Space.com:

"Red Spot Jr." as it is being called, formed after three white oval-shaped storms—two of which were at least 90 years old—merged between 1998 and 2000.

A similar merger took place centuries ago and formed the bigger and legendary Great Red Spot, a storm twice as big as Earth and almost 300 years old.

Little is known about how storms form on the giant planet. They are often described as behaving similar to hurricanes on Earth.

The global change cycle began when the last of the white oval-shaped storms formed south of the Great Red Spot in 1939. As the storms started to merge between 1998 and 2000, the mixing of heat began to slow down at that latitude and has continued slowing ever since.

The movement of heat from the equator to Jupiter's south pole is expected to stop at 34 degrees southern latitude, where Red Spot Jr. is forming.