Weather Blog

Can hurricanes cross the equator?

Can hurricanes cross the equator?
Hurricanes spin counter-clockwise in the Northern Hemisphere, and clockwise in the Southern Hemisphere due to the Earth's rotation and Coriolis Force.

Low pressure is due to areas of rising air, which then start to spin counter-clockwise due to the Coriolis Force. High pressure is tied to sinking air, which the Coriolis Force turns the air clockwise.

But let's say there's a hurricane off the coast of Mexico, and then it roars south toward South America where they would spin the other way. This is sort of like the axiom of what happens if you strap a piece of buttered toast to a cat's back, which way would point down? (And please don't test this at home.) As for hurricanes, what would happen?  Would it start spinning the other way?

The answer is no, because a hurricane would never cross the equator.  The Coriolis Force is near zero near the equator, so you don't get the turning needed to spin the air into tight low-pressure centers, so they don't form within 5 or so degrees latitude of the equator.

And for a theoretical situation for, say, aa roaring already-formed hurricane to charge forward at 20 mph and then drift south across the line, it can in theory -- the weak Coriolis Force there would just let it keep its momentum, and if it crossed, the opposite force would eventually tear it apart.

But the reason that's never happened a secondary part of the Coriolis Force tends to pull systems away from the equator, and in the area around the equator there are almost no upper level winds to steer a hurricane, so there would be no system to keep a hurricane alive before the other forces tore it apart.

So if you want to live in the tropics, but never want to have a hurricane, find some place right along the equator :)