Fujiwhara

The Fujiwhara effect is a rare phenomenon that sees nearby cyclones ‘dancing’ round each other. In July it was seen not once, but twice*: Hurricanes Hilary and Irwin rotated round each other in the Eastern Pacific Ocean off the coast of Mexico generating high surf for Southern California; whilst thousands of miles away in the western Pacific east of Japan just days earlier, Typhoon Noru and Tropical Storm Kulap spun round each other*.

The Fujiwhara effect describes the rotation of two nearby - within about 1,200km - storms around each other and a common midpoint (anti-clockwise in the northern hemisphere).

The Fujiwhara effect was named after Sakuhei Fujiwhara, who described a paper about symmetrical motions in the atmosphere in 1921