Fujiwhara effect: Can 2 hurricanes merge into a megastorm?

The Atlantic hurricane season has become even more active, with multiple storms churning away at once. If two storms get close enough, could they merge into one?

Often, the smaller of the two systems will begin to orbit around the larger storm before the two systems go their separate ways, according to the National Weather Service.

That sort of circling interaction between two storms is known as the Fujiwhara effect.

If the centers of the systems come within 680 miles of each other, though, they could actually merge into one larger storm.

The conditions have to be just right for that to happen, though.

“Albeit common, the Fujiwhara effect is very unstable,” explained Oreste Reale, a research meteorologist at NASA’s Goddard Space Flight Center. “The two vorticity maxima must be at a certain distance and reach some sort of temporary balance. If one of the two has a drastic change – for example, the lower levels become affected by drag so that the storm enters a rapid weakening – the Fujiwhara effect rapidly vanishes.”