While February is normally a dry month, the rains being experienced now in Kenya and other countries are due to the shifting of the Congo moisture band (a meridional arm of ITCZ) into Eastern Africa Countries.
The Kenya Meteorological Department explains that the shift is currently caused by the existence of a depression within the Mozambican channel -the area between Madagascar and Mozambique-. This creates a pressure gradient causing the airmass to temporarily move eastward.
The ITCZ (Intertropical Convergence Zone) is a band of low pressure and associated moisture. Its movement north and south follows the movement of the sun north and south while its movement east and west is influenced by pressure gradients.
The current rains are expected to continue into early next week.