Why do hurricanes start in Africa and end in north America?

They don't ctually orginate in the Sahara, but rather the region to its south. During the summer, there is convergence of moist air, which leads to the formation of clusters of thunderstorms called tropical disturbances. These disturbance move west, out over the Atlantic Ocean. Here, they are fed by the moisture that evaporates from the warm water. If conditions are right, these disturbances will organize and strengthen, eventually becoming hurricanes. Many, but not all Atlantic hurricanes originate in this manner.