Twin Hurricanes the Fujiwara Effect Explained

What is more frightening and impressive than a hurricane or typhoon, pin-wheeling across the sea toward landfall? How about two or more cyclonic storms, spinning together under the influence of the Fujiwara Effect!

When any two rotating systems come into contact with one another, they will begin to orbit around their geometric center, and may eventually collapse into a single, larger system. This is known as the Fujiwara Effect, named for the Japanese meteorologist who first described the phenomenon, Sakuhei Fujiwara (1884-1950).

During particularly active seasons, any of the cyclonic storms (a hurricane, a typhoon, or a cyclone) may happen to meet another storm. When the two storms get within about 900 miles one another, they are drawn to one another and begin to orbit around a focal point between the two systems. If one storm is larger than the other, it will pull the smaller system into an orbit around itself. Equal-sized storms will swirl in an even interaction, spinning around a point half-way in between the eyes of the two storms. In either case, the storms will spiral ever closer together, and will eventually either merge or be flung apart by their rotational momentum. The outcome depends upon the speed with which they are moving, and the angle of their approach to one another.

Some examples of storms that experienced the Fujiwara Effect include 2005’s Hurricane Wilma, which absorbed Tropical Storm Alpha. In 1994, Pacific Typhoons Pat and Ruth made a complete orbit around their focus before merging into a single storm. Super-typhoons Ivan and Joan also interacted, but did not collapse together. Instead, both storms were sling-shotted off on new trajectories by the Fujiwara interaction, with Ivan heading to the west while Joan went north.

At times, more than two storms may come into contact, leading to increasingly complex interactions. The record-shattering 2006 typhoon season in the western Pacific saw a dance develop between what would become Super-typhoon Saomai, Tropical Storm Bopha, and Typhoon Maria. Saomai would go on to become the strongest storm ever to strike mainland China, causing 458 fatalities and around $2.5 US in damage. Bopha made landfall on Taiwan, but did not cause much damage. Maria headed for Japan, briefly gaining typhoon status before skipping off the eastern-most tip of Honshu Island, and failing to inflict any real harm.

One cyclonic storm can be awe-inspiring enough, but when two or more of them begin to dance around one another out at sea, anything can happen! The Fujiwara Effect is beautiful to watch on time-lapse satellite footage, but can also be deadly for people who live in the new path of the effected storms.