When hurricanes collide!
The Fujiwhara Effect
The Fujiwhara effect describes the rotation of two storms around each other. It's most common with tropical cyclones such as typhoons or hurricanes, but also occurs in other cases. When Tropical Storm Iris was approaching the Windward Islands on Aug. 23, 1995 and Hurricane Humberto was close behind, they drew close enough together to begin a Fujiwhara dance. The effect is thought to occur when storms get about 900 miles apart. As Humberto chased down Iris, Humberto began to lift northward over Iris while Iris slowed down and turned a bit to the south. Iris became a hurricane just as this "dance" began but both storms were weakened by their passion for each other. As they weakened other forces in the atmosphere broke them apart and sent them on their separate ways. About 8 days later, Iris, now a hurricane with 110 mph winds, was moving northward east of Bermuda. This time Tropical Storm Karen scooted in behind Iris. But Karen was a much weaker storm with winds of only 45 mph. As the storms moved closer the Fujiwhara effect began. But Iris' strength dominated and poor Karen was flung around Iris to the north and Iris absorbed Karen right into its circulation while barely flinching. Storms involved in the Fujiwhara effect are rotating around one another as if they had locked arms and were square dancing. Rather than each storm spinning about the other, they are actually moving about a central point between them, as if both were tied to the same post and each swung around it separately of the other. A good way to picture this is to think of two ice skaters who skate quickly towards each other, nearly on a collision course, grab hands as they are about to pass and spin vigorously around in one big circle with their joined hands at the center. To complete the effect, the entire system - the two storms and the central point between them - must move off in a single direction while the storms continue spinning about each other. The effect is named after Dr. Sakuhei Fujiwhara who was the Chief of the Central Meteorological Bureau in Tokyo, Japan, shortly after the First World War. In 1921 he wrote a paper describing the motions of "vortices" in water. Water vortices are little water whirls that spin around. Whirlpools are water vortices.
