What is the Fujiwhara effect?

The Fujiwhara effect is a meteorological phenomenon where two nearby cyclonic vortices interact by orbiting around each other and closing the distance between their low-pressure areas. Depending on their size and proximity, this binary interaction can lead to the formation of a larger cyclone or cause the two systems to merge entirely. Named after the Japanese meteorologist Sakuhei Fujiwhara, the concept describes how extratropical and tropical cyclones behave when they come close enough to influence each other's circulation.

What we know

• The Fujiwhara effect is a meteorological phenomenon involving two cyclones interacting with each other, also known as the Fujiwhara interaction or binary interaction. [1, 2]
• Binary interaction of smaller circulations can result in the development of a larger cyclone or cause two separate cyclones to merge into one. [2]
• Extratropical cyclones typically engage in binary interaction when within 2,000 kilometres of each other, while tropical cyclones typically interact within 1,400 kilometres. [2]
• The effect is named after Sakuhei Fujiwhara, who initially described it in a 1921 paper based on an 1889 paper by a Japanese researcher. [2]

Where to go next

• whoWho was Sakuhei Fujiwhara?
• how it workedHow do tropical cyclones form?
• the bigger pictureWhat is an extratropical cyclone?
• whenHow did the 1921 paper shape modern meteorology?
• compared withHow do tropical and extratropical cyclone interactions differ?
• an unexpected connectionHow does a foundational 1889 study connect to modern weather forecasting?The Fujiwhara effect was originally built upon an 1889 research paper by a Japanese researcher before being formally described in 1921 and eventually adopted globally in the United States after World War II.

Sources

• [1]Fujiwhara effect (Wikidata Q1376614) · CC0 1.0
• [2]Fujiwhara effect · CC BY-SA 4.0
• [3]Tropical cyclones in 2026 · CC BY-SA 4.0
• [4]Tropical cyclone · CC BY-SA 4.0
• [5]Tropical cyclones in 2025 · CC BY-SA 4.0