Storms, Hurricanes, and Climate Change : Short Wave The end of the 2021 hurricane season was officially November 30. This year, there was a lot of hurricane activity. Today on the show, producer Thomas Lu talks to meteorologist Matthew Cappucci about this year's hurricane season — the ups, the lulls, and the surprising end. Plus — how climate change might be affecting these storms.

You can follow Thomas on Twitter @ThomasUyLu and Matthew @MatthewCappucci. Email Short Wave at ShortWave@NPR.org.

The 2021 Hurricane Season Wrapped

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EMILY KWONG, BYLINE: You're listening to SHORT WAVE from NPR.

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THOMAS LU, HOST:

Howdy, howdy, y'all. OK. The 2021 hurricane season officially ended on November 30, and there was a lot of activity.

MATTHEW CAPPUCCI, BYLINE: This year was a pretty busy season, not quite as bad as last year. But it's important to note that it only takes one storm to really leave a big impact.

LU: With so much that's happened in the water and on land, we thought it might be nice to do a hurricane wrap. I chatted with Matthew Cappucci. He's an atmospheric scientist. Well, actually, I'll let him introduce himself.

CAPPUCCI: I'm a meteorologist for The Washington Post, FOX 5 in D.C., for WAMU and pretty much everybody.

LU: So today on the show, we'll take a look at this year's hurricane season, the ups, the lulls and the surprising end. Plus, how climate change might be affecting these storms. I'm Thomas Lu, and you're listening to SHORT WAVE, the daily science podcast from NPR.

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LU: So, Matthew, can you start by defining, in simple terms, what is a hurricane versus a tropical storm or a depression?

CAPPUCCI: That's a great question. So all of these tropical cyclones start as clusters of thunderstorm activity.

LU: Right.

CAPPUCCI: And when thunderstorms are near each other, they start to interact. And over the tropics, the most efficient way for them to interact to work together is to have a common center. So all the air kind of goes in, goes up around that common center, sinks on the periphery of the storm and a little bit in that center. When you have something span multiple lines of latitude, it starts to spin because of the Earth's rotation. In the northern hemisphere, they spin counterclockwise. Eventually, they start sucking more and more air in, and that air accelerates faster as it approaches the center. When winds hit 39 miles per hour, it's designated a tropical storm, and it receives a name - when it hits 74 miles per hour, a hurricane. And from there, it can go up to major hurricane, and Category 5s have winds over 157 miles per hour.

So they do get pretty feisty. It's almost like, you know, Category 5s are essentially the strength of a tornado but over the open ocean. And perhaps the most impressive part is that hurricanes are born out of an abundance of calm, an abundance of peace because hurricanes need very calm winds in the upper atmosphere to form. They need a lack of temperature gradients, so change of the temperature with distance. It can't have much in the way of changing humidity. Everything needs to be kind of calm, peaceful, perfect and uniform. And it's amazing to think that the most tranquil conditions can give rise to the most furious conditions on Earth.

LU: So, Matthew, I know the hurricane season just ended not too long ago. How would you characterize the season in terms of the number of named storms?

CAPPUCCI: So this season was only the third time on record where we actually had to exhaust the entire name list, meaning we went through 21 named storms and really ran out of names. If we had gotten one more, we would have had to dip into the Greek alphabet in previous years. This year, they have a supplemental naming list that, for the first time, we would have had to gone into. Fortunately, we didn't have that, but needless to say, it was a very busy season.

LU: And it seems like there was a switch flipped. Right? Like, did we get a break from the storms?

CAPPUCCI: Yeah, it was really weird. So we ordinarily peak around mid- to late September, around the time when the water's the warmest...

LU: Right.

CAPPUCCI: ...When the wind dynamics are most favorable for storminess. And this year, like, we were busy all of September. And then after Victor in early October, we just kind of rapidly shut off - nothing for the rest of October. Wanda briefly developed towards the end of October, early November, and then since then, there's been nothing. And even Wanda was very weak. It was only a tropical storm in the middle of the Atlantic, mainly a fish storm. And to get, like, a complete sort of, like, a binary, if you will, of the season where one side is just completely hyperactive and the other side is next to dead, is pretty atypical, to say the least.

And one of the reasons was, of course, you had more sinking air towards the end of the season, which sort of squashed and suppressed the propensity for storm growth. But you also had a dramatic uptick in shear, or a change of wind speed and/or direction with height, that interrupted - kind of played a tug of war game with any storm that tried to get going. And so none of the seeds that were planted, so to speak, could actually bloom and materialize into storms. So early in season, very busy - second half, next to nothing. It was kind of too quiet.

LU: You mentioned a term earlier that I'm not familiar with, fish storms. Can you explain that?

CAPPUCCI: Oh yeah, that's just a colloquial term that meteorologists refer to when you have a storm passing over the open water that is doing everything a high-end hurricane would, but we're fortunate in that it avoids land. Like, we can look down on these storms via satellite and say, wow, that storm is really powerful. But otherwise, fish storms are storms that only affect the fish.

LU: And you've been following kind of storms and - through your work and your articles. What storms might we remember as far as ones that did significant damage, either to the U.S. or nearby countries?

CAPPUCCI: So there was one towards the middle of August that impacted Veracruz, Mexico, as a Category 3. That was Grace with 125 mile-per-hour winds. But the biggest one that really got all the headlines this year was Hurricane Ida, which hit Louisiana as a high-end Cat 4, almost a Cat 5, with winds of 150 miles per hour. Port Fourchon recorded a gust of 172, which is one of the highest gusts ever recorded in U.S. history anywhere. It's amazing we're actually able to do that without the whole observation station blowing away. But that one decimated southeastern Louisiana, just kind of ravaged the area with an impressive storm surge, very strong winds and killed dozens of people in southeastern Louisiana, both directly and indirectly.

But the storm really lived a second life in the northeastern United States, with a major tornado outbreak that produced 35 tornadoes across the Northeast, Mid-Atlantic, New England. And then that evening, September 1, all the moisture from Ida's remnants led to significant flooding across the Northeast. We got 3.24 inches in one hour's time at Newark International Airport. Central Park saw 3.15 inches. And keep in mind, that's the heaviest one-hour total either location has ever seen of rainfall. It was the rainiest day Newark has ever seen, with records dating back to 1930. It comes as no surprise that 43 people lost their lives in the Northeast due to that high-end flooding.

LU: Yeah, wow. That's a lot of rain, Matthew. And connected to this is climate change. You mentioned that there were so many storms that we ran out of names this year. But climate change is not necessarily about the number of storms, right?

CAPPUCCI: You're exactly correct. So we're actually forecasting a maintenance of the number of storms, if not a slight decline, over time thanks to climate change. But the storms that form should be significantly more intense going forward. What we're forecasting is that if the upper atmosphere and lower atmosphere warm at similar rates, there won't be much to spur more storms. But because the environment will be warmer, that means more rainfall, stronger winds, an increased chance of rapid intensification. So like we said, similar number of storms, maybe a few less, but those that form will be much higher end going forward. And we're already seeing that reflected in observed trends with a number of higher-end storms, major hurricanes we've had in recent years.

LU: So, Matthew, you mentioned rapid intensification. Let's start with that. In 2020, warm waters made for 10 hurricanes that intensified rapidly when speeds got 35 miles per hour faster on 24 hours or less, right? What happened this year?

CAPPUCCI: So this year, we saw that, too, with Hurricane Ida, which rapidly intensified. The bulk of the higher-end storms that we get do rapidly intensify. But Ida kind of waited until the last minute. We knew it would likely rapidly intensify. And we're waiting. We're waiting. We're watching. And then overnight, it went from this meager, you know, Cat 1, Cat 2 storm to very quickly a major hurricane with winds ultimately reaching 150 miles per hour at the time of landfall.

And this was something that 20, 30 years ago, we might not have been able to forecast. We're fortunate nowadays that we can, but it's still alarming to see a jump that quick in strength, especially because in the future, how are we going to be able to adequately plan for that, especially if it's not forecast? It's one of those things that if you live in a coastal city and you're trying to plan for something you see lurking off your coast, if it jumps from a tropical storm, a Cat 1 to a Category 4-plus in 30 hours' time, those are two completely different worlds of preparation.

So Kerry Emanuel is a professor of atmospheric sciences at MIT, and he did a great study a couple of years ago that looked into the frequency and intensity of rapid intensification and connecting that to climate change. He wrote that the incidents of storms that increase rapidly before landfall could increase substantially by the end of the century, which, again, is really tough to predict. And even if we're getting better at saying where the storms are going, if we're getting caught off guard by how quickly these storms are rapidly, quickly strengthening, it's going to spell major impacts on our coastal infrastructure and, really, our society.

LU: So is it - I guess is it appropriate to say that climate change is, in effect, supercharging our storms?

CAPPUCCI: Most definitely. So we're getting stronger winds from these storms. And my biggest concern is also heavy rainfall, because for every degree Fahrenheit the air temperature increases, the air can hold 4% more water. Now, if you have an entire atmosphere's worth of warming, suddenly, it reflects in, like, a 15% increase at times in how much moisture a hurricane or tropical storm is holding. That, and we're noticing kind of a slowdown in storms as they approach the coast.

But when you have slower-moving storms that dump more moisture, that's a recipe for flood disasters. Look at what happened in Houston back in 2017 with Hurricane Harvey or in 2019 with Tropical Storm Imelda. As it was dumping the bulk of its moisture, you had 45 inches worth of rainfall causing damage, injury fatality and wreaking havoc in the Golden Triangle of Texas and Louisiana, an area that was hard-hit just two years prior. And it's getting to a point where we kind of have to redraw the lines, redraw the textbooks of how often extreme rainfall will occur in those areas. And heavy rainfall is one of those things that a lot of people underestimate in the context of tropical cyclones.

LU: Yeah, yeah. I appreciate you bringing up rainfall because you're right. I think when we talk about hurricanes and we talk about storms, a lot of our focus is, how fast are the winds, right? We don't necessarily think about the rainfall. When we're forecasting hurricanes, why do we focus on just the winds when, clearly, rain is such a significant and important part of this, as well?

CAPPUCCI: Because we are stubborn, stubborn people.

LU: (Laughter) OK.

CAPPUCCI: As an industry, as meteorologists, as atmospheric scientists, we are stubborn. We latch on to something, and we keep it that way. We latched onto the Saffir-Simpson Hurricane Scale decades ago, and it's been that way ever since. Really, hurricanes in terms of the wind impact have a very small footprint, but it also makes for the most visceral imagery, the most kind of compelling TV and radio and newspaper articles, whereas flooding is something that is, like, a slow-motion disaster but causes much more - you know, flooding causes five times more deaths just from fresh-water flooding. Look. You can drive away from wind. You can drive a few miles inland - you'll be good. You can't drive away from rainfall. Rainfall - if you look at Hurricane Florence, for example, back in 2018, that occurred across the entire Carolinas. People all the way to the Piedmont were very much impacted by rainfall. It's tougher to escape rainfall, and I think a lot of people underestimate just the potency of that.

LU: How would you drive home the message that, yes, the winds are important, but also definitely also consider the rain?

CAPPUCCI: I think we're getting better at it with time, but we need to shy away from using this Category 1, Category 3, Category 5, Category whatever because that is only predicated on the wind speed, nothing else. And I strive to partition threats. I strive to write a piece about the rainfall threat, the wind threat, the this threat, the whatever threat, so people know what they're up against.

LU: Right, Matthew, we've talked a lot about climate change. We've talked about the technology, the forecasting, how it affects the public and how we can be better at messaging. We've even did a little roundup of this year. Do you have any final words or last thoughts or anything you want to say?

CAPPUCCI: I think we're getting to the point where people are going to need to question if the property that they are buying is the type of property they're going to want to inhabit in 20, 30, 40 years. Is that the best place to be next time? Because especially nowadays, there will be a next time. It's not a matter of if. It's a matter of when. And with recurrence intervals shrinking, meaning these things are becoming more frequent and more intense, especially in vulnerable areas, we're going to want to change our infrastructure. One of the unfortunate things that has a silver lining with hurricanes is that when infrastructure is destroyed, it gives us the beautiful chance to build it back better, stronger and more resilient. And we're just not doing that. And it really makes me sad because every hurricane is an opportunity to build stronger communities, and we just don't do it.

LU: All very interesting points. Thank you for that.

CAPPUCCI: Well, thank you again so much for taking the time.

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LU: This episode was produced by Eva Tesfaye, edited by Gisele Grayson and fact-checked by Margaret Cirino and Rasha Aridi. The audio engineer was Patrick Murray. I'm Thomas Lu. Thanks for listening to SHORT WAVE, the daily science podcast from NPR.

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