Why The Tropics Have A Weather Forecasting Problem

Weather in the tropics is decidedly different than it is in the middle latitudes. It turns out, so are the weather systems – the factors that create things like the daily temperature and humidity! Historically, most weather forecasting models have been based on data from high-income countries in the northern hemisphere. But different factors drive weather and climate near the equator – meaning that these weather forecast models are much less accurate at predicting weather in the tropics. This has implications for storm readiness, flooding preparedness and more. Atmospheric scientist Ángel F. Adames-Corraliza https://www.macfound.org/videos/2025-macarthur-fellow-adames-corraliza is aiming to change that. His research focuses on how water vapor – humidity – plays a key role in tropical weather systems. It’s earned him a spot as one of this year’s Macarthur Fellows. Interested in more science about how weather happens? Email us your question at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://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 https://www.npr.org/about-npr/179878450/privacy-policy

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Speaker 00

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• 0:16Emily Kwong?

  Hey, Shortwavers. Emily Kwong here. School has been back in session for a while now, but grades are due for Shortwave. What would you give us? An A? A B? A C? We want to know. Leave us a rating or a review on Apple Podcasts, on Spotify, on whatever platform you use to listen, and we will take your feedback seriously. I don't know if you've noticed, but we kind of like to learn. Speaking of, let's get on with it. Here's the episode. You're listening to Shortwave from NPR. Angel Adama's Corleesa grew up in San Sebastian, on the northwest side of Puerto Rico. So from childhood, he was used to windy weather, thunderstorms, heavy rain.

• 0:58Emily Kwong?

  But nothing really prepared him for Hurricane George in 1998.

• 1:03Speaker 02

  So in Puerto Rico, we cannot evacuate from hurricanes because we're in an island. So we had to kind of weather the hurricane. So we were up all night, and I just remember the winds roaring and the house shaking. My family had to put these wooden panels to protect the windows and the doors. And I remember the wind just hitting those doors, and that really left an impression on me.

• 1:26Emily Kwong?

  That hurricane really etched into his memory.

• 1:29Speaker 02

  I was 10, so I was a child. I couldn't believe that something so powerful and destructive was in nature's arsenal.

• 1:39Emily Kwong?

  And this memory became a driving force for Angel's career. He pursued his curiosity about weather all the way to a PhD in atmospheric science and meteorology. He graduated in 2016, and the following year, in 2017, another storm hit, one that changed Puerto Rico forever and that NOAA said was the 10th most intense Atlantic hurricane on record.

• 2:00Speaker 02

  Maria was.

• 2:03Speaker 02

  A life-changing experience. Like, I was not able to contact my family for weeks. It was kind of like a grieving moment. Like, nobody in my immediate family passed away from Maria, but it almost, it was like something died.

• 2:14Emily Kwong?

  With that storm, Anhel again felt nature calling him, pushing him.

• 2:19Speaker 02

  I was already like a dedicated tropical meteorologist, trying to understand how humidity, circulation, and rain interacted with one another. But I felt like this bigger desire to really want to understand what are the big driving forces? What is it that causes tropical weather to tick? And so I felt this drive to serve my community even more. Like, I wanted to be able to go back to Puerto Rico or go to any other community that's in the tropics and be able to tell people, it's like, these are the things that matter. These are the things that drive weather and climate in the tropics. These are the things that you need to pay attention to.

• 2:55Emily Kwong?

  Anhel went on to research tropical weather systems. And he's the person who has really popularized why water vapor in the tropics, humidity, is such a key player in tropical weather and climate. His work was so notable, it caught the attention of the MacArthur Foundation. Full disclosure, the MacArthur Foundation is a financial supporter of NPR. On Wednesday, the MacArthur Foundation announced that Anhel and 21 other people at the cutting edge of their different disciplines have been chosen as recipients of the MacArthur Fellowship, unofficially known as the Genius Grant.

• 3:27Speaker 02

  I was like, what? And then my brain just completely melted and I don't remember anything else from the call, to be honest. If you-

• 3:33Emily Kwong?

  Anhel told us it meant a lot to be chosen, to get this kind of recognition and bring it back to the island.

• 3:40Speaker 02

  You know, coming from Puerto Rico, Puerto Rico is, is a small island. We do have our contributions to society. We're kind of known for the arts and for like music, for example. But we don't often get recognition for science, especially my discipline. You know, like, as a community, we've been invisible. And to be able to receive this award where somebody comes out to you, in this case, the MacArthur Foundation, and they tell me like, no, we see you, you know, and we see what you're doing and we think that what you do matters. It's not just what you're doing, but what your community is doing. To me, this is everything.

• 4:14Emily Kwong?

  So today on the show, prize-worthy knowledge of tropical weather, why the tropics are so different from weather at the poles or the mid latitudes of the globe, and how Anhil's work is contributing to make weather forecasts better for everyone. I'm Emily Kwong, and you're listening to Short Wave, the science podcast from NPR.

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• 5:59Emily Kwong?

  All right, let's talk about the weather and atmospheric science.

• 6:02Speaker 02

  Mm hmm.

• 6:02Emily Kwong?

  I know early research into atmospheric dynamics began in the 20th century, and it mostly focused on countries in the mid-latitudes, between the tropics and the poles. In the northern hemisphere, the mid-latitudes cover North America, Europe, a lot of Asia.

• 6:16Speaker 02

  Yes.

• 6:17Emily Kwong?

  And in the southern hemisphere, the mid-latitude covers, what? The bottom of South America, a little bit of Australia.

• 6:23Speaker 02

  Yeah, it's most of Australia, like a good chunk of Australia, New Zealand, the very southern part of Africa, and kind of like the southern half of South America, and almost the entirety of like first world countries in the northern hemisphere, which is something that is relevant to the research that I do.

• 6:42Emily Kwong?

  Okay.

• 6:42Speaker 02

  The majority of the developed countries, they're used to the stuff that I see here in Madison, Wisconsin, which is like it gets really cold some days, some days it gets really warm. Weather is very, very shady, and temperatures change very dramatically. It can be really, really, really dry.

• 6:54Emily Kwong?

  Got it, yeah. So it sounds like the majority of weather research historically has happened in mid-latitude countries, these wealthier countries, and there's been an absence in understanding about tropical weather. What do we know? What has been known about tropical systems in the past?

• 7:10Speaker 02

  So there was a lot of common knowledge. For example, the indigenous populations of the Caribbean knew about hurricanes. So the Taíno, for example, they had the semi, which is kind of like their entity of destruction is huracán. That's where the hurricane name comes from. And so there was knowledge of these things, right? And then same with the Peruvian natives, they knew about El Nino. So local communities did know about the major phenomenon. Maybe not necessarily what drove them, but they knew about their existence. But of course, the mid-latitude countries that were actually pushing the research, they didn't really know much, right? And so there was knowledge in India, China, and other communities as well, but there wasn't that much conversation. So it's actually, I don't think it's incorrect to say that people in North America and Europe knew nothing about the tropics until World War II.

• 7:54Emily Kwong?

  What changed in World War II, and what did they figure out?

• 7:56Speaker 02

  So World War II came, and what happened was that the US and the allied countries got into war with Japan. And Japan had taken over a lot of islands independently. Pacific. So a lot of the war actually happened in the tropical Pacific. And early combat was actually kind of catastrophic. Because typhoons, actually a typhoon came and sank a navy ship, for example. Before all this happened, people had just assumed that the tropics were kind of like this paradise. It was just sunny and beautiful all the time and then maybe every now and then you'd get a hurricane. But then people started realizing, oh, oh dang, um, weather in the tropics does actually change at a substantial scale. And this is all summarized in the first tropical meteorology book ever written.

• 8:39Speaker 02

  By it by by somebody in in the northern latitude by Herbert Reel in nineteen in the nineteen fifty. So his first paragraph of the book is like, oh, we didn't know that this was serious. And then we realized that it was serious in World War Two.

• 8:49Emily Kwong?

  And in some ways, I suppose you and colleagues like yourself, you are deepening that knowledge. You are figuring out what weather is in the tropics.

• 8:57Speaker 02

  Yeah.

• 8:57Emily Kwong?

  Um, what do we know so far? How is it different?

• 9:00Speaker 02

  It's super different. So the first thing that's like, there are some really guiding guiding principles for the mid latitude dynamics that we teach in the classroom. For example, we have this thing, uh, this very important balance that's called geostrophic balance. So it's actually, uh, so if you look at at the major weather patterns, you have the jet stream, right?

• 9:18Emily Kwong?

  The jet stream, that is that big current of wind that moves from west to east over the Atlantic?

• 9:23Speaker 02

  Yeah, yeah. So so so commercial aircraft take advantage of the jet stream and then they fly along the jet stream to to make the flight faster. But then they have to fly against it on the way back. So it is actually slower.

• 9:33Emily Kwong?

  Right.

• 9:33Speaker 02

  So we know that these currents exist and they're actually in a very, very elegant balance. The winds want to accelerate to the poles. But then the the Coriolis force, which is the the bending effect that you get from the planet being in rotation, it benefits it the other way. So it causes all the combination of these two forces creates the jet stream and the jet stream goes from west to east. And in this jet, you get these waves. So you get these undulations. And these undulations are the troughs and ridges that create our day to day patterns. So that's why temperature fluctuates a lot. The polar side of the jet is really cold, the equator one is warm and the jet is waving all the time. So so you just get days that are warm and then they they start cold in alternation.

• 10:12Emily Kwong?

  Oh, so that explains the mid latitude variability.

• 10:14Speaker 02

  Right, right.

• 10:15Emily Kwong?

  But the tropics is not like this?

• 10:16Speaker 02

  It is not like this at all. So the tropics are pretty warm year round. So you don't really see that temperature variability that you see here in the mid latitude. So things like cold fronts and stuff, that barely exists in the tropics. You don't really worry about that. But yet you still get these periods where it's really, really rainy and training with dry periods. So instead of thinking about temperature variability, it gets really cold or it gets really hot. In the tropics, it actually is gets really humid or it's really dry. That's really kind of the big thing that drives weather patterns.

• 10:45Emily Kwong?

  So you're saying in the tropics, it's all about the moisture?

• 10:49Speaker 02

  It is about the moisture. Yeah, yeah. There's other things that matter too, right? Because it's always more complicated than that. But if you want, if I, if I go to a classroom and I teach people, what are the things about the tropics that make the tropics different? That's going to be one of the things that I'm going to mention. Probably the thing that I'm going to mention.

• 11:02Emily Kwong?

  In light of the fact that the tropics are so different from the mid latitudes, what's surprising to me and I, you said this elsewhere in some of your work, is that there's no, for, for a few years there, there was no textbook on tropical atmospheric dynamics. There kind of wasn't like a comprehensive theory of the tropics. How did that affect weather forecasting in the tropics?

• 11:28Speaker 02

  So I don't think we still have a comprehensive theory of the tropics. At least when you compare it to the mid latitudes where we have multiple textbooks, we have mature theory. The vast majority of weather forecasting models were initially built to tackle mid latitude weather, not tropical weather. And as a result, forecasting weather and climate events in the tropics is more daunting to the detriment of the people that live there, right? Because sometimes you do get extreme events like floods, heat waste and things that actually are very costly, not just in infrastructure, but in life. And they're not very well predicted, you know? And so that's the, the big thing, right? Like ultimately, it is. A problem of human safety and well being that we cannot forecast things in the tropics as well as we do in the latitudes.

• 12:12Emily Kwong?

  Got it. Okay. Well, in pursuit of a comprehensive dynamical theory of the tropics, you have studied many things. And one of the earliest things you focused on was something called the Madden Julian Oscillation.

• 12:26Speaker 02

  Yep.

• 12:27Emily Kwong?

  Or MJO.

• 12:28Speaker 02

  Yep.

• 12:29Emily Kwong?

  Which is this large region of thunderstorm activity in the tropics.

• 12:34Speaker 02

  Right. So, so the MJO is actually the most important tropical phenomenon that you don't know, that people don't know about. That's the way that I would like to people to think about is comparably as important as El Niño.

• 12:46Emily Kwong?

  Really? The MJO?

• 12:47Speaker 02

  Yeah.

• 12:48Emily Kwong?

  Okay.

• 12:48Speaker 02

  And it has not just massive impacts in the tropics, but it has impacts throughout the globe. It actually modulates weather in the mid latitudes. For example, atmospheric rivers that caused flooding in California are modulated by the MJO. So it is a global phenomenon. It's rooted in the tropics. It starts in the Indian Ocean. It is about the size of Russia. So it's huge. And it propagates eastward pretty slowly. And in that movement, it modulates hurricane activity. So when the MJO is active, hurricanes activity increases and so forth.

• 13:17Emily Kwong?

  Fascinating. Yeah. So you started studying the MJO. What did you find? And what does the MJO tell us about the tropics as a whole?

• 13:24Speaker 02

  When I started studying it, I started kind of learning about the importance of water vapor in tropical rainfall. And then after that, I started realizing how all these insights about the MJO translate to all sorts of other tropical phenomenon. For example, when it's humid, it starts to rain, but then all that rain actually changes the wind patterns. And the wind patterns then change in such a way that the movement, that moisture gets moved around. And so the moisture gets moved around, and so the rain moves with the moisture. So all these three things get coupled together. The moisture, the way it rains and the winds, they couple together.

• 13:57Emily Kwong?

  They're playing off each other.

• 13:58Speaker 02

  Yeah, they play off each other. So they feed back on each other. And so that causes the MJO to move, you know, or according to the theory that was being proposed at the time, which I contributed to. And so I was like, what if other tropical weather phenomenon worked the same way?

• 14:12Emily Kwong?

  Right. With the idea being that these winds move the humidity, the rain changes the wind patterns, and it becomes this recurring feedback loop of weather. Cool. Well, I have one last question for you about tropical weather. You are obviously not alone in studying it. There are a lot of other atmospheric scientists who study the tropics and who are pushing for a greater global understanding of this area, of this region. What future are you all trying to build?

• 14:39Speaker 02

  I would like to see a role in which when we're making climate reports and when we're making forecasts, that everybody is like being equally represented and that everybody's being done justice. Because at the end of the day, like, everybody deserves to have the best possible weather forecast. Everybody deserves to know to the best degree possible what's going to happen in the climate in their region right now. And right now, we don't. We don't equally have the knowledge about climate and the atmosphere for everywhere. I think that speaks volumes to where we are right now. And where we should be is a place where everybody knows the same amount about everywhere.

• 15:18Emily Kwong?

  Angel, thank you so much for coming on Short Wave. And congratulations again.

• 15:22Speaker 02

  Thank you.

• 15:22Emily Kwong?

  On your grant.

• 15:24Speaker 02

  Thank you so much.

• 15:26Emily Kwong?

  This episode was produced by Hannah Chin and edited by our showrunner, Rebecca Ramirez. It was fact-checked by Tyler Jones. Robert Rodriguez was the audio engineer. Beth Donovan is our senior director of podcasting strategy. I'm Emily Kwong. Thank you for listening to Short Wave from NPR.

• 15:47Speaker 03

  Stay tuned for the following announcements and messages from our sponsors.