The Coriolis Effect
The rotation of the Earth causes an interesting phenomena on free moving objects on the Earth. Objects in the Northern Hemisphere are deflected to the right, while objects in the Southern Hemisphere are deflected to the left.
The coriolis effect thus tries to force winds to shift towards the right or left. The coriolis effect can at times cause winds to blow back up the pressure gradient.
The coriolis effect and pressure gradient work against each other. Pressure gradient pushes winds outward, while the coriolis effect moves winds to the right or left. Often these two forces reach a balance, causing winds to blow sideways along the pressure gradient, not getting any further out from a high pressure or closer to a high pressure. This type of wind is known as a geostrophic wind.