History is unfolding in the Atlantic Ocean right now. Hurricane Melissa has spun up into an extraordinarily dangerous Category 5 storm with maximum sustained winds of 175 mph, and is set to strike Jamaica Monday night before marching toward Cuba. This is only the second time in recorded history that an Atlantic hurricane season has spawned three hurricanes in that category. Melissa has already killed at least three people in Haiti and another in the Dominican Republic.
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The threats to Jamaica will come from all sides. The island could see up to 30 inches of rain as the storm squeezes moisture from the sky, like a massive atmospheric sponge, potentially causing “catastrophic flash flooding and numerous landslides,” according to the National Hurricane Center. Melissa also will bulldoze ashore a storm surge of up to 13 feet — essentially a wall of water that will further inundate coastal areas. “No one living there has ever experienced anything like what is about to happen,” writes Brian McNoldy, a hurricane scientist at the University of Miami.
It will take some time for scientists to determine exactly how much climate change supercharged Melissa, but they can already say that the storm has been feeding on warm ocean temperatures made up to 800 times more likely by global heating. This is how climate change is worsening these tropical cyclones overall: The hotter the ocean gets — the seas have absorbed 90 percent of the extra heat that humans have pumped into the atmosphere — the more energy that can transfer into a storm. “The role climate change has played in making Hurricane Melissa incredibly dangerous is undeniable,” Marc Alessi, a climate attribution science fellow at the Union of Concerned Scientists, said in a statement.
Scientists can already estimate that climate change has increased Melissa’s wind speeds by 10 mph, in turn increasing its potential damage by 50 percent. “We’re living in a world right now where human-caused climate change has changed the environment in which these hurricanes are growing up and intensifying,” said Daniel Gilford, a climate scientist at the research group Climate Central. “Increasing temperatures of the atmosphere is increasing how much moisture is in the atmosphere, which will allow Melissa to rain more effectively and efficiently over the Caribbean, and could cause more flooding than otherwise would have occurred.”
Making Melissa extra dangerous is the fact that it’s undergone rapid intensification, defined as a jump in sustained wind speeds of at least 35 mph in a day, having doubled its speed from 70 to 140 mph in less than 24 hours. This makes a hurricane all the more deadly not only because stronger winds cause more damage, but because it can complicate disaster preparations — officials might be preparing for a weaker storm, only to suddenly face one far worse. Research has shown a huge increase in the number of rapid intensification events close to shore, thanks to those rising ocean temperatures, with Atlantic hurricanes specifically being twice as likely now to rapidly intensify.
At the same time, hurricanes are able to produce more rainfall as the planet warms. For one, the atmosphere can hold 7 percent more moisture per degree Celsius of warming. And secondly, the faster the wind speeds, the more water a hurricane can wring out, like spinning a wet mop. Accordingly, hurricanes can now produce 50 percent more precipitation because of climate change. “A more intense hurricane has stronger updrafts and downdrafts, and the amount of efficiency by which the storm can rain basically scales with how intense the storm is,” Gilford said. Making matters worse, Melissa is a rather slow-moving storm, so it will linger over Jamaica, inundating the island and buffeting it with winds.
As Melissa drops rain from above, its winds will shove still more water ashore as a storm surge. The coastlines of the Caribbean have already seen significant sea level rise, which means levels are already higher than before. (Warmer oceans have an additional effect here, as hotter water takes up more space, a phenomenon known as thermal expansion.) All of this means the baseline water levels are already higher, which the storm surge will pile on top of. “Just small, incremental, marginal changes in sea level can really drive intense changes,” Gilford said.
Jamaica has an added challenge in its mountainous terrain. Whereas water will accumulate on flat terrain, it behaves much more unpredictably when it’s rushing downhill because it easily gains momentum. “When you get a storm like this that is approaching the higher echelons of what we have observed, it’s harrowing, especially because it is pointing at a populated island with complex terrain,” said Kim Wood, an atmospheric scientist at the University of Arizona. “You’re dealing with a funneling effect, where that water, as it falls, will then join other water that’s coming down the mountainside and exacerbate the impacts.”
Maybe the only good news here is that the National Hurricane Center was able to accurately predict that Melissa would rapidly intensify. And in general, scientists have gotten ever better at determining how climate change is supercharging hurricanes, so they can provide ever more accurate warnings to places like Jamaica. But that requires continuous governmental support for this kind of work, while the Trump administration has slashed scientific budgets and jobs. “We couldn’t do this without continued investment in the enterprise that supports advances in not just science, but forecasting and communicating the outcomes of those forecasts,” Wood said.
This article originally appeared in Grist at https://grist.org/extreme-weather/how-hurricane-melissa-got-so-dangerous-so-fast/.
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