Palermo has a Mediterranean climate with hot, dry summers and mild, wet winters. May and June are ideal, with warm temperatures perfect for walking and beach days. July and August are hot and can be oppressive in the city centre, though evenings are pleasant. The Santa Rosalia festival in mid-July brings parades and fireworks.
November is the wettest month, but rainfall is still modest. Winter is mild, rarely dropping below 10C, and you will have the sights largely to yourself.