Since Costa Rica has several micro-climates, it’s a good idea to understand when is the best time to visit Costa Rica for you.
The Pacific side experiences both a dry season and a wet season. The central valley area, where San Jose is located, is much milder with an average temperature of 72°F. The Caribbean side is much more humid all year round because of the trade winds. For this reason, this area receives more rain than other areas.
Since it’s a tropical country, Costa Rica’s “dry” and “rainy” (also called Green) seasons are really more like rough indications. You might experience some light rain even during the dry season, as opposed to heavier rains that you will experience during the rainy season.
For most parts of the country, and especially on the Pacific Beachside (which is the more desirable beachside), the dry season is usually December through April. So the best time to visit Costa Rica is usually within this window. Between mid-December through mid-January, and during the Easter/Holy week, hotels can be pretty expensive, so if at all possible I usually suggest people avoid these dates.
Costa Rica, (Guanacaste)
Personally, I find mid-February through March to be a good time to visit. If you are budget conscious, early-to-mid May is also a good time to visit. The rainy season would be just starting and not in full swing, so you will get to enjoy the lower green season rates and can expect a pretty good amount of sun.
July & August are a popular time to visit Costa Rica because of the summer vacations; however for that very reason, the prices during this “high season” are relatively higher than the rest of the rainy season. The months that I would suggest avoiding are June and September to early-October because the rain can be pretty heavy in most areas of the country. However, if you plan to have your beach stay on the Atlantic side of Costa Rica, September-October is actually better since it’s the dry season on that side of the country.