Late spring (April–June) and early autumn (September–October) are the best months: hot but not punishing, sea warm enough to swim, and the worst of the package-tourist crowds confined to July and August.
Mid-summer can hit 35°C and the beach hotels fill up with European families, though the medina itself stays relatively quiet — locals retreat to the air-conditioned interior. Winter (November–March) is mild, around 15–18°C by day, and almost everything except the beach stays open. The fishing festival in late July or early August, the Festival du Cap Afrique, is worth timing a visit around.