This is due to the Coriolis effect, which is a result of the Earth's rotation. As the Earth spins, locations at the equator are moving faster than locations closer to the poles. This difference in speed causes a deflection in moving objects, like air currents.
In the northern hemisphere, the Coriolis effect causes winds to deflect to the right. This is why trade winds in the northern hemisphere blow from the northeast, and westerlies blow from the southwest.
