Here's what happens when two hurricanes collide

What happens when two hurricanes collide?

The phenomenon is called the Fujiwhara effect.

Named for Japanese meteorologist Sakuhei Fujiwhara, who originally described it in 1921.

If two cyclones pass within 900 miles of each other, they can start to orbit.

What happens next depends on the size of each storm.

If one storm is much stronger than the other, the smaller storm usually rotates around the larger one.

But when bot storms are similar in strength, they tend to orbit a common center between the two.

If the two storms get to within 190 miles of each other, they'll collide or merge.

The result is transformative.

It can turn two smaller storms into one giant one.

The interaction can also throw a cyclone off course.

That's what happened in July 2017 with hurricanes Hilary and Irwin.

Hurricane Hilary changed Irwin's course from west to north.

This example is more the exception than the norm.

Hurricane collisions and interactions are rare.

Yet, growing evidence suggests a warming climate could affect hurricane season.

What the effects will be is unclear, but who knows?

Perhaps more hurricane mergers are in our future.