The Fujiwhara effect is a meteorological phenomenon that occurs when two nearby tropical cyclones or low-pressure systems begin to rotate around a common center, like a dance. This "dance" can have several outcomes: the storms may orbit each other, the stronger storm may absorb the weaker one, or the two storms might merge into a single, more powerful system. The interaction is named after Japanese meteorologist Sakuhei Fujiwhara, who first described it in 1921.
Several factors can influence the occurrence of the Fujiwhara effect. First, the two systems need to be within 900 miles of each other. One system has to be significantly less intense than the other. Two systems of similar strengths will likely undergo a power struggle and ultimately go their separate ways. Size is also a key factor. The larger system typically takes the "win," as the smaller system will orbit the larger one, and then the larger storm absorbs the smaller system. Atmospheric conditions, such as wind shear, ocean temperatures, and atmospheric pressure, influence how the storms interact.
Although the Fujiwhara effect can occur anywhere the correct parameters and conditions are present, it is more common in the Pacific, where tropical cyclones are more abundant. In the Atlantic, it is uncommon to have two low-pressure systems in proximity.
When the Fujiwhara effect occurs, it has significant implications. First, a storm's track can change or even stall. Additionally, as a storm intensifies, it can potentially bring greater impacts to the area it threatens. Considering the track can change, there may be many with less warning time.
When has it happened most recently?
In 2017, a well-documented Fujiwhara effect occurred in the Eastern Pacific between Hurricane Irwin and Hurricane Hilary. You can clearly see that in this case, they both orbited around, merged, and then dissipated as they moved north. It was a tough battle between them, as they were both hurricanes, making it a rarer occurrence.
In the Atlantic, there was another Humberto that went through the Fujiwhara effect. In 1995, Hurricane Iris and Hurricane Humberto moved in tandem, but Iris absorbed Humberto, leading to a stronger system.
Plenty of moisture is available, and conditions will become more favorable for two systems to receive names late this week and into the weekend.
— Florida Public Radio Emergency Network (FPREN) (@FloridaStorms) September 24, 2025
Could there be a Fujiwhara effect? ... maybe. pic.twitter.com/uXCSIcD41Z
Could this happen between Invest 94 (or future Imelda) and Humberto?
It certainly can. Humberto will be slowing down between Thursday and Friday, and this could give Invest 94 time to exit the Caribbean and move over the southern portion of the Bahamas. Humberto is forecast to remain well offshore, at a safe distance from the United States' eastern coastline, but it can absorb Imelda if the parameters and conditions align well enough. The best situation for Florida could be for Humberto to absorb Invest 94 (or Imelda, if it receives a name), as this would push it farther away from the state. Additionally, an upper-level low will be shielding Florida and much of the southeastern United States. If it dips south enough at the right time, then it will give it a little extra nudge toward Humberto, helping the matter.
