As Hurricane Dorian, one of the strongest storms ever recorded in the Atlantic, continues to batter the Bahamas and approach the United States mainland, millions of people who may be in its path are watching — and worrying. We asked readers what they want to know about Dorian. Answering those questions is Prof. Adam Sobel, an atmospheric scientist and director of the Initiative on Extreme Weather and Climate at Columbia University and the author of “Storm Surge,” a book about Superstorm Sandy.

[For the latest updates on Friday, read our Hurricane Dorian live briefing here.]

What makes a hurricane change course?

The motion of hurricanes is determined mainly by what meteorologists call the “steering flow,” or “environmental flow,” meaning the winds on a larger scale, excluding the swirling circulation of the hurricane itself. Think of the storm as a swirl you make in a river with a canoe paddle: It has its own little circulation, but the whole thing drifts with the river current on the larger scale. The environmental flow can vary in both speed and direction at different altitudes; the storm follows the low-level winds most, but the winds higher up also have an influence.

If left to itself, a hurricane would drift slowly toward the North or South Pole, depending on which hemisphere it is in. But the steering flows rarely leave a hurricane to itself. A hurricane turns when it encounters a steering flow that blows in a different direction than the storm was being driven before.