In late September, a pair of tropical cyclones danced across the Atlantic Basin. To the left is Tropical Storm Imelda, which at the time was moving northward above the islands of The Bahamas. To the right is Hurricane Humberto, which was moving northwest approximately 700 miles (1,100 kilometres) east of them. Imelda brought hazardous tropical storm conditions to Puerto Rico, Cuba, the northern Caribbean, and Bermuda; and there were severe weather warnings issued across the US East Coast. Its floodwaters resulted in four deaths in the Dominican Republic. However, the relative proximity of Humberto may have saved lives.

When two cyclones pass close to each other, spinning in the same direction, they can start to ‘dance’ around their common centre, with the smaller and weaker cyclone orbiting around the larger one. Eventually, the two cyclones will either merge into a single larger cyclone, or else they will continue on their own paths. This interaction between two cyclones is known as the Fujiwhara effect.

Cyclones subjected to the Fujiwhara effect can be unpredictable, which makes forecasting them particularly difficult. But the dance can sometimes work in our favour. In this instance, Humberto pulled Imelda away from the land and out onto the dancefloor of the sea. This likely spared the US East Coast from widespread and dangerous flooding.

Tropical Storm Imelda and Hurricane Humberto above the Bahamas spotted by the VIIRS (Visible Infrared Imaging Radiometer Suite) on the Suomi NPP satellite on September 28, 2025.