The Tanzanian climate is tropical on the coast, on the islands and in Selous. It is temperate inland and in the other parks. Tanzania has two distinct annual rainfall patterns, which prevail in different areas of the country: In the south, west, south-west and central regions, there is one rainy season, which occurs between December and April. In the northern and eastern regions of the country, there are two rainy seasons. The 'short rains' or Vuli last from October to December, and the 'long rains' or Masika last from March to May.

The warm Tanzanian summer lasts from mid-December till March, roughly corresponding with the rainy period of the south, west, and central region of the country. Winter, from June to October, is dry and cold across the country.

Tanzania's mountains are notable exceptions to its complex but otherwise regular climate. Temperatures on Mount Kilimanjaro and Mount Meru drop below freezing.
Between June and August it can be very cold at the Ngorongoro Crater while the coast is lovely at this time of year. The best time to visit Selous and Mikumi is from June to October, when the weather is cool & dry and the vegetation lush. The best months for game viewing in Ruaha are July to October (Yellow Season), when the animals are concentrated around shrinking water holes and the Ruaha River. For bird-watching, lush vegetation and wildflowers the best time is January and February (dry & warm). In March (wet season) tracks can become a bit difficult to traverse.