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What is the Fujiwhara effect? Here’s what we know about the rare phenomenon.

What is the Fujiwhara effect?

The Fujiwhara effect happens when two tropical systems come near, then orbit each other, or possibly merge into one system.

What does ‘Fujiwhara effect’ mean?

The term “Fujiwhara effect” refers to the interaction between the two tropical weather systems. It is named for Sakuhei Fujiwhara, a Japanese meteorologist who first described the effect in 1921.

How does it start?

A couple of things have to happen for the Fujiwhara effect to take place. First, there have to be two storms involved. Second, they have to be within 870 miles of each other.

What happens then?

According to the National Weather Service, one of three things happen when the storms come near each other.

“When two hurricanes spinning in the same direction pass close enough to each other, they begin an intense dance around their common center,” the NWS website explains.

“If one hurricane is a lot stronger than the other, the smaller one will orbit it and eventually come crashing into its vortex to be absorbed.”

Or, if the two storms are close to the same size, they can gravitate toward each other until they reach a common point where they either merge or they spin each other around for a while before they spin off in different directions.

The third possibility is that the two systems come together to form a large storm instead of two smaller ones.