Eager to get in on all the hurricane action, the British tabloid press screamed of “DOUBLE HURRICANE HELL” as weather models showed the remnants of Hurricanes Maria and Lee merging to form a “Giant Atlantic SUPERSTORM.”
Apart from the fact that, as you may suspect, this apocalyptic vision is somewhat oversold – it’ll just be a tad windy and wet over the UK for a day or two – it is actually possible for two hurricanes to merge.
There’s not much point in worrying about Maria and Lee, though; right now, they’re non-threatening Tropical Storms or just fairly insignificant depressions that will peter out over the next few days. What does happen when hurricanes collide, though?
Cyclonic mergers are described by the Fujiwhara effect, named after the Japanese meteorologist who first described such a phenomenon back in 1921, using water vortices as an example. When two cyclones get near each other, they will engage in a bit of ballet, pirouetting around each other either in a counterclockwise direction (in the Northern Hemisphere) or clockwise (in the Southern Hemisphere).
Eventually, they will begin to spiral in towards a central point. This happens for one of two reasons: either diverging winds essentially push them together, or because of something called positive vorticity advection, which describes how regions of high spin (hurricanes, for example) migrate towards areas of low spin (the space between the two).
The hurricane with a larger vortex – the more powerful one – will often dominate proceedings, and the smaller hurricane will dance around it for a bit, before falling into it. What happens afterwards, however, is uncertain.
Normally, the chaotic interaction of two entirely different tropical storms – whose outer winds are often going in different directions – means that the merger acts as a breaker force. This tends to reduce the singular entity’s overall strength and blasts it into weak remnants.
This is what appeared to have happened in 2001, when Hurricane Gill interacted with Hurricane Henriette; Gil was disrupted and broke up, but not before consuming the remnants of Henriette.