Fujiwhara Effect

When two hurricanes spinning in the same direction pass close enough to each other, they begin an intense dance around their common center. If one hurricane is a lot stronger than the other, the smaller one will orbit it and eventually come crashing into its vortex to be absorbed. Two storms closer in strength can gravitate towards each other until they reach a common point and merge, or merely spin each other around for a while before shooting off on their own paths. In rare occasions, the effect is additive when the hurricanes come together, resulting in one larger storm instead of two smaller ones.

One example of this (below) was between hurricanes Hilary and Irwin in the East Pacific in 2017.

GOES-16 satellite imagery over the eastern Pacific Ocean from July 25 to August 1. Hurricane Irwin on the left collided with Hurricane Hilary on the right; the two merged before fading out over the ocean.