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Read more about this topic on the official site of the Instituto Meteorologico Nacional: Climate of Costa Rica - IMN.

December marks the start of the dry season. On the Pacific and Central side, the weather conditions are good, but the first weeks can bring you some remainders of the rainy season. The Caribbean side however endures a lot of rain, focusing on the Northern part. Tourism is still on a low in the beginning of December, but this will explode in the last weeks of December when the schools are closing and the Christmas and New Year tourism starts to take off. Schools are closed in Costa Rica during January. The Pacific and Central regions of the country experience good weather conditions with little rain. Guanacaste is relatively the driest and hottest region. The Caribbean side however experiences heavy rains in the North to moderate rains in the South that can last days. In February the peak season is over but due to the weather conditions it is a high season month. The Weather conditions in February are similar to January, although the changes of heavy rains on the Caribbean side is decreasing. March is the second high season month. The Pacific and Central regions are almost without rain, and it is the hottest month in Costa Rica, focusing on Guanacaste. The Caribbean side is cooler than the pacific side and experiences rainfall most afternoons.

April is still a relatively dry month in the entire country while the weather is slowly transiting to the rainy season causing some afternoon or evening rains. Semana Santa or Easter week is an important vacation week for Ticos which is pushing the high season forward. Being collectively free, it can be crowded at beaches and national parks and public transport can be limited in some areas. During May, the rainy season is really starting to push through, and the high season has come to an end. The amount of rain is increasing, but it is not raining every day. Nature is beautiful after the first serious rainfall in the drier regions.  During June, tourism remains on a low while the entire country is experiencing rainy days. While this is usually during the afternoon or evening, the Caribbean side might experience some full days of rain, which increase in July.  The Pacific and Central regions of the country continue experiencing dry mornings, with rains in the afternoon or evening. Focusing on Guanacaste there is a noticeable drier period during July and the beginning of August schools in Costa Rica have a two-week vacation period and combined with school vacations in western countries this is causing an increase in tourism which lasts until August. Rains on the Caribbean side are getting less and sunny days with little rain are starting to appear.

September through November is low season in Costa Rica. Rainfall on the Pacific and Central side of the country is increasing in September, although most mornings still allow sunshine. The South Pacific however experiences the most rain which can go on continuously for days. September and October are not good months to visit the Osa Peninsula, while certain parts of Corcovado together with tours and hotels are limited. The contrast with the Caribbean side could not be bigger, where September and October are relatively nice and sunny. During November the weather is still rainy but starting to improve. It’s a transit month between a period of heavy rainfall and the start of the dry season in December. Early November, the Osa Peninsula still endures a lot of rain. During November, the sunny period ends for the Northern part of the Caribbean, while the Southern part still has nice weather.

El Niño and La Niña are two natural weather patterns that occur periodically and have a significant impact on climate and weather patterns around the world, including in Costa Rica. El Niño refers to a warming of the waters in the Pacific Ocean. In Costa Rica, El Niño is associated with drought conditions and a reduction in rainfall on the Pacific side, but increased rainfall on the Caribbean side. During an El Niño year, Costa Rica can experience higher temperatures and reduced agricultural productivity. La Niña, on the other hand, refers to a cooling of the waters in the Pacific Ocean. In Costa Rica, La Niña is associated with increased rainfall and a greater risk of flooding and landslides, and increased agricultural productivity. The El Niño and La Niña phenomenon is hard to predict, but are usually followed by each other, occurring every 2 to 7 years. Read more about this topic on the official site of the Instituto Meteorologico Nacional: ENSO - IMN.

Finding a weather app or a forecast for Costa Rica that gives a good indication of the expected weather conditions can be hard. Regional weather forecasts and weather warnings can be found on the website of Instituto Meteorologico Nacional. The forecast provides an overview per region during different parts of the day.