As hurricane season ends, researchers note its surprises

Three Category 5 storms, one of the most powerful hurricanes on record, no U.S. landfall, and a mystifying lull in the usual peak of activity: Together, these and other factors have resulted in a “wacky” hurricane season this year.

In any case, that’s what atmospheric specialist Phil Klotzbach says.

“It was just a strange year,” said Klotzbach, who studies hurricanes at Colorado State University. “A pretty difficult year to characterize.”

Hurricane season officially ends on November 30. In some ways, 2025 is what researchers expect to see more often as the climate warms: Hurricanes continued to form late in the season, and several intensified at extreme rates to produce some of the most intense storms in history.

But in other ways, it was just strange. Fewer hurricanes formed than experts expected, but almost all developed into major storms. And the continental United States was spared for the first time in a decade. These surprises are a reminder of the unpredictability of hurricane season – especially in a warming world – even as forecasts become more accurate.

Fewer hurricanes, higher intensity

National Oceanic and Atmospheric Administration forecasters predicted an above-average season in May with six to 10 hurricanes. Of those, at least three are expected to be major storms, meaning Category 3 or higher, with sustained winds of at least 111 mph.

Klotzbach made the same forecast independently, and other hurricane tracking groups were in the same situation.

Ultimately, fewer hurricanes formed, but of the five that did form – Erin, Gabrielle, Humberto, Imelda and Melissa – four were considered major.

“This is the highest ratio ever recorded in the last 50 years,” said Brian McNoldy, a hurricane researcher at the University of Miami’s Rosenstiel School of Marine, Atmospheric and Earth Science.

Additionally, three of these major storms were Category 5, the highest level of intensity.

Forecasters’ predictions of an above-average season proved accurate despite fewer storms due to a measure called accumulated cyclone energy — essentially a calculation of the overall intensity and duration of all tropical storms during a season.

Klotzbach predicted that the accumulated energy would be 125% of the 30-year average. The season was 108% complete, which, given the low number of hurricanes, means each one packs a punch.

“It was a quality season, not a quantity season,” he said.

Nine of the last 10 Atlantic hurricane seasons have been above normal, according to Klotzbach, who attributes the trend to high ocean temperatures and La Niña, a seasonal circulation pattern that tends to weaken the high-altitude winds that discourage hurricane formation.

McNoldy, who closely tracks water temperatures in the Atlantic, said 2025 would have been “abnormally warm.”

“Whatever the storms were, they certainly had plenty of fuel to exploit,” McNoldy said. Heat from the oceans drives evaporation, causing warm, moist air to rise from the surface to create convection; Hurricanes require ocean temperatures of at least 79 degrees Fahrenheit to form.

High sea temperatures have allowed several hurricanes to gain intensity at a rapid pace. Erin’s maximum sustained wind speed increased by about 75 mph in just 24 hours. Melissa went from a tropical storm to a Category 4 hurricane in the same time frame.

Both are “really, really exceptional” rates of intensification, McNoldy said.

Melissa also tied the Labor Day hurricane of 1935 as the strongest storm on record. Both had sustained winds of 185 mph and Melissa saw a gust of 252 mph.

A strange lull during rush hour

Despite fuel from the ocean’s hurricanes, this season has sometimes lacked spark. Storm activity usually peaks in late August and early September, but not this year, McNoldy said: “For about three weeks at the height of the season, it was completely dead.” »

Nothing significant formed in the Atlantic between August 24 and September 16, according to Klotzbach. This hasn’t happened since 1992.

Although the lull is similar to the slowdown seen last year, researchers don’t think it will become a trend.

“The fact that we’ve had two quiet peak seasons in a row is certainly strange, but I think it’s just a coincidence,” McNoldy said.

The reason for last year’s lull was that tropical storms developed too far north to cross the Atlantic and pick up steam, according to Klotzbach. During this year’s break, the eastern Atlantic was relatively stable and dry, conditions not conducive to the formation of powerful storms.

A big near miss

No hurricanes made landfall in the United States this year for the first time in a decade, according to Klotzbach.

But this would not have been the case if Hurricane Imelda had not taken a sharp turn.

As Imelda headed toward the United States as a tropical storm in September, forecasters thought the Carolinas could receive buckets of rain. But Hurricane Humberto, a Category 5 monster that was moving several hundred kilometers out to sea, pushed Imelda away from the coast.

This phenomenon is known as the Fujiwhara effect: when two storms orbit a common midpoint, the weaker storm is often swallowed up by the stronger one.

“If Humberto hadn’t been there, Imelda probably would have been a big flood story,” Klotzbach said.

As McNoldy says: “Another crazy part of the season. »

AI predictions are promising

In the National Hurricane Center’s written forecasts during Hurricane Melissa, a new term kept appearing: “Google DeepMind.”

Federal forecasters are increasingly relying on the new artificial intelligence-based hurricane forecasting tool, which was instrumental in early prediction of the rapid intensification of Hurricane Melissa.

Google DeepMind has built an impressive resume during hurricane season, McNoldy said. Recently, he evaluated forecast error levels in more than 10 hurricane models and found that DeepMind was among the best.

“It was a model that was just introduced to the public in June, and it outperformed other conventional models in terms of track and intensity, which is unheard of, to have something new and this good,” McNoldy said. “It’s hard not to be optimistic about this.”

This article was originally published on NBCNews.com