It was a tango of two tempests, a waltz over the waters of the Atlantic—and it saved the U.S. East Coast from a direct hit by a potentially catastrophic storm.
Hurricanes Humberto and Imelda were so close to one another when they churned in the Atlantic basin at the same time in September that they danced around each, the bigger and more powerful Humberto steering Imelda away from the coast.
It's called the Fujiwhara effect, a meteorological phenomenon in which two storms orbit around a shared center point, influencing each other's intensity and track and sometimes merging. Japanese meteorologist Sakuhei Fujiwhara first documented the interaction between vortices in the early 1920s.
It is just one example of what has so far been an unusual 2025 Atlantic hurricane season. With less than two months before it ends, the season stands out not only for what has occurred (the relatively rare Fujiwhara effect) but also for what has not occurred: For the first time in 10 years, no hurricane had made landfall in the U.S. by the end of September.
Now, the season enters the homestretch. And while random chance, or simply put, good old-fashioned good luck, has operated in our favor, don't think for a second that we're in the clear. Troubled waters, researchers warn, could lie ahead.
"We absolutely cannot leave our guard down," said Lynn "Nick" Shay, a professor of oceanography at the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science.
Shift in storm activity
In a historical sense, Shay is spot on. Though the intertropical convergence zone—a thunderstorm belt of low pressure near the equator—has retreated south, reducing the frequency of tropical waves from Africa that spawn long-track storms, the Caribbean Sea and Gulf of Mexico are now poised for an uptick in storm activity, he said.
"Caribbean and Gulf storms usually develop late season compared to those that form from waves off Africa," explained the researcher, who investigates warm-water eddies that break off from the Loop Current in the Gulf and supercharge hurricanes. "By the time we get to late September and October, atmospheric conditions such as low wind shear and an abundance of moisture, and of course sea surface temperatures and ocean heat content levels, hit their peak in those regions. And it's that combination that makes the Caribbean and Gulf ripe for potential storm development this time of year."
Could the U.S., then, see its first landfalling hurricane soon? Perhaps, Shay said.
Saharan dust has diminished, he noted, and upper-level steering currents now tend to favor storms as the Bermuda high, a high-pressure system over the Atlantic that influences the track of tropical storms, shifts westward, pushing systems over the northwest Caribbean and Gulf. "And once they are in those areas, hurricanes will make landfall in stark contrast to what we have seen so far in the western Atlantic with hurricanes generally curving away from the U.S. Eastern Seaboard."
And October is "historically the busiest month for South Florida in terms of hurricane activity," said Andy Hazelton, an associate scientist at the University of Miami Cooperative Institute for Marine and Atmospheric Studies (CIMAS).
"Storms during that time typically don't come from the east. They come from the south or the southwest—south of Cuba over the Caribbean and then moving to the northeast," he said. "We haven't had one of those in a while. Wilma was the last big one." Hazelton was referring to Hurricane Wilma. While storms have occurred in late October, Wilma was the last late October storm to make landfall in the state, doing so on Oct. 24, 2005.
"So, we'll need to be vigilant as we get into the middle part of October," Hazelton said.
Still an active season
While it has been quiet in terms of landfalling storms in the U.S. and abroad, the season has been active when other aspects are considered, according to Brian McNoldy, a senior research associate and tropical cyclone expert at the Rosenstiel School.
"There have been 11 named storms, four hurricanes, and three major hurricanes," he said. "Climatologically, by Oct. 10, there would be 11 named storms, five hurricanes, and two major hurricanes. And impressively, there have already been two Category 5 hurricanes this season—Erin and Humberto—and in the past century, only eight other seasons have had two or more Category 5 hurricanes form."
McNoldy, the co-author of a paper that documented the merger of Hurricane Gil and Tropical Storm Henriette in the East Pacific in 2001, also noted the accumulated cyclone energy, or ACE, a metric used to measure the overall activity of a hurricane season. "Rather than counting storms, it integrates the duration and intensity of whatever storms there were. So, one long-lived hurricane can contribute much more to the tally than several weaker storms," he said, noting that, as of the publication of this story, the ACE index was about 92 percent of average for the date, a figure that will surely change when Tropical Storm Jerry, currently spinning in the Atlantic, becomes a hurricane, as forecasters expect.
Hurricane hunters flying high
As such, the National Oceanic and Atmospheric Administration (NOAA)'s Hurricane Hunter aircraft have remained busy, flying into the heart of storms and deploying high-tech tools such as dropsondes and drones to collect vital storm data used by forecasters at the National Hurricane Center to issue advisories.
NOAA's two P-3 Orion turbo prop aircraft and its Gulfstream IV jet flew a combined 13 missions into Hurricane Erin. While that long-lived and powerful Cape Verde storm, the first Category 5 cyclone of the season, never made a U.S. landfall, it still created havoc, spawning dangerous rip currents, high surf, and flooding in several states.
Jason Dunion, a meteorologist at CIMAS and with NOAA's Hurricane Research Division, served as the on-ground science director for those flights. He later flew on missions into Hurricane Gabrielle, collecting valuable data for forecasters and also conducting research that will help understand how storms behave.
"Whenever possible, we always tack on research to our operational missions," Dunion said. "We were able to fly on a series of pure research missions into Gabrielle, testing new technology that will help diagnose how storms become titled and how that positioning can affect their intensity. Of course, we send such information to forecasters. But we'll go into research mode in the offseason to really pick that data apart and get a better understanding of how storms act."
