Nairobi's high altitude — about 1,660m above sea level — keeps the climate mild year-round. Temperatures rarely exceed 28°C in the warmest months or drop below 10°C at night in the coldest. The sun is strong at this elevation; don't underestimate it.
Kenya has two rainy seasons: the long rains from March to May (April is often the wettest month), and the short rains from October to December. Both rainy seasons bring afternoon downpours rather than all-day grey skies — mornings are often clear and sunny even in the wettest months. The dry seasons (January–February and June–September) are the most reliable for wildlife viewing and outdoor activities.
The best time for a Nairobi National Park visit is June to September, when animals concentrate around shrinking water sources. The wildebeest migration in the Masai Mara — a common add-on for Nairobi visitors — peaks in July to October.
The Nairobi International Book Fair takes place in September. Madaraka Day (June 1) and Jamhuri Day (December 12) are the major national holidays; the city fills with parades and public celebrations. Horse racing at the Ngong Racecourse takes place most Sundays between April and July.