Mombasa, Kenya is located in a tropical zone close to the equator, causing its weather to vary very little over the course of the year.  The average temperature in Mombasa all year long is around 86 degrees F, with the average number of daylight hours also staying the same at around 8 hours per day.  Mombasa's average amount of precipitation does vary throughout the year however, with April and May topping out as the city's rainiest months.

Visitors enjoy coming to Mombasa all year long to enjoy its beautiful natural surroundings and tropical beaches, though some would choose to avoid coming in the late spring so as not to be caught in the rainy season.  In practice, even in the rainy season it does not usually rain all day or even every day. The showers tend to be relatively short but torrential, often in the late afternoon or overnight, and they can be very localised, it can be raining on one beach and fine on another a few miles away.

A bit more detail.

From November / December to early March, the Kenyan weather, particularly at the Coast, is dominated by the North East Monsoon (Kazkazi) which is comparatively dry. During March and April the monsoon winds start to blow in an east to south-easterly direction (Kuzi) which bring in streams of maritime air from the Indian Ocean bringing heavy rains. During the months of May, June, July and August, the South East Monsoon influence gradually sets in and the weather becomes more stable with a bit more cloud and comparatively cooler temperatures. Between September and November, the North East Monsoon gradually re-establishes itself and by December the northern influence is dominant once again.

Inland areas in East Africa experience two rainy seasons which occur shortly after equinoxes and two dry seasons occurring around the solstices. Due to the shape of the African continent and wind direction the greatest amount of rainfall occurs during the South East Monsoon, when the winds come in directly from the Indian Ocean . During the North East monsoon the air mass passes over the drier Somali land mass first and therefore coastal areas receive only a small rainfall peak. Inland areas receive more rainfall due to the expansion of a wet low pressure area from Central Africa which rarely reaches the coast.

 

For an up to date weather report on Mombasa, check the BBC's  Mombasa weather page.   

For local forecasts from the Kenya Meteorological Department see here http://www.meteo.go.ke/

For GFS Rainfall Forecast maps for the next 7 days see  http://www.wxmaps.org/pix/af.vv.html

To find out what the weather has been like in the past for the period of your trip, type 'Mombasa' and the dates fo your trip into the Trip Planner on this site http://www.wunderground.com/history/a...

And for the temperatures, rainfall, etc averaged over the last 21 years see here 

http://www.weatherbase.com/weather/we...

 

Also keep an eye on the tides. The tide  varies lots of meters and could enclose you if you take long beachwalks.

TIDES KENYA COAST