The rainy season occurs from May until November, although the rain seems to slacken in July, when the average rainfall is about 8.3 inches.
The best time to visit the beach is during the dry season, which typically is from December to May, when temperatures are usually between 75 and 80 degrees Fahrenheit and average precipitation is less than two inches.
Fishing in Costa Rica is excellent for much of the year. It's particularly good bill fishing in Quepos from December until April. The marlin migrate north, so Guanacaste is a popular spot for bill fishing during the rest of the year. October is usually too rainy for fishing, with an average rainfall of about 12 inches.
If you plan to visit the volcanoes during your trip, be sure to avoid traveling between June and October, which are some of the rainiest months, averaging between 9.5 to 12 inches of rain.
Costa Rica's busy travel season tends to be in the wintertime as a respite from cold weather elsewhere. In addition, Costa Rica is a Roman Catholic country, and beaches tend to be more crowded than usual around Christmas and Easter.