EMILY KWONG, HOST:
You're listening to SHORT WAVE...
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REBECCA HERSHER, BYLINE: Hey, Emily Kwong.
KWONG: Hey, Rebecca Hersher, NPR climate desk correspondent. How are you?
HERSHER: I'm great. Also, it's hurricane season again.
KWONG: Yeah. You know, it happens every year.
HERSHER: It happens every year. It catches me by surprise every year.
KWONG: Yeah.
HERSHER: And, you know, most years, I end up talking to you about it...
KWONG: Yeah.
HERSHER: ...Because there's so much science in hurricanes, especially as the climate changes and especially this year, honestly, because this year is - groan-worthy pun - a bit of a perfect storm situation for hurricanes in the Atlantic.
KWONG: On the contrary, I'm not groaning. I'm a little nervous to hear this. What's up with the Atlantic?
HERSHER: It's not good, but it's also weirdly interesting.
KWONG: Does this perfect storm situation have something to do with all the hot weather we've been having? Like, June has been toasty.
HERSHER: Infernal...
KWONG: Yeah.
HERSHER: ...Is the word I would use. Yeah. No, it totally does have something to do with that. So the high temperatures on land but also in the ocean play a big part, although there's definitely more to the story, including a bit of a scientific mystery that is unfolding in the Atlantic right now.
KWONG: Well, let's get into it. So today on the show, the Atlantic hurricane forecast for this year is more active than ever. We get into the science behind that forecast and how to prepare if you live in a hurricane-prone area.
HERSHER: Which - newsflash - is, like, half of the United States. Everyone lives in a hurricane-prone area. I mean, not everyone, but a lot of people.
KWONG: Could be you. So keep listening to SHORT WAVE, the science podcast from NPR.
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KWONG: All right. Rebecca Hersher, esteemed colleague, NPR climate correspondent.
HERSHER: (Laughter) Yes, Emily.
KWONG: So the Atlantic hurricane season, it's already begun. June 1 is when it kicked off, right?
HERSHER: Yeah. So we're a few weeks in, and we're just seeing our first storm right now actually, which is pretty normal. Hurricane season usually starts out slowly in the Atlantic and really gets going in the late summer and early fall.
KWONG: And you said earlier forecasters are predicting a record-breaking number of storms. So, like, how many storms are they foreseeing?
HERSHER: Potentially more than two dozen. The National Hurricane Center is predicting between 17 and 25 storms will form in the Atlantic this year. And at least eight of those are expected to be full-blown hurricanes, as opposed to, you know, weaker tropical storms. At least four of those are expected to be major hurricanes. So major hurricanes, that means category three or above, if you're familiar with the categories. So that means really powerful winds that can uproot trees, destroy mobile homes and damage other buildings.
KWONG: Is this a lot more than average? Like, what is the - what's the normal number of storms?
HERSHER: Yeah. It's actually the largest number of storms that the Hurricane Center has ever predicted at the beginning of a hurricane season.
KWONG: Oh.
HERSHER: The average number of storms in a season is only 14.
KWONG: And they're saying more than two dozen.
HERSHER: Could be.
KWONG: OK.
HERSHER: Could be.
KWONG: So why so many storms? Also, how do they even predict how many storms are going to happen in a whole season?
HERSHER: Great question. So, yeah, it's statistical forecasting, right? So they're using math, the same way forecasters can tell you that it's going to be a snowier-than-average winter probably or that it's likely to be a rainier-than-average spring. That's how they're able to do these predictions for a whole season. And the temperatures being so hot is one of the reasons that forecasters are predicting so many storms this year.
You know, human-caused climate change is driving up temperatures around the world, not just on land - like so many of us are experiencing firsthand this week - but in the ocean, where the hurricanes form. Water temperatures in the Atlantic are abnormally high. And I talked to Gavin Schmidt about this. He's a climate scientist at NASA.
GAVIN SCHMIDT: They've been in record-breaking territory for almost the entire last 12 months.
KWONG: Oh, 12 months, so basically for a year.
HERSHER: Yeah. Yeah. And actually, preliminary data that came out since I talked to Gavin show that it's probably 13 months at this point, so more than a year.
KWONG: That's a lot of months in a row to be breaking records for ocean heat.
HERSHER: Yeah. Yeah. And the temperatures are off the charts. I mean, all this extra heat in the ocean, it is, like, fuel for hurricanes. It helps them get big and powerful, which is one reason there are so many storms forecast - right? - because disturbances that might have just stayed as minor storms are more likely to grow into full-blown tropical systems if the water is really warm when they form. And abnormally hot water and air also makes storms wetter because the warm air can hold more moisture, which then falls as heavy rain when the storm hits land.
KWONG: We've talked before on SHORT WAVE about how rain - it's actually the most deadly part of a hurricane. It's what happens after it all falls.
HERSHER: Yeah. Yeah, exactly. Flooding from rain is actually responsible for the most hurricane deaths in the U.S., and it can affect people really, really far from the coast as well.
KWONG: So, Rebecca, why is the ocean itself so hot? And is that what climate scientists were expecting to happen as the Earth heats up from climate change?
HERSHER: Well, so yes and no. And this is where we start to get into the sort of mystery.
KWONG: OK.
HERSHER: So climate scientists did expect that the oceans would heat up dramatically because the vast majority of the excess heat that's trapped in the atmosphere by fossil fuel pollution is absorbed by the oceans.
KWONG: Right.
HERSHER: But the ocean temperatures for the last year or so have been even hotter than scientists expected.
SCHMIDT: The warming that we've been seeing in the North Atlantic over the last year has made people kind of lift their eyebrows a little bit and go, huh. What's going on there?
KWONG: Oh, so this is a true mystery for them...
HERSHER: (Laughter).
KWONG: ...These warming oceans. What are some of the theories?
HERSHER: There are a bunch.
SCHMIDT: Well, it could be the Saharan dust or it could be the pollutants from marine shipping. It could be the solar cycle. It could just be noise. It could - maybe the data isn't right.
KWONG: This is a wide, wide-ranging list.
HERSHER: Yes. Also, that is not the whole list. He kept going. So basically, you can group the theories into some buckets. So either there's something going on with the sun that we don't totally understand...
KWONG: Great.
HERSHER: ...Or the amount of dust and air pollution in the air is changing how much heat gets trapped. Or maybe this is a math problem - right? - where there's some error in the computer models and the data that feeds them. But there's one other big theory that doesn't fit into any of those buckets, and it's about a volcanic eruption.
KWONG: I thought volcanic eruptions kind of cool the atmosphere. Like, the ash shoots up into the air, temporarily reflects extra heat from the sun.
HERSHER: Yes, usually. That is also my understanding of volcanic eruptions. This is...
KWONG: Yeah.
HERSHER: ...Why this is such an interesting theory. It's about the volcano that erupted underwater near Tonga a couple years ago.
KWONG: Oh, yeah. That was big.
SCHMIDT: The Hunga Tonga-Hunga Ha'apai volcano also put a lot of water vapor into the stratosphere. We've never seen that before, and that went up really high. And water vapor in the stratosphere is actually an additional greenhouse gas.
HERSHER: So water vapor in the atmosphere, it traps heat instead of reflecting it. So it makes warming worse in the short term. And that's the idea behind that theory for why the oceans are so darn hot right now. That's one possibility, right?
KWONG: Fascinating. OK.
HERSHER: Yeah.
KWONG: But we don't know which of these theories - volcanoes, dust, data among them - is right, right?
HERSHER: No. It's a totally open question. Lots of scientists are working on it, and it's likely that it's a mix of multiple reasons.
KWONG: Sure.
HERSHER: It doesn't have to be one theory.
KWONG: Yeah.
HERSHER: In the meantime, what we do know is that human-caused climate change accounts for most of the warming in the ocean. It's - like, that part is not up for debate. And we also know that the part of the Atlantic where hurricanes form is extremely warm compared to normal, which is bad news for hurricanes.
KWONG: But is the warm ocean water the only reason for the large number of hurricanes? 'Cause honestly, it sounds like the ocean has been abnormally hot for more than a year. But last year wasn't some kind of record-breaking year for hurricanes, was it?
HERSHER: No, it wasn't. That's a great point. Last year was an average year for hurricanes. And that's because warm water isn't the only factor in hurricane formation. Wind also matters a lot, right? Storms are wind - windy systems. So last year, there weren't favorable wind conditions. There was a lot of what's called wind shear, which is when the wind speed and direction change really dramatically, which is - it can tear apart storms as they're forming. This year, wind conditions are much more favorable for hurricanes.
KWONG: Oh.
HERSHER: So this is why I say it's a bit of a perfect storm - right? - with the temperature and the wind.
KWONG: Got it. OK. This is not a good situation obviously if you live in a place that gets hurricanes, which, like you said, is just a big swath of the U.S.
HERSHER: Yeah, like, everyone from Texas to Maine, including the Inland South and Appalachia. Some of the most damaging storms in recent years have destroyed buildings and killed people hundreds or even thousands of miles from where they initially made landfall. So this is the No. 1 message that forecasters are trying to hammer home while it's still early in the hurricane season - get prepared now. Do not wait until one of these many, many predicted storms is headed your way.
KWONG: This is my favorite part of your annual hurricane updates.
HERSHER: (Laughter).
KWONG: It's so like, OK, here's what you can do about it. Here's the one thing within your control.
HERSHER: You don't need to be a sitting duck.
KWONG: No, you don't. So, like, what does being prepared mean? What are some specific things people can do?
HERSHER: So the first thing is figure out an evacuation plan, right? Like, if authorities said, you need to evacuate, where would you go? Do you have pets? Make a plan for them. What do you need to protect your home while you're away? You know, what would you pack in a bag? What is your mode of transportation?
Then also make a plan for staying at home because for some types of storms, the local guidance might be to shelter in place, to not leave. A good hurricane plan is specific to your needs. Erik Hooks, the deputy administrator of the Federal Emergency Management Agency, put it this way.
ERIK HOOKS: Do you have medication that requires refrigeration? Do you have a medical device that requires electricity? Do you have mobility challenges that make evacuations harder?
HERSHER: Right? - these are specific questions that you should be asking yourself. Basically, make a plan that fits your life.
KWONG: Yeah.
HERSHER: And then also talk to family members and neighbors who might have trouble making a plan on their own.
KWONG: And do it before the hurricane season really starts heating up, so to speak.
HERSHER: So to speak. Yes, exactly. Now is the time.
KWONG: Rebecca Hersher, thank you for this.
HERSHER: Thanks so much. You're welcome.
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KWONG: Before we head out, a quick shoutout to our SHORT WAVE Plus listeners. We appreciate you, and we thank you for being a subscriber. SHORT WAVE Plus helps support our show. And if you're a regular listener, we'd love for you to join so you can enjoy the show without sponsor interruptions. Find out more at plus.npr.org/shortwave.
Today's episode was produced by Rachel Carlson. It was edited by our showrunner Rebecca Ramirez and fact-checked by Rebecca Hersher. The audio engineer was Kwesi Lee. Beth Donovan is our senior director, and Collin Campbell is our senior vice president of podcasting strategy. I'm Emily Kwong. Thanks for listening to SHORT WAVE, the science podcast from NPR.
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