Sitting on the equator, Kenya and Tanzania enjoy temperate climates and are pretty much year-round destinations; as you'll notice from the charts below, there is remarkably little fluctuation in monthly temperatures. However, temperatures on the rim of the Tanzania's Ngorongoro Crater drop dramatically at night, particularly June to August, so pack a warm layer or two. Temperatures drop below freezing on Mount Kilimanjaro (and Mount Meru at certain times), where there is permanent snow on the highest peaks. To keep an eye on local weather patterns, visit www.africanweather.net.
Seasonal fluctuations mostly relate to rainfall, which -- in game-viewing regions -- can have a dramatic impact on animal populations and accessibility, and consequently also on accommodations prices. Generally there are two seasons, dry and rainy. The best months for game viewing are generally the dry seasons, which are January to March and June to September. At these times, vegetation is light and there is no surface water created by the rains that disperse the animals, and instead they congregate around the remaining rivers and waterholes. Drier weather also means less hassle by mosquitoes. Many safari lodges and camps will close during the "long rains" in April and May -- considered low season -- and this is when you'll score the best deals on lodging and are least likely to feel besieged by other travelers. However, getting around at this time (as well as in Oct and Nov, during the so-called "short rains") can be difficult, as dirt roads turn to mud, and many become impassable.
Top season to visit Kenya's Masai Mara and Tanzania's Serengeti is during the Migration, which starts as early as July and can continue through November (though Aug-Oct are the most productive months); however, this period is generally marred by popularity, as visitor numbers soar and the best viewing areas are mobbed by homo sapiens. Note also that the Migration continues year-round, with most of the movement happening in Tanzania's Serengeti, so you can plan to incorporate the Migration pretty much any time of the year, as long as you're flexible about where to go. Toward the end of May, when the rains abate, the Migration moves north and/or into the western corridor, and the river crossings usually happen in July. Between August and October, the herds are at the Mara River (in the far northern Serengeti), and over these months they cross backward and forward, in and out of Kenya, drawn by localized rain showers. In November, when the rain clouds usually gather to green the south, they again cross the Mara, passing through the eastern Serengeti to return to the short-grass plains of the southern Serengeti in December.
Bird-watchers will want to visit in the winter months from October to April, when many birds migrate to East Africa from Europe.
Calving season usually occurs January to March in Tanzania's southern plains. This is an incredible time to be in the Serengeti, with thousands of calves being born every day, and -- thanks to the short-grass plains -- the riveting predator action in clear view.
Kenya and Tanzania's coasts and Zanzibar can be visited at any time of year, although again the rainy seasons may hamper beach time. They enjoy a tropical climate with average daytime temperatures of 30°C (86°F) and long hours of sunshine, making them a perfect destination for a beach vacation. During the day the humidity is tamed by sea breezes, but it can feel sultry at night. High season on the Kenyan and Tanzanian coasts is November to February, when it's a popular winter sun destination from the Northern Hemisphere.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.