Some of the victims drowned and others suffered fatal electric shocks, according to Police Chief George Seda, who warns that the death toll could rise.
Heavy rain began on Friday and continued into Saturday.
Many vehicles were trapped in the water and motorists were forced to flee to higher ground. Homes were also flooded. Some air traffic has been diverted or canceled.
The military is assisting rescue services in finding missing and stranded people.
Kenya has been hit hard by torrential rains since the rainy season started at the end of February.
