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What Is the Fujiwhara Effect? Why Do Two Typhoons Sometimes Dance Together?

Key SummaryAn explanation of the interaction mechanism between two typhoons.

What Is the Fujiwhara Effect?

When two typhoons (tropical cyclones) come within approximately 1,000–1,200 kilometers of each other, they begin to orbit and pull one another around a "center of mass" located on the line connecting the centers of their circulations. This is known as the Fujiwhara Effect, which Japanese meteorologist Sakuhei Fujiwhara discovered in 1921 through experiments using a water tank.

Three Possible Outcomes When Two Typhoons Dance Together

The Fujiwhara Effect is not simply a "tango for two." The outcome depends on the relative sizes and strengths of the two typhoons:

  • A wide disparity in strength → merger: The stronger typhoon draws the weaker typhoon's circulation into its own system. The weaker typhoon dissipates, while the stronger one may intensify as a result—much like the big fish swallowing the small fish.
  • Comparable strength → mutual rotation followed by separation: The two typhoons orbit counterclockwise around their center of mass for a period of time in the Northern Hemisphere before being carried away by their respective steering flows.
  • One typhoon is flung away → a sudden change in track: The weaker typhoon may be thrown onto a track that deviates completely from the forecast. This is the main reason track forecasts can become highly inaccurate when two typhoons are interacting.

Classic Cases

  • MARIA and HINNAMNOR in 2018: The two typhoons initially orbited one another, causing their forecast tracks to change three times in a single day.
  • NESAT and HAITANG in 2017: HAITANG was pulled toward NESAT, and the two typhoons made landfall one after another in the same area of Fujian, resulting in a "double typhoon strike."
  • SAOLA, HAIKUI, and KIROGI coexisting in 2023: SAOLA traced a rare looping path over the coastal waters of Guangdong. The Fujiwhara Effect, combined with weakening steering flows, was the primary cause.

Why Does the Fujiwhara Effect Give Forecasters Headaches?

  • The intensities and separation distance of the two typhoons change every six hours, making their mutual orbital angular velocity difficult to calculate accurately.
  • Numerical models have difficulty representing the circulation of weaker typhoons, so their "pulling force" is calculated inaccurately, amplifying differences in forecast tracks.
  • When three typhoons coexist, as in September 2023, their interactions become a "three-body problem," causing uncertainty to increase exponentially.

What Should You Watch For When Two Typhoons Are Active?\n

During periods with two typhoons, check for track forecast updates more frequently—ideally consult the latest forecast every six hours. Do not make decisions based on a track map from two days earlier. Also pay attention to the wording used by meteorological authorities: when forecasts state that there is "considerable uncertainty in the track," defensive preparations should be made for the most adverse scenario.