The long and heavy rain season starts in April, which is also the month of the heaviest rain, but it does not rain steadily all day long, most of the time it is characterised by short showers and thunderstorms; the sky is leaden with threatening clouds and the savannah grasslands turn bright green.
Rainfalls, however, are not enough to revive the Southern pastures that have been over exploited in the previous months, when the migrating animals stopped here during the birth delivery and the nursing of puppies.
An increasing number of animals point to the West and the centre of the park; they initially move somewhat disorderly, as they follow the storms, but soon the marching animals line up and form columns as long as 40-50 kms. 
The pastures here are less nutritious because the soil is not as rich in mineral salts as in Southern Serengeti and the Ngorongoro Conservation Area, but they remain green for longer due to the presence of water sources.
The herds linger in this area even after the heavy rain season, i.e. end of May, because thanks to the two lakes that collect rainfalls, both wildebeests and zebras find the water they need for a longer period than in other areas; but soon, when the grasslands begin to dry up and be over exploited, the herds restart their journey. 

Where is possible to spot the herds of Great Migration during the long rain season 

Moru Kopjes: this area, which links Ndutu to Seronera in Western Central Serengeti, is the privileged one by lions that use these great rocky formations as lookouts, in search of their prey.
Here also live giraffes, elephants, various species of antelope and buffalos; it is also home to some rhinos, but you need a bit of luck, as it is the only area in the park where you can spot them.
Seronera: the Seronera valley is located in central Serengeti and provides a rich source of food and water all year round; here live many animal species, including elephants, buffalos, antelopes and gazelles, but is also the favourite area for big cats, such as lions, cheetahs and leopards.
Leopards usually climb onto the trees flanking the river banks to view the surrounding land and any prey, and take refuge with their prey.
Lake Ndutu, Lake Masek and Lake Lagarja: the herds often linger in this area because of the water of these salty lakes that contributes to maintain the surrounding area green for longer, especially when the rain season comes to an end; wildebeests and zebra are the ones who set off sooner on their journey to the North.  Here  live ostriches, giraffes, various species of gazelle, impalas, jackals, spotted hyenas, striped hyenas, lions, crocodiles, hippos and, especially at this time of the year, many species of birds, some of which migrating from Europe. 

The alternation of seasons in Serengeti National Park and its effects on the Great Migration

  • Short dry season from January to March
  • Heavy rain season from April to May
  • Long dry season from June to October
  • Short rain season from November to mid-December