Hurricane Melissa shows a troubling new normal for major hurricanes
Hurricane Melissa, which made landfall in both Jamaica and Cuba over the past two days, followed what has unfortunately become a familiar pattern for major storms in a warming world.
The most catastrophic storms – those accompanied by the most intense winds and torrential rains – were once rare, but are becoming increasingly likely due to climate change. Similarities also appear in the behavior and timing of these powerful hurricanes.
Before Melissa hit Jamaica as a Category 5 monster, it was blowing through particularly warm waters, like other hurricanes over the past decade. This allowed it to strengthen at a meteoric rate, becoming the most powerful of this year’s Atlantic season and tying the record for the strongest landfall ever recorded in the Atlantic.
Then the storm slowed, giving it more time to dump rain on Jamaica, another hallmark of hurricanes on a warming planet. Melissa’s timing was also remarkable: It formed late in the season—hurricane activity is generally thought to peak in early September—while ocean heat persisted into the fall.
Taken together, this behavior makes Melissa something of a model for the new hurricane normal, experts say.
“These storms are not the same as they were 20 or so years ago,” said Shel Winkley, a meteorologist at the nonprofit research group Climate Central.
It’s a change with life-saving consequences – one that forecasters and managers in storm-prone areas are now watching closely.
Step up in a hurry
One of Melissa’s most telling characteristics is how quickly she escalated. In just 18 hours, it went from tropical storm status to Category 4 on Sunday, before reaching Category 5 early Monday.
Climate change increases the risk of this “rapid intensification” pattern, which the National Hurricane Center defines as an increase in sustained wind speed 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 humidity in the atmosphere caused “extremely rapid intensification.”
“We’ve gotten very good at forecasting and understanding when hurricanes are going to significantly increase in intensity, but with Melissa, it’s surpassed even the best forecast we can do in terms of wind speeds,” 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 seem like much when it comes to a giant hurricane, but small temperature differences can really have a big impact,” Winkley said.
Many other recent storms have experienced rapid intensification. Last year, Hurricane Milton’s wind speeds increased by 90 mph in about 25 hours, and in 2022, Hurricane Ian experienced two cycles of rapid intensification before making landfall in Florida. The list goes on: Hurricanes Idalia in 2023, Ida in 2021, and Harvey in 2017 also experienced rapid intensification.
Fewer hurricanes, higher impact
Over the past 35 years, the number of hurricanes and tropical cyclones that form each year has decreased.
“We see that the number of hurricanes worldwide, including typhoons, has declined significantly since 1990,” said Phil Klotzbach, an atmospheric scientist who studies hurricanes at Colorado State University.
But this overall decrease is largely due to a drop in cyclone activity in the Pacific, Klotzbach said; Hurricane activity in the Atlantic has increased, primarily due to 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 develop, they are more likely to develop into major storms as the seas warm.
“We have seen an increase in the number of people reaching categories 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 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 in high-altitude winds that can prevent or destroy hurricanes. Those winds could strengthen in some places and weaken in others, he said: “It’s not a very simple answer.”
How these trends will manifest remains an active area of research and scientific debate.
A longer hurricane season
It did not escape experts that the most powerful hurricane of the season struck just days before Halloween.
“We’re pretty late in the season at this point. Things should start to calm down,” said Derrick Herndon, a researcher with the University of Wisconsin’s Tropical Cyclone Research Group.
The Caribbean has always been a hot spot for powerful late-season hurricanes, but they’re becoming even more likely, Klotzbach said — he recently submitted research showing the trend to peer review. At the same time, hurricane data in the era of satellite observations (1971 to 2022) suggests that the hurricane season also begins earlier in the year.
The fall hurricane pattern was 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 warm, paving the way for storms in late October and early November, he said: “That stacks the dice in favor of these robust hurricanes.” »
Hurricane Melissa was exacerbated by warmer-than-usual waters off the southern coast of Jamaica.
“If you’re going to have a really intense hurricane in the Atlantic, it’s probably going to be in that part of the world,” Herndon said.
In the past, such a storm would typically have kicked up cold water below the surface and stifled its own growth, according to Andy Hazelton, a hurricane modeler and associate scientist at the University of Miami’s Cooperative Institute for Marine and Atmospheric Studies. But this year, ocean heat is high at the surface and up to 200 feet deep, he said, so Melissa simply produced more heat and energy.
The storms stop
Just before or after making landfall, hurricanes are now more likely to stop and dump immense amounts of rain, according to a study published last year. Other research suggests that their speed of advancement has become slower overall, although this remains a matter of debate.
Hurricane Melissa followed the same pattern, stalling off the coast of Jamaica as it continued to gain intensity. On Tuesday morning, the day it first made landfall, the storm was moving at around 3 km/h. Forecasters expected up to 30 inches of rainfall in parts of Jamaica, more than a third of its annual average.
Scientists have not reached a consensus on why some storms move more slowly, but some have speculated that it is because climate change has weakened atmospheric circulation patterns.
Hurricane Harvey in 2017 was a dramatic example of the consequences of such a blockage: When it parked over Houston, the storm dropped about five feet of rain in some places. This pattern is particularly problematic because a warmer atmosphere can absorb and deliver more precipitation.
“For every degree Fahrenheit of warming, the atmosphere can hold 4 percent more humidity,” Winkley said. “Warmer oceans not only increase the intensity of hurricanes, but they also allow more evaporation, which leads to more rain-producing moisture in the atmosphere for these hurricanes to absorb and then release.”
