Fujiwara Effect

The Fujiwhara effect or Fujiwara interaction, named after Sakuhei Fujiwhara, is a type of interaction between two nearby cyclonic vortices, causing them to appear to "orbit" each other.

When the cyclones approach each other, their centers will begin orbiting cyclonically about a point between the two systems due to their cyclonic wind circulations. The two vortices will be attracted to each other, and eventually spiral into the center point and merge. When the two vortices are of unequal size, the larger vortex will tend to dominate the interaction, and the smaller vortex will orbit around it.

The effect is often mentioned in relation to the motion of tropical cyclones, although the final merging of the two storms is uncommon. The effect becomes pronounced in these storms when they approach within about 1,500 km (900 mi) of each other and are at tropical storm strength or stronger.

The effect is named after Sakuhei Fujiwhara, the Japanese meteorologist who initially described it in a 1921 paper about the motion of vortices in water

The Fujiwara Effect is an interesting phenomenon which can happen when two or more hurricanes form very near each other. In 1921, a Japanese meteorologist named Dr. Sakuhei Fujiwhara determined that two storms will sometimes move around a common center pivot point.

The National Weather Service defines the Fujiwhara Effect as the tendency of two nearby tropical cyclones to rotate cyclonically about each other. Another slightly more technical definition of the Fujiwhara Effect from the National Weather Service is a binary interaction where tropical cyclones within a certain distance (300-750 nautical miles depending on the sizes of the cyclones) of each other begin to rotate about a common midpoint. The effect is also known as the Fujiwara Effect without an ‘h’ in the name. USAToday provides an excellent graphic explaining theFujiwhara Effect.

Fujiwhara’s studies indicate storms will rotate around a common center of mass. A similar effect is seen in the rotation of the Earth and moon. This barycenter is the center pivot point around which two rotating bodies in space will spin. The specific location of this center of gravity is determined by the relative intensity of the tropical storms. This interaction will sometimes lead to tropical storms 'dancing' with each other around the dance floor of the ocean.