With the Atlantic hurricane season coming to its official end Saturday, scientists are already pondering the mysteries of what has been an extremely active six months.

It was also weird. So much so that Colorado State University researcher Phil Klotzbach called it "the strangest hyperactive season on record.”

The Atlantic spawned 11 hurricanes this season, above the annual average of seven. Also above average was the number of major hurricanes, defined as Category 3 strength or higher on the five-step Saffir-Simpson scale. There were five of those, compared to the three we’d expect to see in an average year.

It also included a number of costly storms that caused total economic losses of about $500 billion, according to early estimates from AccuWeather. But that’s not what made this season so strange, Klotzbach and other scientists said. Below are two key areas researchers are probing — and one twist on how 2025 may shape up.

Very quiet — then very active all at once

For the first time in more than 50 years, the Atlantic went silent during the heart of hurricane season. In an average year, there would have been four named storms between Aug. 13 through Sept. 8 — and at least two of them likely would have grown into hurricanes. Powerful storms like Hurricanes Andrew, Katrina, Laura, and Ida all formed during that period. But this year, not a single named storm spun up.

"I wouldn’t have believed it until I saw it,” Klotzbach said. "We’re trying to figure out exactly what happened and diagnose how much we can forecast that kind of thing in the future.”

That bizarre period of quiet was eventually shattered by a string of violent hurricanes, three of which took aim at the U.S. Southeast. Hurricane Francine broke the drought and struck Louisiana while Helene became a Category 4 and caused widespread destruction, killing at least 214 people throughout Appalachia and the Southeast after landfall in Florida’s Big Bend. A few days later, the monstrous Hurricane Milton briefly became one of the strongest hurricanes ever observed in the Atlantic basin as it churned toward the Tampa Bay region.

There are already theories about what caused those storms to become so powerful. Climate change is a top suspect, with the Atlantic Ocean running at record or near-record temperatures — nearly 90 degrees Fahrenheit (32 C) by the time Milton formed, compared to the 79 F threshold for a hurricane to form.

Decoding climate change’s exact influence

Those extra-warm waters loaded storms with additional energy, pushing their top wind speeds much higher than expected, according to a new study from researchers at the nonprofit Climate Central.

Without the influence of climate change, Hurricane Milton might have peaked at Category 4 strength before striking land, and Helene might have stayed a Category 3. Because wind speed is correlated with damages, lead author Daniel Gilford said, it’s fair to say that climate change made both storms more destructive.

"Category 5 and major hurricanes in general are increasingly becoming common in the North Atlantic,” Gilford said. "We see a consistent shift toward higher intensities, more intense major hurricanes, and that has us very concerned.”

There are likely other factors besides human-caused warming contributing to that upward shift in intensity, Klotzbach said, including some natural variability in ocean temperatures.

Next hurricane season’s wildcard

What’s not in doubt is that the Atlantic Ocean is at least 1 F to 3 F warmer than normal — and it’s stayed that way for the past 18 months. Winds that normally churn up the ocean and allow cool water to rise to the surface have been relatively quiet, Klotzbach said, adding that if the Atlantic holds onto its warmth over the winter, "it could mean the potential for another really busy season next year.”

One wildcard for 2025 is what happens with El Nino, a climate pattern that tends to dampen Atlantic hurricane activity by strengthening winds that can shred storms before they fully form. Its cousin, La Nina, has the opposite effect and has been on the cusp of emerging for months, which likely paved the way for stronger hurricanes over the Atlantic this past season.

Signs still point to a weak La Nina emerging before next spring, Klotzbach said. It’s hard to predict if La Nina would linger into the summer, but if it did, it would likely add further fuel to the 2025 hurricane season.

It’s also possible a spring La Nina could make a rapid transition back to El Nino, providing a slight headwind for hurricane season. "That would be unusual, but we’ve seen a lot of unusual stuff recently, so I rule out nothing at this point,” Klotzbach said.