Short Wave - Why The Tropics Have A Weather Forecasting Problem

Episode Date: October 10, 2025

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 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 [e-mail] 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.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

Hey, shortwaver's 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. Anhal Adamas Corliza grew up in San Sebastian on the northwest side of Puerto Rico. So from childhood, he was used to windy weather, thunderstorms, heavy rain. But nothing really prepared him for Hurricane George in 1998. So in Puerto Rico, we cannot evacuate from hurricanes because we're on 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 like wooden panels to protect the windows and the doors. And I remember like the wind just hitting those doors. And that really left an impression on me. That hurricane really etched into his memory. I was 10. So I was a child. I couldn't believe that something so powerful and destructive was in nature's arsenal. And this memory became a driving force for Anhell's career.

He pursued his curiosity about whether 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 Noah said was the 10th most intense Atlantic hurricane on record. Maria was a life-changing experience. 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.

With that storm, Anheel again felt nature calling him, pushing him. 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 it. any other community that's in the tropics and be able to tell people, 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. On hell 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 Anhell 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. 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... Anheel told us, it meant a lot to be chosen to get this kind of recognition and bring it back to the island. You know, coming from Puerto Rico, Puerto Rico 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 in 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 Markarfer 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. 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 on hell's work is contributing to make weather forecasts better for everyone. I'm Emily Kwong, and you're listening to Shortwave, the science podcast from NPR. All right, let's talk about the weather and atmospheric science. 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.

Yes. And in the southern hemisphere, the mid-latitude covers what, the bottom of South America, a little bit of Australia. Yeah, most of Australia, like a good chunk of Australia, New Zealand, this 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, to the research that I do. Okay. 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. Weatherness is very, very changing. Temperatures change very dramatically. It can be really, really dry. 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 has been known about tropical systems in the past? So there was a lot of

common knowledge. For example, the indigenous populations of the Caribbean knew about hurricanes. So Taino, for example, they had the semi, which is kind of like their entity of destruction is Huracan. 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 Niño. 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 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 American Europe knew nothing about the tropics until World War II. What changed in World War II and what did they figure out? So World War II came and what happened was that the U.S. and the allied countries got into war with Japan. And Japan had taken over a lot of islands in the 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 get a hurricane. But then people started realizing, oh, oh, dang, weather in the tropics does actually

change at a substantial scale. And this is all summarized in the first Tropical Meteorology book ever written by somebody in the Northern Latest, by Herbert Reel in the 1950. 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 II. 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. What do we know so far?

How is it different? It's super different. So the first thing that's like, there are some really guiding principles for the mid-latitude dynamics that we teach in the classroom. For example, we have this thing, this very important balance that's called geostrophic balance. So it's actually, so if you look at the major weather patterns, you have the jet stream, right? The jet stream, that is that big current of wind that moves from west to east over the Atlantic? Yeah, yeah.

So commercial aircraft take advantage of the jet stream, and then they fly along the jet stream to make the flight faster, but then they have to fly against it on the way back, so it's actually slower. Right. So we know that these currents exist, and they're actually in a very, very, very elegant balance. The winds want to accelerate to the poles, but then the coriolis force, which is the bending effect that you get from the planet being in rotation, it bends it the other way.

So it causes all, the combination of these forces creates the jet stream, and the gesturing goes 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 pattern. 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 you just get days that are warm and then days that are cold in alternation. Oh, so that explains the mid-latitude variability. Right, right. But the tropics is not like this? 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 alternating with dry periods. So instead of thinking about

temperature variability, it gets really cold or it gets really hot. And the tropics, it actually gets really humid or it's really dry. That's really kind of the big thing that drives weather patterns. So you're saying in the tropics, it's all about the moisture. 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 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. In light of the fact that the tropics are so different from the mid-latitudes, what's surprising to me, and I, I, you said this elsewhere in some of your work,

is that there's no, 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? So I don't think we still have a comprehensive theory of the tropics. At least when you compare it to the mid-latuces, where we, 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 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 mid latitudes. 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 focus on was something called the Madden Julian Oscillation, or M.J.O. Yep. Which is this large region of thunderstorm activity.

in the tropics. Right. So the MJA 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. It's comparably as important as El Nino. Really? The M.J.O. Yeah. Okay. And it has not just massive impacts in the tropics, but it has impacts throughout the globe. It actually modulates weather in the midlides. For example, at Missouri, for example, atmospheric rivers that cause flooding in California are modulated by the MJAO. So it's a global phenomenon. It's rooted in the tropics. It starts in the deserts. It starts in the deserts. 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, hurricane activity increases, and so forth. So you started studying the MJO. What did you find? And what does the MJO tell us about the tropics as a whole? 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 MGO 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 changed 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 free things get coupled together. The moisture, the rains, and the winds, they couple together. They're playing off each other. Yeah, they play off each other. So they feed back on each other. And so that causes the MGO to move. 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 work the same way?

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? 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 forecasts. Everybody deserves to know to the best degree possible what's going to happen in the climate and 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. Anheel, thank you so much for coming on to Roeven. Congratulations again. Thank you. On your grant. Thank you so much.

This episode was produced by Hanna 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 Shortwave from NPR.