The new face of major hurricanes

Hurricane Melissa, which made landfall in both Jamaica and Cuba in the last two days, followed what has unfortunately become a familiar pattern for major storms in a warming world.

The most catastrophic storms — those with the most intense winds and soaking rains — were once rare, but they are becoming more likely because of climate change. And similarities are emerging among these powerful hurricanes’ behavior and timing, too.

Before Melissa hit Jamaica as a Category 5 monster, it churned over especially warm waters — as did other hurricanes over the past decade. This allowed it to strengthen at blistering pace, becoming the most powerful of this year’s Atlantic season and tying the record for strongest landfall ever in the Atlantic.

Then the storm slowed to a crawl, giving it more time to dump rain on Jamaica, another hallmark of hurricanes on a warming planet. Melissa’s timing, too, was notable: It formed late in the season — hurricane activity has typically been thought to peak in early September — as ocean heat lingered into the fall.

Taken together, this behavior makes Melissa a kind of poster child for the new normal of hurricanes, experts said.

“These storms aren’t the same storms as a couple decades ago,” said Shel Winkley, a meteorologist at the nonprofit research group Climate Central.

It’s a shift with life-or-death consequences — one that forecasters and officials in storm-prone areas are now watching closely.

Intensifying in a hurry

One of Melissa’s most eye-opening characteristics is how remarkably fast it intensified. In just 18 hours, it exploded from a tropical storm into a Category 4 Sunday, before reaching Category 5 strength early Monday.

Climate change is increasing the risk of this “rapid intensification” pattern, which the National Hurricane Center defines as an increase in sustained wind speeds of at least 35 mph over 24 hours.

In Melissa’s case, Winkley said, unusually warm sea-surface temperatures in the Caribbean and high levels of moisture in the atmosphere caused an “extreme rapid intensification.”

“We’ve gotten really good at forecasting and understanding when hurricanes are going to make a big boost in intensity, but with Melissa, it even exceeded the best forecast that we can make for it in terms of wind speed,” he said.

Winkley added that the storm passed over Caribbean waters that were 2.5 degrees Fahrenheit warmer than usual — conditions that climate change made up to 700 times more likely.

Two-and-a-half degrees Fahrenheit may not sound like a lot when it comes to a giant hurricane, but small temperature differences can really make a big impact,” Winkley said.

Many other recent storms have undergone rapid intensification. Last year, Hurricane Milton’s wind speed increased by 90 mph in roughly 25 hours, and in 2022 Hurricane Ian went through two rounds of rapid intensification before making landfall in Florida. The list goes on: Hurricanes Idalia in 2023, Ida in 2021 and Harvey in 2017 all underwent rapid intensification, too.

Fewer hurricanes, higher impact

In the past 35 years, the number of hurricanes and tropical cyclones that form annually has been decreasing.

“We find that the number of hurricanes globally, including typhoons, has gone down significantly since 1990,” said Phil Klotzbach, an atmospheric scientist who studies hurricanes at Colorado State University.

But that overall decrease is largely due to a drop in cyclone activity in the Pacific, Klotzbach said; Atlantic hurricane activity has risen, primarily as a result of a decades-long trend toward La Niña, a seasonal circulation pattern that tends to weaken the high-altitude winds that discourage hurricane formation.

“La Niña is good for the Atlantic if you like hurricanes,” Klotzbach said.

When hurricanes do develop, they’re more likely to turn into major storms as the seas warm.

“We’ve seen an increase of those reaching Category 4 and 5,” Klotzbach said.

Melissa was the third Category 5 hurricane this year — the first time in two decades that more than two storms of such power have formed in the same season.

Zachary Handlos, an atmospheric scientist at Georgia Tech University, said that although warmer seas in the future will be more conducive to hurricanes, a warmer atmosphere will force changes to the high-altitude winds that can prevent or destroy hurricanes. These winds could strengthen in some locations and weaken in others, he said: “It’s not a very straightforward answer.”

How these trends will play out remains an active area of research and scientific dispute.

A longer hurricane season

It’s not lost on experts that the strongest hurricane of the season hit just days before Halloween.

“We’re pretty late into the season at this point. Things should be starting to wind down,” said Derrick Herndon, a researcher in the Tropical Cyclone Research Group at the University of Wisconsin.

The Caribbean has always been a hotspot for powerful, late-season hurricanes, but they’re becoming even more likely, Klotzbach said — he recently submitted research showing the trend for peer review. At the same time, hurricane data in the era of satellite observations (from 1971 to 2022) suggests that hurricane season is beginning earlier in the year, too.

The fall hurricane pattern has been fueled by the long-term trend toward the La Niña pattern, Klotzbach added, which itself is likely the result of a combination of climate change and natural variability.

La Niña weakens high-altitude winds at a time when Caribbean waters are still hot, setting the stage for storms in late October and early November, he said: “It loads the dice toward these robust hurricanes.”

Hurricane Melissa was exacerbated by warmer-than-usual waters off Jamaica’s southern coast.

“If you’re going to get a really intense hurricane in the Atlantic, it’s going to probably be in this part of the world,” Herndon said.

In the past, such a storm would typically have churned up cold water from below the surface and stifled its own growth, according to Andy Hazelton, a hurricane modeler and associate scientist with the University of Miami’s Cooperative Institute for Marine and Atmospheric Studies. But this year, ocean heat is elevated both at the surface and as deep as 200 feet below, he said, so Melissa simply churned up more heat and energy.

Storms are stalling

Just before or after landfall, hurricanes are now more likely to stall and dump immense amounts of rain, according to a study published last year. Other research suggests their forward speed has gotten slower overall, though this remains a topic of debate.

Hurricane Melissa followed the pattern, stalling off the coast of Jamaica as it continued to build intensity. On Tuesday morning, the day of its first landfall, the storm was moving at just around 2 mph. Forecasters expected up to 30 inches of rainfall in parts of Jamaica, which is more than a third of its annual average.

Scientists have not reached a consensus about why some storms are moving more slowly, but some have theorized that it’s because climate change has weakened atmospheric circulation patterns.

Hurricane Harvey in 2017 was a dramatic example of the consequences of such stalling: When it parked over Houston, the storm dropped about 5 feet of rain in some locations. The pattern is particularly problematic because a warmer atmosphere can absorb and deliver more rainfall.

“For every 1 degree Fahrenheit of warming, the atmosphere can hold onto 4% more moisture,” Winkley said. “Warmer oceans not only boost the intensity of hurricanes, but it allows for more evaporation, so it’s putting more of that rain-making moisture into the atmosphere for these hurricanes to absorb and then unleash."

This article was originally published on NBCNews.com