Know about the hurricanes, its formation, and the challenges in forecasting
Know about the hurricanes, its formation, and the challenges in forecasting
Learn how hurricanes form in this interview with John P. Rafferty, earth and life sciences editor at Encyclopædia Britannica.
Encyclopædia Britannica, Inc.
Transcript
SPEAKER 1: So, John, thanks for joining us again. I know that we spoke about severe weather pretty recently. But now, we're in the heart of hurricane season.
So I thought it would be great to have a conversation specifically about hurricanes. To start, can you go over again how a hurricane forms?
SPEAKER 2: Well, a hurricane forms much the same way as a thunderstorm forms. You need a heat source and you need moisture. And that's what really gets things started.
In this case, in the case of a hurricane, it's warm ocean water. And that is the fuel source. Not only for the heat, but also for the moisture that kicks off the hurricane.
OK. So what you're going to get is during the middle of the day, you're going to get evaporation off that warm surface, that warm water. That liquid water is going to turn to water vapor. It's going to rise in the air column. And when it gets to a certain height, it's going to condense into clouds.
Well, the warmer that fuel source is, the warmer that moisture source is, the more of that activity takes place. And you get what are known as convective thunderstorm clouds.
Over the ocean, you get a lot of these in what's known as a tropical disturbance. And that becomes a tropical storm. And it grows and grows and grows and grows into a hurricane.
As long as our fuel source is there, as long as that water source is there, it can either sustain itself or get stronger.
SPEAKER 1: What's the strongest part of a hurricane?
SPEAKER 2: Well, a hurricane itself is a mix of a number of different parts. Toward the center, it's going to be more concentrated and stronger. Much in the same way, a figure skater.
Figure skater is spinning and then pulls his or her arms and arms and legs. And they increase the spin. So towards the center, it's that physical relationship that causes that.
So the eye wall, the eye wall is the strongest part of the storm. It's the area that has the highest wind speed and the greatest amount of rain. Because there's just so much activity going on in that part.
So that's when the National Weather Service, they say when landfall happens, it's when the eye wall. When the eye starts to pass over the shoreline, that's when landfall happens.
SPEAKER 1: When you turn on the news and there's coverage of a hurricane, they talk about the different categories of a hurricane. What determines a category of a hurricane?
SPEAKER 2: There are five different categories of hurricane. And they're defined by how fast the winds are. So category one begins at 74 miles an hour goes up to 95 miles an hour.
Some of the larger hurricanes. Just incredible wind speeds category 5 storms. The wind speed for those types of phenomenon are 157 miles per hour.
Hurricane Katrina, a very famous storm that struck the Gulf Coast in 2005. There was a category 4 storm. That's 130 to 156 mile an hour winds at landfall.
So these are incredibly strong storms that are capable of ripping roofs off of structures, damaging walls. In some cases in the category 5 storms, they can actually rip a house off of its foundation leaving virtually nothing left.
SPEAKER 1: And can you talk a little bit about the other factors that make hurricanes dangerous obviously the wind? But rain can cause flooding. And there's also a term called storm surge. If you could talk about that a little bit that would be great.
SPEAKER 2: Sure. Well, we've talked about the winds, so the winds are a very important feature of a hurricane. But also the rain. With these very intense thunderstorms, very super intense thunderstorms, you're going to get a lot of rain. And that's going to produce flash floods and contribute to flooding overall.
But probably, one of the most dangerous parts of a hurricane is what's known as the storm surge. And the storm surge is the water that comes ashore pushed by the winds of the hurricane itself.
So remember, when we were talking about how hurricanes form, we noted that there they form over a region of warm water. So as a result, you're going to get that dome of sea surface water that's actually going to expand. So the water will actually be deeper or actually rise up a little bit.
So you've got this bubble of warm water. That's a little bit higher than normal sea conditions. And it's being pushed by the wind inland.
So you're going to get more intense flash flooding, you're going to get more intense flooding overall just because you've got that volume of water moving inland that much further. And that's why forecasting is so important. And the better the Meteorological Organization is good at forecasting, the better able they are to predict where that high damaged area is going to be so then I can help to target evacuations more effectively and prepare the people who do stay on to weather the storm.
SPEAKER 1: How come forecasting the track of a hurricane is so difficult?
SPEAKER 2: OK. Well, the track itself is dependent on the prevailing winds. So the hurricane is an atmospheric phenomenon. And it gets pushed around by the prevailing winds, the westerly is here in North America as much as any other storm coming across the plains to get the Midwest.
So it's going to be governed by those winds the jet stream, those kinds of things. But it's also important to track the storm in terms of its intensity because the storm could travel over a warm part of the ocean at one phase. But then in a second phase, pass over a cooler part. So then it's not receiving quite as much fuel.
So it can both rise and fall in intensity, but also that can help work with the atmospheric forces to alter the path a little bit.
SPEAKER 1: And there is a hurricane season. Can you talk a little bit about why there's a specific amount of months that hurricanes are more frequent?
SPEAKER 2: Well, this has to do with the heating. The uneven heating that the earth experiences in a given year. Again, with hurricanes and tropical storms, they're going to be more intense and they're going to appear
during those times of the year, where you have a warm pool of water. So the hurricane season lasts between June 1st and November 30th here in the North Atlantic. Then why so deep into the year? It's because that heat that we built up in the early part of the year can be dispersed around, and there is still some potential that even as late as November, there are certain parts of the ocean that could be warm enough to help contribute to hurricane development.
SPEAKER 1: Well, John thanks again for joining us. Hopefully the rest of this season isn't too intense.
So I thought it would be great to have a conversation specifically about hurricanes. To start, can you go over again how a hurricane forms?
SPEAKER 2: Well, a hurricane forms much the same way as a thunderstorm forms. You need a heat source and you need moisture. And that's what really gets things started.
In this case, in the case of a hurricane, it's warm ocean water. And that is the fuel source. Not only for the heat, but also for the moisture that kicks off the hurricane.
OK. So what you're going to get is during the middle of the day, you're going to get evaporation off that warm surface, that warm water. That liquid water is going to turn to water vapor. It's going to rise in the air column. And when it gets to a certain height, it's going to condense into clouds.
Well, the warmer that fuel source is, the warmer that moisture source is, the more of that activity takes place. And you get what are known as convective thunderstorm clouds.
Over the ocean, you get a lot of these in what's known as a tropical disturbance. And that becomes a tropical storm. And it grows and grows and grows and grows into a hurricane.
As long as our fuel source is there, as long as that water source is there, it can either sustain itself or get stronger.
SPEAKER 1: What's the strongest part of a hurricane?
SPEAKER 2: Well, a hurricane itself is a mix of a number of different parts. Toward the center, it's going to be more concentrated and stronger. Much in the same way, a figure skater.
Figure skater is spinning and then pulls his or her arms and arms and legs. And they increase the spin. So towards the center, it's that physical relationship that causes that.
So the eye wall, the eye wall is the strongest part of the storm. It's the area that has the highest wind speed and the greatest amount of rain. Because there's just so much activity going on in that part.
So that's when the National Weather Service, they say when landfall happens, it's when the eye wall. When the eye starts to pass over the shoreline, that's when landfall happens.
SPEAKER 1: When you turn on the news and there's coverage of a hurricane, they talk about the different categories of a hurricane. What determines a category of a hurricane?
SPEAKER 2: There are five different categories of hurricane. And they're defined by how fast the winds are. So category one begins at 74 miles an hour goes up to 95 miles an hour.
Some of the larger hurricanes. Just incredible wind speeds category 5 storms. The wind speed for those types of phenomenon are 157 miles per hour.
Hurricane Katrina, a very famous storm that struck the Gulf Coast in 2005. There was a category 4 storm. That's 130 to 156 mile an hour winds at landfall.
So these are incredibly strong storms that are capable of ripping roofs off of structures, damaging walls. In some cases in the category 5 storms, they can actually rip a house off of its foundation leaving virtually nothing left.
SPEAKER 1: And can you talk a little bit about the other factors that make hurricanes dangerous obviously the wind? But rain can cause flooding. And there's also a term called storm surge. If you could talk about that a little bit that would be great.
SPEAKER 2: Sure. Well, we've talked about the winds, so the winds are a very important feature of a hurricane. But also the rain. With these very intense thunderstorms, very super intense thunderstorms, you're going to get a lot of rain. And that's going to produce flash floods and contribute to flooding overall.
But probably, one of the most dangerous parts of a hurricane is what's known as the storm surge. And the storm surge is the water that comes ashore pushed by the winds of the hurricane itself.
So remember, when we were talking about how hurricanes form, we noted that there they form over a region of warm water. So as a result, you're going to get that dome of sea surface water that's actually going to expand. So the water will actually be deeper or actually rise up a little bit.
So you've got this bubble of warm water. That's a little bit higher than normal sea conditions. And it's being pushed by the wind inland.
So you're going to get more intense flash flooding, you're going to get more intense flooding overall just because you've got that volume of water moving inland that much further. And that's why forecasting is so important. And the better the Meteorological Organization is good at forecasting, the better able they are to predict where that high damaged area is going to be so then I can help to target evacuations more effectively and prepare the people who do stay on to weather the storm.
SPEAKER 1: How come forecasting the track of a hurricane is so difficult?
SPEAKER 2: OK. Well, the track itself is dependent on the prevailing winds. So the hurricane is an atmospheric phenomenon. And it gets pushed around by the prevailing winds, the westerly is here in North America as much as any other storm coming across the plains to get the Midwest.
So it's going to be governed by those winds the jet stream, those kinds of things. But it's also important to track the storm in terms of its intensity because the storm could travel over a warm part of the ocean at one phase. But then in a second phase, pass over a cooler part. So then it's not receiving quite as much fuel.
So it can both rise and fall in intensity, but also that can help work with the atmospheric forces to alter the path a little bit.
SPEAKER 1: And there is a hurricane season. Can you talk a little bit about why there's a specific amount of months that hurricanes are more frequent?
SPEAKER 2: Well, this has to do with the heating. The uneven heating that the earth experiences in a given year. Again, with hurricanes and tropical storms, they're going to be more intense and they're going to appear
during those times of the year, where you have a warm pool of water. So the hurricane season lasts between June 1st and November 30th here in the North Atlantic. Then why so deep into the year? It's because that heat that we built up in the early part of the year can be dispersed around, and there is still some potential that even as late as November, there are certain parts of the ocean that could be warm enough to help contribute to hurricane development.
SPEAKER 1: Well, John thanks again for joining us. Hopefully the rest of this season isn't too intense.