The best wildlife viewing months in Tanzania are generally during the Dry season from late June to October. The best chance of seeing the wildebeest migration in the Serengeti however is during June and July and the time to see the wildebeest calving is late January to February.
January and February - hottest time of the year.
March - good time to go just before the big wet season and lots of wildebeest calves about!
April and May - wet season, flash rains.
June and October - pleasant temperatures.
November and December - secondary wet season, short rains.