Map from Google - Serengeti

The climate of the Serengeti National Park is subtropical, with a dry and relatively cool season from May to August, a warm and still quite dry season in September and October, and a rainy and quite hot season from November to April.
The park is located at an altitude between 1,100 and 2,000 metres (3,600/6,600 feet); the altitude tempers the heat, so even though we are just south of the Equator, at night it can be cool, or even cold in the highest areas and in the cool season. But the sun is very strong, and requires appropriate protection, especially when it passes the zenith and is higher at noon (ie around mid-March and the end of September).
Here are the average temperatures of the Ikoma Safari Camp, at 1,400 metres (4,600 feet) of altitude.
Average temperatures - Serengeti
Min (°C)161616161615141515161616
Max (°C)292929282727262728292828
Min (°F)616161616159575959616161
Max (°F)848484828181798182848282

Rainfall hovers around 900/1,000 millimetres (35/40 inches) per year in much of the park; in the north it gets to 1,400 mm (55 in), while in the southeast, the most arid area, it drops below 800 mm (31.5 in). The rainy season is actually divided into two, with an interim period which is not actually very dry: from October to December we have the "short rains season", and from March to May (but in the southern part from February to April) the "long rains season". Consequently, the rains diminish, but in a not very pronounced way, in January and February, when still between 80 and 100 mm (3.1 and 4 in) of rain per month fall.
Here is the average precipitation.
Average precipitation - Serengeti
Prec. (mm)80100130155903515305570115105980

Elephant and antelopes in the Serengeti

The park is famous for the animals of the savannah, but especially for the so-called "Great Migration", involving about two million mammals, especially wildebeest and zebras, which move throughout the year between the Serengeti and the neighbouring Masai Mara, in Kenya, while their predators, such as hyenas and big cats, are more sedentary. The animals travel in a circular migration, staying in the Serengeti from November to June, while from July to October they move to the Mara, especially in August and September. The reason why in this period (which corresponds to the austral winter) the animals migrate to the north, is that the dry season in the Serengeti is more pronounced than in the Mara, which is located closer to the Equator and therefore remains wetter, and equipped with lusher pastures. The exact location where the herds are located at any given time depends on the rains, and therefore can not be predicted with certainty, however, we can give some general guidelines.
In January and February, the animals are scattered south of the Serengeti, in the area of the Olduvai Gorge, north of the crater of Ngorongoro, in a semi-arid zone where the grass is low, and it's easy to spot any predators such as hyenas and lions, of which there is no shortage.
Between February and March, the animals give birth to puppies, who become immediately able to move independently, and head west, in the area of Lake Ndutu.
In March, the season of the long rains begins, and the animals follow the lightnings that indicate thunderstorms, and move to the north, in search of green pastures, entering the Serengeti and heading towards the swamps west of Seronera, in the direction of Lake Victoria.
Between May and June they are in heat and mate, and then continue to the north, heading towards the Grumeti River, which they will have to cross, each time choosing a different point. In June and July they are marching towards the northeast, to the Masai Mara. From July to October they remain in the Masai Mara, where they move around in search of pasture available. From late October to December, in the short rains season, they return again in the Serengeti, moving southward.

The Serengeti National Park is bordered by other parks, like the aforementioned Mara in Kenya and Ngorongoro to the southeast, the Maswa Game Reserve to the southwest, and Grumeti and Ikorongo to the north-west.

The amount of sunshine in the Serengeti is good most of the year, since the rains come in the form of downpour or thunderstorm in the afternoon. However, in the period of the long rains, rainfall and cloud cover can last longer, even though the sun shows up for a few hours a day.

Serengeti, wildebeest crossing a river

When to go

From a climatic point of view, the best time to go to the Serengeti goes from June to September, being the dry season; it's better to be equipped for the cool or cold at night, especially at higher altitudes. In September the temperatures begin to increase, and it can get a bit hot at lower elevations. During the month of October, the short rains season begins.
In June, the herds of wildebeest are located in the northwestern part of the park, in the area of the rivers Grumeti and Mara (Mara Region), where you can watch them when crossing rivers, while in July they move to the Masai Mara.
At the end of October or in November, the wildebeest return to the Serengeti, when however the short rains season has begun. For watching them in the other seasons, you can therefore choose January and February, in the "short dry season", when they are in the southern part of the park or in nearby Ngorongoro, and they are in breeding season.