Although Nairobi is situated in the middle of East Africa, its high altitude—about a mile above sea level—means that the city's climate is mild year-round. Visitors are spared the extreme, blistering temperatures found in other regions of Africa, or even other areas within Kenya. Summer months in Nairobi are December through March, when average highs are in the upper 70s and lows are in the mid- to upper-50s. Winter months (June through September) are a little cooler. Average highs are in the lower 70s, and lows are in the lower 50s.

There are two distinct rainy seasons that occur in Nairobi, one in the spring months of March to May, which is locally referred to as the 'long rainy' season.  April is the wettest month during this period brining upwards of eight inches of rain on average.  The other rainy period occurs between mid-October to mid-December, the period referred to locally as the 'short' rainy season.  November sees approximately five inches of rain.  During the rest of the year, around two inches a month can be expected. 

February sees the most sunshine in Nairobi, with about ten hours of daylight. Half a year later, in August, sunshine lasts for about five or six hours.

Here is the link to: Nairobi Kenya Weather - Five Day Forecast