MadSci Network: Earth Sciences

Re: Why do hurricanes move north, against the trade winds?

Date: Thu Apr 8 21:37:05 1999
Posted By: Carl Morgan, , Meteorology, National Weather Service
Area of science: Earth Sciences
ID: 921297539.Es


The force created by the earth's rotation is called the Coriolis Force. This force does not help steer hurricanes toward the equator, as you hinted at in your question.

Rather, when air is in motion in the Northern Hemisphere, the Coriolis Force deflects the air to the right. Therefore, as the trade winds blow the hurricane to the southwest, the Coriolis Force turns the storm right (to the north), where it is picked up by the Westerlies, as you mentioned.

The Coriolis Force is zero at the equator, and increases poleward. Because of this, hurricanes cannot form within 2 or 3 degrees latitude of the equator.

For more information, check out this link from the University of Illinois.

Admin note--Richard Kingsley adds the following:

The logical answer to the question is that the winds are not flowing Southward (which is what the posted answer suggests), but this would seem to contradict what you have taught them.

If one of your students asks you about hurricanes then this is what you can tell them.

The four major wind belts are a very simplified view of the global wind system and there is variation both geographically and temporally. In the summer when hurricanes are most prevalent, the Southward component of the trade winds are non-existent over the Carribean. The winds flow Westwards (at least according to a wind map I have).

This allows hurricanes to move North due to the coriolis effect and get picked up the the Westerlies.

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