Dissecting a hurricane: What makes a superstorm?
| Miami
Days before hurricane Michael made landfall near Mexico Beach, Fla., in October, the National Hurricane Center predicted a remarkably accurate path, highlighting just how far scientists’ understanding of the storms has come. But Michael’s intensity still caught many Floridians by surprise, as it ramped up from a Category 2 to nearly a Category 5 monster in less than 24 hours. The Atlantic hurricane season officially ended on Nov. 30, but scientists find ways to study these storms year-round. Determined to figure out how to better predict the kind of rapid intensity change that was seen with Michael, one researcher has built a “hurricane in a box” in his laboratory on Virginia Key in Miami, Fla. With the touch of a button, University of Miami professor Brian Haus can turn a calm ocean scene in the 75-foot-long tank into a roiling Category 5 hurricane, complete with wind speeds topping 200 miles per hour and powerful waves. Living in Miami, “you really see the impact of trying to get better answers,” says Professor Haus. “If we got hit really badly, everything we know could be completely changed. And that makes you really want to try to understand this better.”
Why We Wrote This
For centuries, hurricanes have been viewed as chaotic forces of nature. Today, thanks to daring pilots and advancing technology, scientists and the public are gaining valuable insight into the making of a cyclone.
The first time a pilot intentionally flew an airplane into a cyclone, it was to settle a bet. When he emerged triumphant, he had not only proven that that the training airplanes used during World War II could survive the intensity of hurricane force winds; he had sparked an idea.
What if scientists could study a cyclone from the inside out? In the ensuing seven decades, hurricane research has taken off far beyond the dreams of those first storm chasers.
The Air Force Reserve now has a squadron dedicated to the daring trips, satellites snap spectacular images from aloft, and sensors on planes, ships, and satellites give forecasters the information they need to model a storm’s path.
Why We Wrote This
For centuries, hurricanes have been viewed as chaotic forces of nature. Today, thanks to daring pilots and advancing technology, scientists and the public are gaining valuable insight into the making of a cyclone.
That ongoing scientific investigation has fundamentally changed how we view hurricanes. The storms used to be seen as an inexplicable, destructive force of nature or an act of the gods. But now, we’ve begun to see hurricanes as something we can understand and predict.
Today meteorologists can forecast a hurricane’s track, wind speeds, rainfall, storm surge, and other details days in advance of landfall. “What we do now at five days [out], we dreamed of doing 20 years ago at two days,” says Ken Graham, director of the NOAA National Hurricane Center in Miami, Fla.
But there are still gaps in our knowledge of the details of hurricanes. And those nuances could prove crucial to making even more reliable forecasts. So even though the Atlantic hurricane season officially ended on Nov. 30., researchers find ways to study the storms year-round.
The making of a superstorm
One big question that still eludes hurricane scientists is how a hurricane goes from a disorganized tropical storm to a Category 5 monster overnight.
Such rapid intensity change was on clear display during hurricane Michael in October. The storm followed the path predicted by the National Hurricane Center several days ahead of landfall but caught people by surprise when, right before making landfall, the storm ramped up from a Category 2 to nearly a Category 5 storm in less than 24 hours.
Scientists have the big picture idea of the ingredients necessary for an intense hurricane. Warm ocean water, moist air, and consistent atmospheric winds all feed monster storms. And the opposite conditions can suck energy out.
But meteorologists’ models of rapid intensity change don’t always match the evolution of real storms. In the standard models, says Brian Haus, a professor in the ocean sciences department at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, “there’s just not enough energy getting up into the storm.”
Scientists think the gap in their understanding is strongly tied to what they still haven’t been able to see well: what happens where the atmosphere and the sea meet.
Planes can capture data from within the clouds, and satellites have revolutionized our view of the structure of the storms from above, but the air-sea interactions below are still difficult to observe. Ending up in the right place at the right time in the vast ocean with a ship or a buoy is tricky, and objects bobbing around in a hurricane are easily destroyed.
That’s why Professor Haus built a “hurricane in a box” in his laboratory in Miami. Inside the 75-foot-long clear box, water siphoned from nearby Biscayne Bay sloshes against a makeshift metal shoreline. With the press of a button, Haus can turn the calm ocean scene into a roiling Category 5 hurricane, complete with wind speeds topping 200 miles per hour and powerful waves. Sensors and cameras cover the hurricane simulator to capture the details.
Haus thinks something seemingly small may add a lot of fuel to ramp up a hurricane’s intensity rapidly: sea spray. The tiny water particles kicked up by breaking waves could be key, he says. Some research suggests that incorporating sea spray into models might yield better rainfall predictions.
The idea is that dramatic hurricane waves kick up a lot of sea spray, and those water droplets could be evaporating and rising up into the roiling clouds above. That water vapor can inject into the heart of the storm two of the three major intensification ingredients: moisture and heat. Using the hurricane simulator, Haus is taking a closer look at the characteristics of those water droplets flying through the air.
But a human-made hurricane isn’t the same thing as a real hurricane. Researchers are still trying to pierce the haze around real-life air-sea interactions during a hurricane by deploying more and better buoys and other tools during hurricane season.
Across the street from Haus’s laboratory on Virginia Key in Miami, at NOAA’s Hurricane Research Division, scientists and engineers are developing mechanical envoys to study the characteristics of the top of the ocean. One is a remotely operated vehicle, dubbed a glider, which looks a bit like a sleek narwhal. The gliders explore the top half mile of seawater for up to a month at a time, dipping down to various depths to take temperature, salinity, and other measurements before and during a hurricane.
Warmer water provides energy for a hurricane, while colder water draws energy from the storm, explains Ricardo Domingues, an oceanographer working on the gliders, which were first deployed in 2014.
“The key is to know how much heat is stored in the upper part of the water column,” he says, and if there are layers of colder water not far below. Turbulence from a hurricane overhead can bring that cold water up from the depths and weaken the storm. But the saltiness of seawater can act as a barrier to that mixing, he adds, so that is also crucial data to input into intensity predictions.
The human factor
Scientists aren’t the only ones who see hurricanes as much more knowable than in decades past. In hurricane country, the general public doesn’t simply rely on weather forecasts. Many residents pore over data and models put out by meteorologists about developing hurricanes and share satellite images of the storms on social media. More than 1.3 million people follow the National Hurricane Center’s Facebook page, and in Miami during hurricane season, Haus says, people can be overheard talking about the models – not just the storms – on the bus on the way to work.
But there’s still work to be done to make sure public perceptions of the risk of developing hurricanes are accurate, says the National Hurricane Center’s Mr. Graham.
“We’re not going to rest in trying to make the science better,” he says, “but the communication part of this is big. How do you communicate the risk so that people take the actions needed to save their lives?”
One challenge is that people’s perceptions of the risk of a hurricane often rely on their past experiences, explains Julie Demuth, a researcher at the National Center for Atmospheric Research studying risk perception. And, she says, “the devil’s in the details.” For example, if people decided to stay put during a Category 3 hurricane and saw no damage, they might think they can ride out future storms just as safely. But storms vary, from neighborhood to neighborhood – and from hurricane to hurricane.
“Hurricanes are like people. Every one is different,” says Frank Marks, director of NOAA's Hurricane Research Division. And as a result, he says, the current categorization process can be misleading. A Category 1 storm can cause a massively devastating storm surge when it makes landfall if it passes over shallow enough bodies of water. That's what happened when hurricane Florence hit North Carolina in September. Though it had approached the coast as a Category 4 storm, by the time it made landfall it had weakened to a Category 1 but still brought record-breaking storm surge.
“We need to change the narrative,” Graham says. “We need to really focus on those impacts independent of the category.” And that’s just what the National Hurricane Center is doing. For the past two years, for example, NHC has issued storm surge forecasts separate from hurricane forecasts.
For hurricane scientists and forecasters, getting it right is personal. Many live in hurricane-prone areas like Miami.
“You really see the impact of trying to get better answers,” Haus says. “If we got hit really badly, everything we know could be completely changed. And that makes you really want to try to understand this better.”
Forecasters also feel a sense of responsibility, Graham says: “The goal here is to protect lives.”
