25 - 27 degrees C (77-80 degrees F) and the Pacific Coast being the hottest, averaging 31 -38 degrees C (88 -100 degrees F). Costa Rica only has 2 seasons, the rainy season ("winter") which runs from May to November and the dry season ("summer") from December to April. These seasons are relative, as each has a transition period and the sun often shines intensely in the mornings of the rainy season and thunderstorms are not unknown during the summer or "dry" season.

In addition, Costa Rica's geography creates "micro" climates, so the weather varies wildly, often from one town to the next, and often from one hour to the next as systems move through. The Caribbean Sea on one coast and the Pacific Ocean on the west coast bring weather systems, and rising up from the coastal plains are two mountain ranges that form the Central Valley, where most people live. This plateau is 1160 meters above sea level, but is bordered by mountains as high as 1500 meters on each side. The highest peak in the country is Mount Chirripo at 3819 meters. This rugged terrain and variable weather are responsible for the amazing number of plant, bird and animal species found in the country, about 6% of known species in the world.