Recife is tropical and warm year round, with daytime highs in the high 20s to low 30s celsius. The rainy season runs roughly April to July: short, heavy showers most afternoons, often followed by sunshine. The dry season runs September to February and is the most reliable for beach time.
The peak event is Carnival, in February or early March. Recife and neighbouring Olinda put on one of the largest street carnivals in Brazil, with the famous Galo da Madrugada parade — sometimes credited as the largest single carnival bloco in the world — drawing more than a million people through Recife Antigo. Accommodation books out months in advance and prices double; if you are not coming for the parties, avoid carnival week.
The second peak is mid-year, in late June, for the São João festivals — quieter than carnival but culturally as important in the northeast.