Neighboring storms do everything from “tango” to merging into a single cyclone.
Every June through November, NOAA reminds the public that whenever a hurricane hits the coast, it becomes an active Hurricane season. But can you imagine two hurricanes hitting at the same time? On rare occasions, two tropical cyclones can actually track each other close enough to form a pair—a phenomenon known as the Fujiwara effect.
The phenomenon takes its name from the Japanese meteorologist Sakurahira Fujiwara, who is thought to have first described this hurricane interaction around 1920.
History buffs will appreciate the fact that the first observed instance of two hurricanes merging occurred during World War II, when Typhoons Ruth and Susan “Postponed General MacArthur’s planned landing of occupying forces in Japan in 1945. This phenomenon occurs only once or twice a year in the waters of the western North Pacific, and even less in the North Atlantic basin, about once every three years.
The most recent Fujiwara interaction was observed in April 2021 when Tropical Cyclone Thurroga fully absorbed Tropical Cyclone Odjet off the coast of Western Australia.
How does the Fujiwara effect happen? em>
Lots of fortuitous events can encourage Fujiwara interaction. For example, if a basin is particularly active, tropical cyclones can concentrate in a particular area of the ocean. Troughs and ridges in the upper atmosphere act as barriers on hurricane tracks and can also guide storms along similar paths, increasing their chances of crossing paths.
Even the speed of individual storms can lead to encounters. Fast-moving hurricanes can run ahead, catching up to storms that formed days ago, while slow or stationary hurricanes can sway in place, waiting for passers-by.
While each of the above scenarios contributes to placing two tropical cyclones side by side, the physical distance between them determines whether they will interact. To have this effect, they have to be close enough to each other — a distance of about 900 miles or less, which is the length of the state of California. Once two hurricanes are adjacent and spinning so close together, one of several things can happen.
When storms of equal intensity meet p>
When twin cyclones are of equal strength, they typically orbit the central region of the ocean between them in a manner that orbits Rossi.
Eventually, they will either have an “elastic interaction” in which they drop everything and continue on their separate paths, or they will coalesce into a single storm.
When a strong storm meets a weak storm< /p>
If one hurricane surpasses the other in strength and size, the two storms will still “dance”, however, the weaker storm will usually orbit the stronger storm.
When this rotation occurs, the larger cyclone tears off part of the adjacent smaller cyclone, weakening it slightly (a process known as “local stretching”) “). That’s what happened during the 2010 Atlantic hurricane season, when Category 1 storm Julia and major Hurricane Igor pinched too closely. Igor’s outflow battered Julia for several days before it weakened to tropical storm status.
Larger cyclones can also weaken smaller ones to the point of dissipation (“full tension”). When this happens, the smaller cyclones usually disappear into the atmosphere, but the dominant storm can also partially absorb the weaker storm, growing slightly as a result.
While the idea of twin tropical cyclones is troubling, meteorologists stress that superstorm scenarios should not be expected — at least, not like Earthstorm, The Day After Tomorrow and other disaster movies. A small number of hurricane interactions resulted in the merger of the two storms. Even when storms merge, their effects are rarely additive. That is, a Category 2 storm and a Category 3 storm do not necessarily combine to form a Category 5 storm.
Coastal dwellers and vacationers should be aware, however, that Storm Fujiwara may cause last-minute changes in the storm’s track, as each storm affects the movement of the other . That means less opportunity to prepare before the storm makes landfall.