The Atlantic Hurricane season officially begins Sunday, June 1, and runs through November 30. Last week various agencies released their predictions for how many hurricanes might develop and how many might be big ones. The U.S. National Oceanic and Atmospheric Administration, which overseas the National Weather Service, forecasts a below-average season, with three to six hurricanes, only one or two of which would reach Category 3 strength or higher. The Weather Channel, which is an independent, commercial outfit, predicts five hurricanes, with two reaching Category 3 or better.

These annual predictions can be off by a fair amount. They are usually in the right ballpark, but considering that the ballpark is less than 12, that’s not a stretch. One factor this year is that meteorologists are seeing mounting evidence that a strong El Nino pattern will develop in the equatorial region of the Pacific Ocean during the summer. That tends to increase wind shear across the central Atlantic, which can help pull apart nascent hurricanes there, although not always. So we’ll see what happens.

Much more precise is our understanding of how hurricanes form. We put together a video and animation to explain that, which you can view below.

Hurricanes that arise in the Atlantic usually form off the coast of Africa and cross the tropics. As soon as one of these disturbances arises, the National Hurricane Center starts to track it, in exquisite detail. You can follow along on the center’s cyclone page.