You will find the best weather in Costa Rica during the dry season from December to May. You will likewise find the most people visiting the country during this time as well. However, the busiest times are during winter holidays when all of the world comes to Costa Rica to escape the cold and lay out on the beautiful beaches.
Though the dry season is from December to May, Costa Rica is truly a year round travel destination. In fact, there are often great deals to be had if you decide to visit Costa Rica during the off season. This is the greenest time of year, and though you will likely experience a few showers during your visit, it is a beautiful sight to see.
Other than the rainy and dry season, there are really no other significant variations in climate. The inland temperatures, such as those in the country's capital, are always moderate and generally come with a nice breeze. The coastal regions of Costa Rica do tend to be hot and humid in the June, July, August, and September months, but the cool ocean is an instant refresher. The greatest part of Costa Rica is that the annual average temperatures tend to be in the high 70s to lower 80s (25°C-29°C) with some months reaching the upper 80s (30°C to 31°C) which is all around pretty perfect weather.