Tropical cyclones could collide, triggering rare Fujiwhara Effect

Two tropical cyclones are barreling through the Atlantic on a potential collision course — and if they clash, a freak weather event merging them into one monster storm could wreak havoc along the East Coast.

Tropical Storm Humberto formed in the North Atlantic Ocean Wednesday and is expected to become a major hurricane this weekend, while another system looming in the Caribbean may strengthen into Tropical Storm Imelda in the coming days, according to Fox Weather meteorologist Greg Diamond. 

But if these two storms get too close, they could trigger the rare phenomenon known as the Fujiwhara Effect. 

What is the Fujiwhara Effect?

The wild weather anomaly — named after Japanese meteorologist Sakuhei Fujiwhara in 1921 — sparks when two cyclones come within 900 miles of each other and begin spinning around a shared center in what meteorologists liken to an erratic dance.

“The Fujiwhara Effect is when storms close together, interact, and rotate around each other,” Diamond told The Post Thursday. 

“Or simply, they dance around each other. For tropical systems, the two must be within 900 miles of each other. For ‘ordinary,’ non-tropical storms, they need to be within 1,200 miles of each other.” 

What happens next depends on each system’s size and strength — but in rare cases, they can smash together and create one giant super-storm, according to the National Weather Service.

However, if the storms are evenly matched, they’ll whirl around a shared point before breaking apart and fading — just like Pacific Hurricanes Hilary and Irwin in 2017.

In other cases — like Typhoon Hinnamnor clashing with a nearby tropical depression in the West Pacific in 2022 — the stronger storm can overpower and absorb the weaker one, Diamond explained.

Each scenario and storm interaction creates a huge forecasting challenge for meteorologists. 

The spectacle is rare in the Atlantic but happens more often in the West Pacific, Diamond said, noting there are no recent examples of storms colliding and causing land damage.

“This is mostly due to the West Pacific producing more tropical systems each year than the Atlantic,” he said. 

“When it does occur, it’s usually in the open ocean and far away from land.”

Tropical Storm Humberto forecast

Humberto, roaring through the Sargasso Sea with 50 mph sustained winds and moving northwest at 8 mph, is expected to become a hurricane by Friday night and rapidly intensify into a major Category 3 storm by early next week. 

The storm system currently poses no immediate threat to the United States, but residents in Bermuda are urged to track the forecast closely, Diamond warned. 

“There is high confidence that the center of Humberto will remain out to sea and away from the United States, posing no direct threat,” he said. 

“At most, some extra rain will be possible in the Carolinas due to a brief intrusion of moisture from the periphery of the storm. Residents in Bermuda will need to watch the forecast closely as it could impact the island next week.”

Imelda — currently known as Invest 94L — is a cluster of storms already pouring down on Puerto Rico, the Virgin Islands and Hispaniola, according to forecasters. 

Invest 94L could strengthen into a tropical storm or hurricane over the coming days, threatening the Georgia and Carolina coasts with damaging winds, life-threatening storm surge and heavy flooding starting Sunday, Diamond forecasted. 

He noted the storm could also be shredded by the mountains of the Dominican Republic, take longer to form, and stall over the Bahamas or near South Florida before heading offshore toward Bermuda. 

As for the chance of the two storms colliding, Diamond said it’s “not expected.”

“When it comes to Humberto and soon-to-be Imelda, the higher-odds scenario now is that the large upper-level low-pressure system and front that’s producing the rain from the Gulf Coast to New England will pick up likely-Imelda and pull it north,” he said. 

“If this happens, likely-Imelda and Humberto maintain enough distance from each other that they don’t ‘Fujiwhara.’”