Cuba has a tropical climate, so the country is generally hot and humid all year round with an average of 25°C, and the very best time to visit Cuba is from November to April, during the dry season.
However, temperatures can drop to be quite cool (15°C) in the winter months of January and February, so be sure to bring along some warmer clothing.
The rest of the time is rainy season, though usually showers are over as soon as they begin and the sun and warm temperatures dry everything out quickly. June to November is the official hurricane season.