The beginning of the rainy season is observed with a celebration which lasts for several days and includes singing, dancing, eating, and praying for the health of their animals. here are two dominant influences on the climate in Kenya: the onshore monsoon winds from the Indian Ocean, and altitude. The winds determine the onset of Kenya’s two rainy seasons, with the hot northeast monsoon or kaskazi blowing dry air in from the Persian Gulf from November to March/April and the warm, moist kusi monsoon blowing in from the southeast from April/May to October.

It’s the slightly cooler kusi that normally delivers the heaviest rain, a season known as the ‘long rains’, in late-April, May and early June. The relatively cool season, from late-June to October, gets much less rain. There’s a second rainy season, the ‘short rains’, for a few weeks in November and December, followed roughly from mid-December to March by a dry season of hot, usually rainless, weather.

Source: https://www.expertafrica.com/kenya/info/kenya-weather-and-climate