Nairobi has four seasons, but overall temperature changes are moderate. Mid‑ December through March are mainly sunny and warm by day, cool at night, and generally dry. April and May constitute the principal rainy season with lower day temperatures. The months of June through September are mainly dry, but often cloudy and cool, with cool nights. October and November make up the short rainy season, with long sunny periods, warm days, and cool nights. Average annual rainfall in Nairobi is about 39 inches, but the actual amount varies widely in any year.