At the beginning of the year, January and February, the lack of rainfall tends to attract the crowds and although this is considered the best time to visit Costa Rica be aware that prices are higher and popular national parks such as Manuel Antonio can get busy.
As March and April are still relatively dry there are plenty of reasons to visit Costa Rica over Easter with the chance of afternoon and evening downpours increasing with warmer temperatures during May and June.
The warmer and wetter weather continues throughout July and August with more families attracted to Costa Rica during traditional northern hemisphere school vacations.
If you’re hoping to witness nesting green turtles, the best time to visit Costa Rica is July to Oct (peaking in Aug) and leatherbacks from Feb to April. Olive ridley turtles come to Ostional to lay their eggs between Aug and Dec. Humpback whales pass by Caribbean and Pacific coasts from Aug-Oct and Dec-April; dolphins can be seen all year round.
September and October are notoriously rainy in Costa Rica with many roads impassable due to swollen rivers and mud slides. Rural regions, such as the Osa Peninsula often close completely so take this into consideration if traveling independently.
Masses of migratory birds also head to Costa Rica from Oct to Nov with falcons, hawks, swifts, swallows, wrens and warblers joining endangered great green macaws which tend to return in Sep-Oct to make the most of blossoming almond trees.
There are still showers in November but come December temperatures start to fall and you’ll find an intensely green tint to the rainforests with animals appearing from thick foliage; there are also some good prices to be had at the tail-end of the rainy season before Christmas kicks in.