The best time to visit Tanzania depends on what you would like to see. There are two distinct rainy seasons: from the end of March to early June, and from the end of October to mid-December. Rain is normally in short, sharp downpours with clear skies between.
From January to March it is hot and dry. June to October is warm and dry, with colder evenings.
Game viewing is good throughout the year, although the migration leaves the Serengeti for the Masai Mara at the end of March / beginning of April, arriving in Kenya in late June / early July. The return migration leaves Kenya in October and arrives in the Serengeti in December, depending on the year’s rainfall.