La Ceiba is one of the wettest cities in Central America, with annual rainfall around 3,200mm. There is no dry season as such, but the rainiest months are October through January. The driest period, relatively speaking, runs from February to May.
May is actually the best month to visit if you want to catch the Feria Internacional de La Ceiba — the carnival week makes the rain irrelevant. For outdoor activities in Pico Bonito, the February to April window tends to offer the clearest skies and more settled conditions for hiking and rafting.