Tanzania has a mostly tropical climate with hot, humid weather with lots of rain. It is generally warmer and drier inland and cooler and more humid on the coast. The average annual temperature is 73°F. The best weather for the beach is just after the main rainy season in July, while the best time to safari is just after Christmas (January to February), when herds gather en masse in the Serengeti plains.
March through May should be avoided. While temperatures are not extreme, torrential rains cause many routes to become impassable. Though the animals are migrating north, this is not the time to safari or visit the beaches, even though hotel rates are cheaper to entice visitors. There is a shorter rainy period November through January, which proceeds the cool season and is the time when animals are grazing and there are lots of lions around.
Zanzibar and the beaches can be nice most of the year, but the time to avoid is April and May. You may need a jacket for cool nights if in the interior between June and September, while Mount Kilimanjaro has temperatures below zero due to the altitude. The rim of the Ngorongoro Crater also gets chilly.
Best Time to Visit Tanzania
Weather-wise, June through August is the best time to visit Tanzania as this is the dry season, with lower temperatures, less humidity and little rainfall. This is the best period to see the cities and the beaches, although it is not the best for safaris. While the animals are always there, the ponds, lakes, and rivers are still topped up, along with plenty of grazing from the preceding rains so the animals remain spread out.
For safaris, the best time to see wildlife is late December/early January through February, when the animals head north for better vegetation and water. It is hotter, but not as bad as September/October when wildebeest can be seen crossing the Mara River during their annual migration.