Why do storms on the mainland head from west to east but storms like hurricanes move east to west?

Dear Tom,
Why do storms on the mainland head from west to east but storms like hurricanes move east to west?
— Kirk Light Jr., Hanover Park
Dear Kirk,
The movement of weather systems over the United States and hurricanes over the Atlantic Ocean (and elsewhere) is determined primarily by distance from the equator. The Earth is divided into east-west-oriented weather zones. The region of the Earth that extends about 23 degrees north and south of the equator is the tropics. The region northward (and southward) from there to about 35 degrees north (and south) is the subtropics. Northward from there to about 65 degrees north (and southward to 65 degrees south) is the midlatitudes. Wind circulation and the movement of weather systems are generally east to west in the tropics and subtropics, and west to east in the midlatitudes.

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