Weather Explainers

Weather Words: Coriolis Effect

The Coriolis effect is the apparent bending of winds and currents caused by Earth’s rotation, shaping the swirl of storms and global weather patterns.

Have you ever wondered why big storms spin like pinwheels instead of sliding straight across the Earth? Or why air and ocean currents don’t just travel in straight lines across the planet? Well, that’s the Coriolis effect.

The Coriolis effect is the apparent bending of moving objects, like air and water, as they travel across the rotating Earth. Because our planet spins, anything moving long distances doesn’t travel in a straight line relative to the surface. Instead, motion appears to curve to the right in the Northern Hemisphere, and to the left in the Southern Hemisphere.

Just as the Coriolis effect deflects winds to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, it also results in the deflection of major surface ocean currents to the right in the Northern Hemisphere (in a clockwise spiral) and to the left in the Southern Hemisphere (in a counter-clockwise spiral).
(NOAA)

This effect plays a major role in global weather patterns. It helps determine the direction of winds, shapes large-scale circulation like trade winds and jet streams, and is a key reason storms rotate.

In the Northern Hemisphere, low-pressure systems spin counterclockwise. While in the Southern Hemisphere, they rotate clockwise. The Coriolis effect is weakest at the equator and strongest near the poles, which is why hurricanes can’t form right at the equator and why weather systems behave differently depending on latitude.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.