Cape Verde has two seasons: dry and less dry. The dry season runs from November to June, and this is when most travelers visit. The wet season, from July to October, brings occasional rain -- mostly concentrated in August and September -- and higher humidity, but temperatures stay warm year-round. Expect daytime highs between 24 and 30 degrees Celsius regardless of the season.
November to March is the peak season and the best all-round time to visit. The trade winds blow steadily, making it ideal for kitesurfing and windsurfing on Sal and Boa Vista. Hiking on Santo Antao is excellent in dry, clear conditions. This is also when European charter flights are most frequent, so accommodation on the beach islands books up and prices rise. Be aware of the Harmattan, a dusty wind from the Sahara, which can ground flights and reduce visibility between December and March.
April to June is a sweet spot -- fewer tourists, lower prices, warm seas, and calm winds. The water temperature is at its best for swimming and snorkeling. Hiking is still good, though the vegetation on the mountainous islands starts to dry out.
July to October is the wet season, and the least popular time to visit. Rain is sporadic and rarely lasts long, but it can disrupt travel on mountainous islands where roads wash out. The upside: the green islands -- Santo Antao, Santiago, Fogo -- come alive with vegetation, and you may see waterfalls that do not exist the rest of the year. This is also turtle nesting season on Boa Vista, where loggerhead turtles come ashore at night between July and October to lay eggs.
Carnival in Mindelo falls in February and is Cape Verde's biggest cultural event. If you time your trip around it, book accommodation on Sao Vicente well in advance -- the island fills up fast.