Short Wave - Hurricane Helene Is Here And Powerful

Episode Date: September 27, 2024

Governors across the southeastern United States have declared statewide states of emergency as Hurricane Helene continues its ascent. After forming in the northwestern Caribbean Sea Tuesday, Helene escalated from a tropical storm, then to a cyclone, and finally to a Category 4 hurricane by the time it made landfall late Thursday night. We talk to hurricane climatologist Jill Trepanier about how a storm tropical storm system rapidly intensifies into a major hurricane, the impact of a changing climate on future storms — and why the devastation doesn't stop at the shore.Follow local updates on Hurricane Helene.Want to know more about the scientific underpinning of serious weather events? Email us at [e-mail] — we might cover it on a future episode! See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Hurricane Helene is here. After forming in the Northwestern Caribbean Sea Tuesday, it escalated into a powerful storm. We are bracing for the worst. We know that there's going to be a lot of damage. We know there's going to be a lot of destruction. At a category four, it's a major hurricane. And the largest and most intense to ever hit Tallahassee, the capital of Florida.

In an interview with NBC, Mayor John Daly said the city has been preparing for days. We have called in our mutual aid agreements and we have crews that are driving through the night as far away as Oklahoma to come help out. Upon landfall, Hurricane Helene brought a storm surge of as much as 20 feet to the Florida Panhandle before traveling up towards Georgia and Tennessee. And when we called up Jill Chippanier Thursday, she reminded us the ratings of tropical cyclones from tropical depressions to Category 5 hurricanes. is all about the wind. When they hit certain levels of wind speed, which are sustained winds within a system, so not just a gust, we hit tropical storm,

then Category 1, 2, 3, up to 5 on the Safier-Simpson scale. When you hit Category 3 or major category levels, there's a good chance that you'll start seeing major uprooted trees, structural damage to homes. And the scale itself is exponential. So a five is significantly worse than what a one is. Jill's a hurricane climatologist at Louisiana State University. She says Helene was able to get up to such a powerful category so quickly

because of abnormally hot waters in the Gulf of Mexico. It's one of the causes of what's known as rapid intensification. Rapid intensification refers to a 35-not-winds. speed increase in 24 hours. And 35 knots is approximately 40 mile per hour jump. And this major category hurricane level of category three, four, and five hurricanes, in order to get to that incredible level of wind speed, some of them undergo at three, four different times. And Helene isn't wholly unusual in this pattern. Large, powerful storms. are more likely when they form over hotter ocean water,

and climate change is causing ocean temperatures to rise. Plus, hurricanes are causing more severe floods because of the combined effects of higher seas and heavier rain. Today on the show, how Helene turned into a major hurricane and why there's much more to a powerful hurricane than the winds that categorize them. I'm Regina Barber, and you're listening to Shortwave, the science podcast from NPR.

Okay, Jill, Hurricane Holmber. Helene went from a tropical storm to a hurricane Wednesday morning, and it made landfall as a category four. And Helene isn't the only storm that's gotten significantly more powerful before landfall. About three quarters of major hurricanes that form in the Atlantic undergo this increase in wind speed. So what are the ingredients for like this rapid intensification for a tropical storm? The major ingredient that is present in virtually all of the rapidly intensifying events is an incredibly warm ocean surface. That is not the only ingredient that is required. And the others vary across differing events, which is why it makes it difficult to know exactly if a storm will or will

not rapidly intensify. But we're getting better with every passing year, with each one, it provides us a series of data. We don't want them to happen. It would be better for them not to happen and we don't get the data. But the small silver lining of an event like this is it provides us more information than we had before that we can then put into our calculations, into our understandings and discussions to try to better predict the next one. Okay, so we talked to you a little more than a year ago and you told us that we need to observe a large number of storms to be able to connect rapid intensification to climate change. Why is that? With any past, season, even during an ice age. I'm going to go kind of backward a little and think about a period of time where we're not actively warming. The equatorial zone or the tropical belt of our planet receives a surplus of energy from the sun. It has more direct line of radiation. And so it allows more energy to exist there as a product of that. That energy has to move. It doesn't stay at the tropics. It moves. That's what the wind blowing literally is, is energy transfer.

So if there is a surplus of energy, it may create a major category hurricane and move that energy. It may have multiple small hurricanes that move that energy, right? And if we think about a planet with an increased surplus of surplus energy, we then have this space of, are we going to start to see more of those higher category storms or more frequent events? because both are possible. And I think for understanding whether or not a rapidly intensifying signature by one storm is related to climate change, it's much more about the group of them as a whole. Are they reaching higher categories more often than what they did in the past? And then the more we have, again, not just individually helps us predict, but then collectively helps us understand

how it might be related to a systematic shift in what's happening in our Earth system. Okay. I mean, let's talk about, like, that rain, too. Like you're saying, other things that happened from the storm. So when Helene arrived, it was 85 degrees Fahrenheit in the Gulf of Mexico. That's super warm water. Can you lay out the connection between very warm water and heavy rain? Yes. Okay. So there is a direct relationship with the amount of energy present in the atmosphere and the amount of water that can also be present as a vapor within that temperature. So there's a direct relationship between air temperature and the amount of water that it can move. So if we have really warm air, then we also see very large cloud structure. It's a really good indication that there must be an incredible amount of water present to actually build those clouds in this warm climate to then make it rain. So all else being equal, the hotter the air,

the more water it can move. And so if we think- Fatter the clouds. The fatter the clouds. Absolutely. And sometimes what a lot of the research has been supporting is higher intensity rainfall. So not necessarily longer duration, not necessarily you know, a higher coverage of rainfall, though that is a different part of research that is also being supported, but more high intensity rainfall. So when it rains, it pours. And so bring it back to this idea of what does that ocean temperature kind of add to this. It provides a continuous fuel source for moving energy from the open ocean surface through evaporation and then condensing it in the upper atmosphere to release that energy to really make that cloud continue to grow. Okay, so what does this

mean? Like, what does it mean for these inland areas to have this hurricane like hundreds of miles from where the storm makes landfall? Like, how is this rain going to affect people? So that's a really great question. You are correct that the expectation is often it is a coastal phenomenon and that is only where we need to be worried about it is at that coast where it's making landfall. This particular storm, all storms, they have a forward motion. They're moving through space. Some of them stall, like Hurricane Harvey did, over Houston, to dump all of that rain that it's carrying in one place. But with Helene and others that we've seen, it has quite a fast forward motion. And so it's moving through the landscape fairly quickly. This is both good and bad. It is good for the people

at the actual coast because then the conditions are up and out. They've exited relatively quickly so that they can begin recovering from what just happened, which is certainly more detrimental at the coast. But then bad for those that are living much farther inland, that then the storm continues to move quickly and release all of this moisture that it has been carrying over that landscape. So it's this important idea that you think that the storm actually has a life cycle and it's not done yet even just because it hit the coast. It will carry with it until its final demise, if you will, then it rains itself out and you've brought that moisture to new places. So I would suggest anyone in that inland track space well beyond the center of the storm. Be mindful of your local weather service offices.

Have those alerts available on your phone. Make sure they're turned up. So that way, you're just mindful of what your own world is. And it's very important. Turn around. Don't drown. Do not drive into flooded waterways. Find another way around.

That's really important. Okay. Last question. As a hurricane climatologist, what will you be monitoring specifically after landfall? A few things. One of them is storm surge. Right along the local coast, I actually have quite a few friends and fans. family that live throughout Florida. And so I'm watching for them. General power outages,

I would expect most of Florida will be without power, as well as South Georgia as it moves through. How long are they without power? That's a really important piece of the puzzle. So we often see linemen coming in, line people coming in from neighboring states, even from the north that make their way down to get them back online because power makes everything easier. And because if power takes too long, that's when the resources really need to start flowing in, right? This idea of adequate water resources, food for people to eat, even just, you know, making sure those that need to be involved with Red Cross are, I think down to trees, that's a big piece of that puzzle. And then generally, how far inland did that storm surge make it into Florida? Because that's going to change how disastrous it could be.

I hope that your friends and your family are safe. Thank you very much. Up and out. That would be good. Up and out. Yeah. Thank you so much for talking to us today. You're very welcome.

It was my pleasure. If ever I can help you again in any other way, please just let me know. Oh, we will. This episode was produced by Hannah Chin and edited by our showrunner Rebecca Ramirez. It was fact-checked by Rebecca, Rachel Carlson, and Tyler Jones. Robert Rodriguez was the audio engineer. Bet Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Regina Barber.

Stay safe out there. And thank you for listening to Shorewave from NPR.