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Why The Way Hurricanes Are Classified Can Be Deceptive


President Trump will visit North Carolina tomorrow to see areas that were affected by Florence. Even though the storm came ashore as a Category 1 hurricane, it has dumped record-setting amounts of rain on the Carolinas. Hurricane categories only consider wind speeds, not rain, so a storm like Florence raises the question of whether the traditional way of categorizing storms makes people dangerously complacent. Meteorologist Bryan Norcross is a hurricane specialist at The Weather Channel and WPLG TV in Miami. Welcome to ALL THINGS CONSIDERED.


SHAPIRO: Why does the category of a hurricane consider only wind speed and not water?

NORCROSS: Because we can measure the wind speed very reasonably well, and we can measure the pressure of the storm. But what we don't know is how the rainfall or the storm surge, which is the ocean being pushed up over the land, is going to interact with the particular land area that the hurricane is going to hit. For example, Hurricane Florence would have had a significantly different effect on Florida than it did in North Carolina because the coastline is different, the terrain is different. So it's just impossible, really, to put a number on the storm that will tell us how bad it will be when it interacts with the land because the land is such a big player in that.

SHAPIRO: Do you think that in North Carolina there were people who wound up in harm's way because they said to themselves it's only Category 1 even though at the same time everyone was saying this is going to be a rain event, not a wind event, there will be flooding, get out?

NORCROSS: I think absolutely that happened. People that waited saw the storm - the wind speeds lower in the storm and they stayed. But what's happened is as more and more meteorological information has come out over the years, people pay more attention to the meteorological information and less attention to whether evacuations have been ordered for specific areas. And I'm talking about in places that are generally populated. And the most important safety information is, am I ordered to be evacuated or not? And that information is so often these days muddied by spaghetti plots and cones and models and projections of wind speeds and all those things when what we know is that even Category 1 hurricanes can be disastrous.

SHAPIRO: Well, do you think there is some more holistic, nuanced way of categorizing hurricanes even if you can't exactly measure how much rain or how much storm surge there will be, something that factors in more than just the wind speed?

NORCROSS: I would do it in two ways. One is I would just start saying wind Category 1, wind Category 4, just as a way to label the hurricane to get people used to the idea of the word wind associated with category. The other thing that I think could be done is - in the case of Florence, most conversations were about what a terrible flood this was going to be. But there really is nothing but a flood watch that goes up. And flood watches go up all the time. And I think we need a different category of pre-alert that this is an extreme flood threat, or something like that, that they draw so that whenever the hurricane is discussed when it's three or four days out, it's discussed as being wind Category 3 storm, extreme flood threat is issued for North and South Carolina way in advance, not waiting for the 48-hour window and waiting for it to start raining.

SHAPIRO: We know that climate change is going to make this more relevant for more storms going forward. Do you think there's any real chance of changing the way these are described to give people a little more of a heads up?

NORCROSS: Well, the National Hurricane Center is working really hard to think about the next generation of how storms are alerted. And they're doing a lot of work, including social science research and getting ideas from a lot of people on how they can move forward to make it better.

SHAPIRO: Bryan Norcross is a hurricane specialist with The Weather Channel and WPLG TV in Miami. Good to talk to you again. Thanks a lot.

NORCROSS: Thanks, Ari. Transcript provided by NPR, Copyright NPR.