Here’s what can happen when two hurricanes get too close together

By CNN Meteorologist Mary Gilbert, CNN

(CNN) — Hurricanes and other systems don’t often find themselves in a tropical traffic jam in Earth’s vast oceans, but there are consequences when they do get all up in each other’s business.

A tropical tango known as the Fujiwhara effect can unfold when two storms move too close together and start to influence one another’s strength and track.

That scenario has a chance to play out off the southeastern US coast later this weekend or early next week.

The first storm, Tropical Storm Humberto, formed Wednesday afternoon a few hundred miles east-northeast of the eastern Caribbean. Humberto is expected to reach hurricane status Friday and keep strengthening into next week. The second is a stormy area moving over the northern Caribbean that could become a tropical depression this weekend and potentially Tropical Storm Imelda not long after.

These two systems could end up within arm’s reach of each other early next week, with their centers as little as several hundred miles apart, if early predictions hold. That’s very close quarters for storms of this size and is precisely when Fujiwhara comes into play.

The Fujiwhara effect explained

Back in 1921, Japanese meteorologist Sakuhei Fujiwhara published a paper that theorized two storms spinning near each other could start rotating together around a common center point. He was proven correct.

Think about it like the final round of musical chairs: two kids circle the same chair until the music stops. The Fujiwhara effect essentially describes that dance, playing out on a much bigger scale.

Exactly how close they need to be to trigger the Fujiwhara effect varies based on the size of each storm. Generally, Fujiwhara can begin when two large storms — those that span hundreds of miles — get within at least 850 miles of each other, according to the National Oceanic and Atmospheric Administration. That distance shrinks to about 350 miles for smaller storms.

The resulting interaction unfolds differently depending on the strength of both storms.

Two closely matched storms will orbit around a common point for a while and eventually go their separate ways. The circling tugs each storm off the path they would have taken if the other storm wasn’t there.

East Pacific hurricanes Hilary and Irwin experienced this version of the Fujiwhara effect in 2017. Hilary was a bit stronger than Irwin, but they were overall decently well-matched to start. Both systems interacted for so long, they eventually dissipated around the same time.

But if one storm is much stronger than the other, it could absorb the energy of the weaker one as they spin — and ultimately consume it.

This exact scenario played out in the West Pacific Ocean in 2022. Powerful Typhoon Hinnamnor was headed right for Taiwan before it crossed paths with a tropical depression that was trying to strengthen.

The Fujiwhara effect kicked in, and Hinnamnor and the depression interacted and rotated until the typhoon devoured the depression. Hinnamnor slowed down as a result, which left it open to disruptive winds that weakened it for a bit, but it restrengthened and took a nearly 90-degree turn from its original track.

In especially rare Fujiwhara scenarios, two weaker or smaller storms spinning together could merge and create one larger storm, according to the National Weather Service.

All of these potential interactions and outcomes pose an incredible forecasting challenge, even for computer forecast models. Any small changes in the expected strength or size of each storm, or slight deviation from the anticipated tracks throw a model’s complex calculations into chaos.

It’s still a toss up if Humberto and potential future Imelda will in fact share a dance card in the coming days, or if the Fujiwhara interaction models are predicting doesn’t become a reality. Given all this uncertainty, it will be key to keep a close eye on the forecast heading into next week.

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