Dear Tom,
Do hurricanes and tornadoes always rotate in the same direction?
Melissa Quane,
Collierville, Tenn.

Dear Melissa,
Storms in the Northern Hemisphere always rotate in an anti-clockwise direction. Tornadoes usually rotate in a counter-clockwise direction – usually, but not always. Storms are low pressure systems. When viewed from above, the wind circulation around such systems (in the Northern Hemisphere) is always anti-clockwise. This is due to the deflection of the Coriolis effect, which acts to the right of the intended motion in air moving inward. In relatively small air circulations, such as in tornadoes, the force to deflect Coriolis is much weaker. As a result, the deflection to the right is weaker, and in about five percent of tornadoes the circulation is clockwise.


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