Olinda is hot and humid year-round — this is the Northeast Brazilian coast, and there is no cool season to speak of. The rainy season runs roughly from April through August, when Recife and Olinda receive the bulk of their annual rainfall. Heavy afternoon downpours are common during these months, though mornings are often clear. From September to March the skies are more reliably dry and sunny, and the sea is calmer for swimming at nearby beaches.
Carnival, held in February or March depending on the lunar calendar, is Olinda's defining event. The bonecos gigantes processions and the frevo dancing in the streets draw enormous crowds — far more intimate than Rio or Salvador, and with a distinctly local character. Accommodation fills months in advance and prices rise sharply. If you want to experience it, book early and stay in Olinda rather than Recife; the distance is short but the crowd movement is unpredictable.
Outside Carnival, the town is quieter and the narrow streets are easy to walk. Weekends bring day-trippers from Recife, so weekdays offer a more relaxed visit. The hilltop Sunday artisan market at the Alto da Sé is worth timing a weekend trip around.