It’s only February, but sea surface temperatures in the Atlantic Ocean are already hitting early summer levels, a worrying trend that could indicate an active hurricane season ahead — or another marine heat wave.

Brian McNoldy, a senior research associate at the University of Miami, called this early season heat “very, very exceptional,” and said it’s a strong sign that the upcoming hurricane season could see an above-average number of storms.

In the North Atlantic, he said water temperatures are running three months ahead of schedule, at May-level temperatures. In the main development region of the Atlantic, where most hurricanes are born, McNoldy said sea surface temperatures are closer to July levels.

“That is like hurricane season out there right now,” he said. “We’re just blowing past all the other years, there’s no comparison.”

But hurricane season doesn’t start until June 1, leaving plenty of long weeks of heating between now and the official start date. High sea surface temperatures are closely connected with more storm formations and an earlier start to the season. Scientists have suggested that climate change-driven warming has pushed the start of the hurricane season above two weeks earlier, to mid-May.

Last year, the record-breaking heat of the Atlantic won out over the historically storm-dampening effects of an atmospheric phenomenon called El Niño. This year, El Niño is fading fast and the majority of NOAA models predict we’ll see its sister phenomenon, La Niña, by hurricane season. La Niña is known to reduce storm-shredding wind shear in the Atlantic, making it easier for storms to form.

The combination of a coming La Nina and an already warm ocean likely spells an active season, McNoldy said.

“Once we do start seeing the early season forecasts from Colorado State University and NOAA, I suspect they’re going to be pretty aggressive,” he said.

And a hot ocean doesn’t just mean more storms. Last year’s ocean temperatures led to a record-breaking marine heat wave in the Caribbean. Scientists said it had never gotten so hot, so early. At one point, a shallow water area in Florida Bay registered a hot-tub level temperature of 101 degrees Fahrenheit.

And coral reefs largely paid the price.

While a full accounting is still underway, early results show that out-planted nursery corals (not the older, native reefs) died in massive numbers. A survey released last week found some nursery reefs with a 100% death rate, prompting the nonprofit that manages it to pause all coral transplantation for the 2024 season.

The extreme heat prompted NOAA to add new colors to its coral bleaching warning scale this year. Previously, the scale went from “no stress” to “alert level 2,” an open-ended category that meant severe, widespread bleaching and death were expected on local reefs.

Starting this year, there are three more categories — in three darker, more worrying shades. The new highest category, Alert Level 5, means scientists expect “near complete mortality” of the reefs, where more than 80% of corals in the area could die.

The change in scale to reflect a worsening environment is reminiscent of how Hurricane Harvey’s unprecedented rainfall rewrote the rainfall projection maps. After soaking Houston with nearly 50 inches of rain, scientists added new colors and new levels to their rain maps.

There’s also the controversial push to classify new “Category 6” hurricanes as climate change makes it more likely that stronger storms form.

While scientists have more clearly tied climate change to Harvey’s extreme rain and stronger hurricanes, the marine heat wave likely has multiple causes, McNoldy said.

The ocean is definitely warming, NOAA records show, as a result of the unfettered burning of fossil fuels heating up the atmosphere. But experts say it’s unlikely that climate change alone could cause a dramatic one-year shift in sea surface temperatures like we saw last year.

McNoldy said he noticed that the trade winds that blow across the Atlantic and cool the water’s surface are weaker than usual, just like last year, which could contribute to the hotter temperatures. Another factor scientists are discussing is the lower amount of air pollution floating over the Atlantic.

After cargo and cruise ships were ordered to burn cleaner fuel, they stopped spewing as many particles of pollution into the atmosphere over the Atlantic. NOAA research suggests that clearer skies meant fewer clouds, hotter water, and potentially even more hurricane formation.

For now, McNoldy said, the exact cause of the weirdly warm Atlantic is unknown.

“What’s going on? How are we getting such ridiculous outliers? The North Atlantic became record-breakingly warm on March 6 last year and hasn’t stopped since. We’re just about at a full year of record-breaking warmth nonstop, and I don’t totally know why,” he said.

“When are we going to get back to normal? Or is that gone?”