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Dry season and green season
On the Pacific side and in the Central Valley, the dry season usually runs from about December to April and the green (rainy) season from about May to November. September and October are typically the wettest months on the Pacific. Green-season mornings are often clear, with rain in the afternoon.
| Region | Generally drier | Generally wetter | Notes |
|---|---|---|---|
| Guanacaste | Dec–Apr | Sep–Oct | Driest region overall |
| Central & Southern Pacific | Dec–Apr | Sep–Oct | South is wetter than Guanacaste |
| Caribbean | Often Sep–Oct and Feb–Mar | Varies; rain possible year-round | Pattern differs from the Pacific |
| Arenal & Monteverde | Feb–Apr | Varies | Cloud and mist common all year |
Wildlife seasons
- Humpback whales off the Southern Pacific: roughly July–October and December–March.
- Green turtle nesting at Tortuguero: roughly July–October (guided night tours only, rules set by the park).
- Birds are year-round; migrants add variety roughly October–April.
Tradeoffs
The dry season has the most sunshine and the highest demand, especially around Christmas, New Year and Easter. The green season brings fuller rivers and waterfalls, greener landscapes and usually more room on tours, but some roads and boat trips can be affected by weather.