What's On The Horizon For Hurricane Season?

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Peak hurricane season typically lasts from August to October. Gerry Bell, lead seasonal hurricane forecaster for the National Oceanic and Atmospheric Administration, explains the climate patterns and ocean temperatures that lead to hurricanes, and offers advice on how to prepare for storms before they hit.


This is SCIENCE FRIDAY from NPR News. I'm Ira Flatow.

Hurricane Bill is churning up in the Atlantic, heading north towards Canada and getting by Bermuda about this point. What else can we expect this year and why? Here to talk about it today is NOAA's lead hurricane forecaster Gerry Bell. He is the, as I say, the seasonal hurricane forecaster, the lead for NOAA, the National Weather Service. He joins us from the Climate Prediction Center in Maryland. Hi, welcome to SCIENCE FRIDAY.

Dr. GERRY BELL (National Oceanic and Atmospheric Administration): Good afternoon, Ira. It's a pleasure to be here.

FLATOW: Nice to have you back. What is Bill up to?

Dr. BELL: Well, Bill is now weakening a little bit. It's a Category 2 storm, but don't let that be deceptive. It's still a very powerful, very big hurricane. And as Bill moves northward, it's expected to produce very high surf, anywhere from eight to 14 feet, with the higher levels being Saturday and Sunday along a lot of the East Coast.

That, along with - that is expected to then produce very strong rip currents and deadly rip currents. So people should be not - even though it's hot and muggy along the East Coast here, after this afternoon, be very careful about getting in the water. And certainly do not go in any beaches that are unsupervised or by yourself because strong rip currents can kill you.

FLATOW: It seems Bill's out there by Bermuda, way out in the Atlantic. Is that an unusual place to find a hurricane?

Dr. BELL: Most hurricanes have a track where they head up north of the Bahamas and then eventually curve to the north and then northeast. So no, Bill is taking a typical track for a hurricane.

FLATOW: And it could hit Canada. Is that correct?

Dr. BELL: That's possible, yes, northeastern Canada, it could - it's still possible it could hit Canada as a hurricane. But our immediate concern is even though, as I mentioned, even though Bill is well out to sea, there - anybody with maritime interest should be watching Bill, and also just for regular people, be very careful about going in the beach waters this weekend, if at all.

FLATOW: Yeah, because a lot of those Saturday surfers up here in the Northeast, going to say, wow, big waves, I'm going to get out there. And it's not a good thing to do. Let's talk about why does El Nino mean less tropical storms this year?

Dr. BELL: Well, El Nino is a climate phenomenon that refers to a warming of the ocean waters in the tropical Pacific Ocean along the Equator. And you might - you say, well, how can something in the Pacific affect the Atlantic? Well, the warm waters from El Nino affect the wind patterns in the atmosphere far, far distant from the Pacific. And what they do is they act to increase the wind shear over the Atlantic Ocean, and that suppresses the Atlantic hurricane activity.

FLATOW: So it sort of lops off the top of the hurricane?

Dr. BELL: That's right. Wind shear refers to how the wind speed and direction change as you go up through the atmosphere. If there's a strong change in wind speed and direction, which is what El Nino produces, that's called strong wind shear, that either will not allow hurricanes to form or if they do form can just rip them apart.

FLATOW: Yeah, so we're not expecting as many major hurricanes this year.

Dr. BELL: That's right. NOAA's latest seasonal outlook that we issued on August 6th is calling for one to two major hurricanes. We've already got one with major Hurricane Bill. We're, for the season, expecting three to six hurricanes and seven to 11 named storms.

FLATOW: How do make a prediction like that? What goes into your equation?

Dr. BELL: Well, it turns out that there's a couple of dominant climate factors that strongly control the wind and air pressure patterns over the Atlantic and therefore strongly control the overall strength of the hurricane season. One of those patterns is the tropical climate patterns that can last anywhere from 25 to 40 years at a time and are responsible for active hurricane eras, such as we've been in since 1995 and also lower-activity eras.

Another major climate factor is El Nino and its counterpart, La Nina, which affect the hurricane season strength from one year to the next. And also we look at the Atlantic Ocean temperatures. And by analyzing and predicting and understanding the net effects of these three dominant climate factors, we can often estimate the strength of the hurricane season.

FLATOW: Can you tell us anything about individual storms? Does your prediction say that if we have a storm, it will be stronger or weaker this year?

Dr. BELL: Well, it does in terms of the predictions for how many systems might become hurricanes and how many might become major hurricanes, but it does not - a seasonal forecast doesn't say anything about a specific event.

I think it's also important to point out that these outlooks really are a statement of the overall strength of the hurricane season. They're not a prediction of how many storms might strike the United States, nor are they any indication of whether a particular locality might be affected. So regardless of the seasonal hurricane outlook, coastal residents should prepare each and every season for the hurricane season.

FLATOW: A question coming on Tweet, coming in from SM Beaverson(ph), who wants to know, what is the largest recorded hurricane?

Dr. BELL: The largest recorded hurricane in the Atlantic, they typically reach about 165 miles per hour. They're very powerful, major hurricanes. The strongest hurricanes on the planet we tend to see in the Western Pacific. Some of those strike China or Southeast Asia, and some of those storms can reach 180, 190 mile-an-hour winds.

FLATOW: So Katrina was not the strongest hurricane on record?

Dr. BELL: That's correct. But that brings up a good point that the hurricane strength is only one factor that determines the damage. Hurricanes cause damage from storm surge, winds, tornadoes, flooding, and in Katrina's case, destruction of the levees that led to subsequent flooding.

So it's not just the strength of the hurricane that matters, and that's why I mention that although Bill is now Category 2, we're going to see the same impacts on the winds, whether it's technically a Category 2 or 3 doesn't matter.

FLATOW: How did they prepare in advance for a hurricane coming way before we had satellite pictures and things like that to let us know?

Dr. BELL: We didn't. Typically before satellites and aircraft measurements back in the mid- to late 1940s, people generally didn't know a hurricane was coming until it struck. And then you had these tremendous death tolls, Galveston, Texas, in the early 1900s and so on.

Now with satellites and predictions and these seasonal forecasts, we can warn people, you know, and encourage people. Have a preparedness plan in place. Think about how a hurricane might affect you, be it the storm surge or tornado or flooding. And then think about ways you can mitigate those impacts.

We are now in the peak of the hurricane season. Coastal residents, you should already have your hurricane preparedness plan done. If you need to complete it, do so. Once a hurricane's approaching, it's too late to start thinking about what to do. You should already know what to do ahead of time because we see time and time again that if you do have a plan and a hurricane threatens, you will be much better prepared than those that have not.

FLATOW: Gerry, as a hurricane scientist, I'm going to give you my blank-check question. If you had a blank check and you could buy any piece of equipment or create a technology that would help you better to do your work in the hurricane business, what would you like? What do you need? What kind of technology would you like to have that you don't have?

Dr. BELL: Well, that's hard to say because we have tremendous technologies that are currently brought to bear on the hurricane problem. We have global monitoring efforts. We can see the global weather patterns daily. We have excellent satellite capabilities to see these hurricanes. There's new satellite technologies being developed to even better estimate the winds, and so on.

But one of the best things we can do, and NOAA is heavily involved with this, is developing even better global observing systems because with those improved systems, we can run better climate models and make even better seasonal predictions. And one place we'd like to go with this is to make - eventually be able to make seasonal hurricane landfall forecasts. That capability just does not exist right now, but it would be - that's something I look forward to in the future.

FLATOW: You mean to actually predict when a hurricane - where it would land exactly?

Dr. BELL: Well, more general in terms of to say, well, maybe this season we're predicting a certain strength and, by the way, we're expecting more of the hurricanes to, say, affect the Gulf Coast or more maybe to affect Florida or be able to say something about more - potential local impacts.

FLATOW: A lot of people ask all the time whether we could do anything, cloud seeding or any kind of technology to break up a hurricane or to mitigate it. Are we at that point?

Dr. BELL: My understanding is no. That's not my area of expertise, though.

FLATOW: It's a pretty strong thing, a hurricane, isn't it?

Dr. BELL: Oh, tremendous, tremendous. The smartest thing that we can do is, as a nation right now, is to understand that we are in an active hurricane era. We will continue to see high levels of hurricane activity for many years to come. And there is a threat of hurricanes striking the U.S. each and every hurricane season, regardless of its strength.

The smartest thing that people can do is to have a plan ahead of time, evacuate if they're asked to do so. Do simple things like don't go in the high surf this weekend and have your life potentially threatened. There's a lot that we can do to mitigate or reduce hurricane impacts, and we need to do them and better.

FLATOW: You know, when folks in the health care business or the flu season business want to know what the flu season may be like, they look at, you know, where it's winter now, when the flu is happening, like in the Southern Hemisphere. Can you look at tornados, hurricanes, whatever the weather is in the Southern Hemisphere and get any prediction of what might happen in our season that comes up?

Dr. BELL: No, the main predictors for the seasonal hurricane strength are, as I mentioned, the El Nino/La Nina cycle, the Atlantic Ocean temperatures and these long-period patterns that produce active and inactive eras for anywhere from 25 to 40 years at a time.

These are global climate patterns. They affect not just the Atlantic. We're interested in them for hurricane forecasts because they do affect the Atlantic, but they have global impacts, and we monitor and understand those as a matter of course.

FLATOW: What's the water temperature of the Gulf these days?

Dr. BELL: Well, the Gulf of Mexico is generally about 86 degrees Fahrenheit or so. The Gulf of Mexico reaches its peak temperatures during this time of the year.

FLATOW: Because I remember when everybody was focused on Katrina in those years of big hurricanes, we were talking over-90-degree temperatures there.

Dr. BELL: Sure. That's very warm water and as we see, when hurricanes do get in the Gulf of Mexico, they can often strengthen considerably, partly because of the very warm water and also partly because the wind shear tends to be low. And Gulf of Mexico systems are also a threat because there's nowhere to go but to make landfall.

FLATOW: All right, Gerry, thank you very much for taking time to be with us.

Dr. BELL: Thank you, Ira.

FLATOW: And we'll see if we can heed those warnings that you're giving out. Gerry Bell is the lead seasonal hurricane forecaster for NOAA, the National Weather Service, and he was joining us from the Climate Prediction Center at Camp Springs, Maryland.

We're going to take a break and switch gears and come back. We're going to talk about - we're going to talk with Sheril Kirshenbaum, who is going to be here to talk about "Unscientific America: How Scientific Illiteracy Threatens our Future." 1-800-989-8255. You can also Tweet us @scifri, @-S-C-I-F-R-I. Stay with us. We'll be right back.

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Recent Hurricanes Not Matched Since Middle Ages

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Hurricane Katrina was one of the most powerful storms to strike the United States. i

Hurricane Katrina was one of the most powerful storms to strike the United States, with winds of 160 miles per hour and stronger gusts. Medieval sediments taken from lagoons in the Atlantic suggest that 1,000 years ago there was a hurricane season similar in intensity to the 2005 season. Jeff Schmaltz/MODIS/NASA/GSFC hide caption

toggle caption Jeff Schmaltz/MODIS/NASA/GSFC
Hurricane Katrina was one of the most powerful storms to strike the United States.

Hurricane Katrina was one of the most powerful storms to strike the United States, with winds of 160 miles per hour and stronger gusts. Medieval sediments taken from lagoons in the Atlantic suggest that 1,000 years ago there was a hurricane season similar in intensity to the 2005 season.


The Atlantic Ocean is experiencing the most intense period of hurricane activity in 1,000 years, according to a study in the journal Nature.

The study looked at hurricane activity during the past 1,500 years using techniques that have emerged from a field often called paleotempestology.

The discipline relies on scientists who hunt for physical evidence of ancient storms, says Michael Mann, an author of the study and director of the Earth Systems Science Center at Pennsylvania State University. These researchers often search for evidence of ancient storms by studying lagoons that are separated from the open ocean except when a hurricane causes water to rush over the land barrier, Mann says.

"Typically they send a coring device into the bed of the lagoon," he says. "What one looks for are layers of sediment in that core that tell you that there was an event that was strong enough to take the stuff from the open ocean and bring it all the way across the barrier into that lagoon environment."

Studying these layers is a bit like using tree rings to see what the weather was like hundreds of years ago.

Paleotempestologists also search for evidence of conditions that would have favored hurricanes centuries ago. These include warm ocean temperatures in parts of the Atlantic and the presence of La Nina, an atmospheric phenomenon that creates wind conditions that help storms gain strength.

Coral growth patterns can reveal when the water was warm. Ice cores help identify La Nina years.

Medieval Era Ideal For Hurricanes

When Mann and his team reviewed that sort of evidence, they found that the conditions were ideal for hurricanes in the Middle Ages. "There appears to have been sort of a perfect storm of conditions about a thousand years ago that relate to these various influences," he says.

Perfect conditions don't necessarily produce storms, though. So Mann's team looked at medieval sediments taken from lagoons between Massachusetts and Puerto Rico.

And the sediments confirmed that a number of storms actually had struck the coast during that period.

It was probably a lot like the 2005 season, which was the busiest hurricane season in the Atlantic in recorded history. The season witnessed 28 named storms, including Katrina and Rita.

But the current period of intense hurricane activity differs from the medieval one in an important way, Mann says. Today's storms are associated primarily with warmer ocean temperatures, rather than the influence of La Nina.

"We believe a substantial part of the reason for that anomalous recent warmth is in fact the human influence on climate," Mann says.

There is still debate among scientists about the effect of warmer water on hurricanes. And skeptics say it could have been a coincidence that the medieval storms came during a period of warm water and La Nina conditions.

But the new research on ancient hurricanes is providing a kind of information that modern satellites and aircraft surveillance just can't, says James B. Elsner, a professor of geography at Florida State University.

"It does provide us some additional clues about how things might change in the long term," he says.

And this study, he says, supports the idea that global warming is one reason we're seeing so many hurricanes these days.



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