text: Tropical cyclones can form on both sides of a basin, but there are indeed generally fewer of them the farther east one goes.  As a general rule, the western halves of ocean basins have a larger expanse of warm water that TCs need compared to the eastern sides, which often have large expanses of cool water.  Also, the eastern halves of ocean basins also tend to be regions of dry, descending air, while the western halves have rainier, more tropical conditions.