Dear Tom,
Gustav is heading toward the U.S. with Hanna following. Have two tropical cyclones
have ever run into each other?
Bob Freed Naperville
Dear Bob,
When two tropical cyclones get close to each other (less than a thousand miles), they
do not collide, but rather rotate around each other cyclonically (counterclockwise in the
Northern Hemisphere), a result of the Fujiwhara effect. This motion is named after the
Japanese meteorologist Sakuhei Fujiwhara who described it in a 1921 paper dealing
with the motion of whirls in water. A classic example of the Fujiwhara effect took place
in August 1995 when Tropical Storm Iris was interacting with Hurricane Humberto. With
time, the storms often drift apart and move their separate ways, but if one is
significantly stronger it may eventually absorb the other storm into its circulation.
