São Luís has a tropical climate with a distinct wet and dry season. The rainy season runs roughly from January to June, with the heaviest rainfall in March and April. The dry season runs from July to December and is the most comfortable time to visit — lower humidity, clear skies, and consistently warm temperatures.
The city's most famous festival is the Bumba Meu Boi, a spectacular folk pageant celebrated in June. Elaborate costumes, complex music mixing indigenous, African, and European traditions, and performances that can last through the night: it is one of the most culturally distinctive festivals in Brazil and worth timing a visit around.
The months of July and August are ideal: the festival season has just ended, the weather is dry and pleasant, and the beaches are at their best. The period around Carnival (February/March) is lively but the rain is usually heavy.