Last month, forecasters watched in horror as Hurricane Melissa lumbered across the Atlantic Ocean, transformed into a monster and targeted the Caribbean islands. As predicted by the National Hurricane Center, the landfall was catastrophic: while authorities are still calculating the costs, both in lives lost and property destroyed, at least 67 people were killed in Jamaica, Cuba, Haiti and the Dominican Republic. AccuWeather estimates the damage at $50 billion.
Even before the storm hit Jamaica and continued its journey north, scientists were explaining how climate change helped turn the hurricane into an exceptional Category 5 storm with winds of 300 km/h: the warm waters it used as fuel were 900 times more likely due to global warming, helping to increase wind speeds by 16 km/h.
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Today, the research group World Weather Attribution crunched the numbers in its own report, similarly finding that human-caused warming increased the tropical cyclone’s maximum wind speed by 11 mph — a seemingly small amount that can actually increase damage exponentially — and its extreme rainfall by 16 percent. Overall, this climate change has increased the likelihood of these conditions sixfold. “This study found that all aspects of this event have been amplified by climate change, and that we will see the same thing as we continue to burn fossil fuels,” Ben Clarke, report co-author and research associate at Imperial College London, said on a press call Wednesday.
Gathering that kind of strength requires three main ingredients. On the one hand, these storms like humidity, because dry air discourages their formation. Second, they need an atmosphere free of vertical wind shear or winds moving at different speeds and in different directions at different altitudes. And finally, they need warm ocean water to transfer energy from the sea to the sky.
Not only did Melissa pass through unusually warm waters, but she crawled over it at a relatively slow speed, between 1 and 3 mph, “allowing the storm to gather immense destructive energy,” the report notes. The ocean was also temperate well below the surface, so when the hurricane buffeted the sea it absorbed more fuel. (Colder conditions at depth lead to upwelling that reduces the amount of fuel available. In this case, you can actually see a path of colder waters left by a storm – a sort of snail’s trail – like Hurricane Erin did last year.)
What happened in the Caribbean days before the landing stunned scientists. A hurricane “intensifies rapidly” when the maximum sustained wind speed increases by at least 35 mph in one day, and it experiences “extremely rapid intensification” when it jumps 58 mph during that time. Melissa blew well past that threshold, doubling from 70 to 140 mph in just 18 hours. Indeed, studies have shown that Atlantic hurricanes are now twice as likely to intensify rapidly, and scientists have seen an explosion in the number of these events near coastlines. This phenomenon is particularly dangerous because local authorities might prepare for a more tame tropical cyclone, only to face something much more devastating.
Even if some infrastructure could survive the wind, there was no escaping another consequence of these gales: the storm surge that washed ashore. This caused water levels in Jamaica to rise up to 16 feet, devastating coastal communities. Here too, climate change is making the situation worse, as such a deluge adds to already higher sea levels. Additionally, warmer waters take up more space than colder waters, which is called thermal expansion.
How Hurricane Melissa Became So Dangerous So Quickly
The precipitation was also even more catastrophic. The milder the atmosphere becomes, the more moisture it can hold, which is part of the reason why extreme precipitation is getting worse around the world. Plus, the faster a hurricane’s winds blow — and again, Melissa’s reached 185 mph, which is about as fast as they do — the more water it can pull from the sky. Indeed, the report notes that five-day heavy rainfall in Jamaica, like that associated with Melissa, is about 30 percent more intense and twice as likely in today’s climate. For eastern Cuba, this increase is more of the order of 50 percent.
The landscape itself made the situation worse, as Melissa’s extreme rainfall cascaded down the mountains and valleys, accelerating under its own weight. Worse still, it had rained in Jamaica before the storm arrived, so the Earth could not absorb more water to avoid flooding. “The slow movement of the storm caused destructive conditions to persist for many hours, with extreme rainfall, hurricane-force winds and sustained storm surges over extended periods of time,” Jayaka Campbell, report co-author and climatologist at the University of the West Indies in Jamaica, said at the news conference.
However, thanks to advances in hurricane science, forecasters were able to accurately predict Melissa’s rapid intensification, giving everyone a good idea. This allowed Jamaica to open 881 emergency shelters and preposition supplies, while Cuba evacuated 735,000 people from coastal and low-lying areas.
“If there’s a silver lining to this storm, it’s that we live in a time where we have good forecasts for hurricanes,” Roop Singh, manager of urban issues and attribution at the Red Cross and Red Crescent Climate Center and co-author of the report, said on the call. “It is likely that this saved many lives. At the same time, it is important to note that people have no living memory of such a severe storm, making it more difficult to adequately prepare.”
