 The Coriolis force imparts rotation on the flow and arises as winds begin to flow in toward the lower pressure created by the pre-existing disturbance.In areas with a very small or non-existent Coriolis force (e.g.near the Equator), the only significant atmospheric forces in play are the "pressure gradient force" (the pressure difference that causes winds to blow from high to low pressure) and a smaller friction force; these two alone would not cause the large-scale rotation required for tropical cyclogenesis.