January to February offers warm and mostly dry weather, ideal for visiting Zanzibar's beaches or climbing Mount Kilimanjaro. It's mostly dry, with just brief afternoon showers.
March to May is the low season due to the heavy “long rains”, especially in the coastal and northern safari regions. However, if you don't mind the rain and muddy roads, you'll enjoy lush landscapes, fewer tourists and discounted accommodation. Zanzibar, however, is best avoided during this period.
June to September is the main dry season, not as humid, and is considered the high season for holidays to Tanzania. It's the best time for safaris, as animals gather around water sources, making them easier to spot.
October to December sees the second and lighter “short rains”, which are a little unpredictable but generally fall for a month during this time. It's a quieter time to visit with fewer crowds, and despite occasional downpours, it's a good time for bird-watching, especially around Lake Manyara. In the south, the rains sometimes arrive early, tagged onto the end of the long rains, increasing the length of the dry season.