The Fujiwhara Effect

The Fujiwara Effect is an interesting phenomenon that can happen when two or more hurricanes form 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.

Fujiwara's studies indicate storms will rotate around a common center of mass. A similar effect is seen in the rotation of the Earth and the 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 tropical storms. This interaction will sometimes lead to tropical storms 'dancing' with each other around the dance floor of the ocean.

Examples of the Fujiwhara Effect

In 1955, two hurricanes formed very near each other. Hurricanes Connie and Diane at one point seemed to be one huge hurricane. The vortices were moving around each other in a counterclockwise motion.

In September 1967, Tropical storms Ruth and Thelma began to interact with each other as they approached Typhoon Opal. At the time, satellite imagery was in its infancy as TIROS, the world's first weather satellite, was only launched in 1960. To date, this was the best imagery of the Fujiwhara Effect yet seen.

In July of 1976, hurricanes Emmy and Frances also showed the typical dance of the storms as they interacted with each other.

Another interesting event occurred in 1995 when four tropical waves formed in the Atlantic. The storms would later be named Humberto, Iris, Karen, and Luis. A satellite image of the 4 tropical storms shows each of the cyclones from left to right. Tropical storm Iris was heavily influenced by the formation of Humberto before it, and Karen after it. Tropical Storm Iris moved through the islands of the northeastern Caribbean during late August and produced locally heavy rains and associated flooding according to the NOAA National Data Center. Iris later absorbed Karen on September 3, 1995, but not before altering the paths of both Karen and Iris.

Hurricane Lisa was a storm that formed on September 16, 2004, as a tropical depression. The depression was located between Hurricane Karl to the west and another tropical wave to the southeast. Like a hurricane, Karl influenced Lisa, the quickly approaching tropical disturbance to the east moved in on Lisa and the two began to show a Fujiwhara Effect.

Cyclones Fame and Gula are shown in an image from January 29, 2008. The two storms formed just days apart. The storms briefly interacted, although they remained separate storms. Initially, it was thought the two would exhibit more of a Fujiwhara interaction, but despite weakening a bit, the storms stayed intact without causing the weaker of the two storms to dissipate.

Sources

• Stormchasers: The Hurricane Hunters and Their Fateful Flight Into Hurricane Janet
  NOAA National Data Center
  
• Annual Summary of the 2004 Atlantic Hurricane Season
  
• Annual Summary of the 1995 Atlantic Hurricane Season
  
• Monthly Weather Review: An Example of the Fujiwhara Effect in the West Pacific Ocean
• NASA Earth Observatory: Cyclone Gula
• Cyclones Olaf and Nancy