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Science & Environment

Rain, Surge And Wind: How To Understand Your Hurricane Risk

Hurricane Florence approaches the Carolinas in September 2018.
Hurricane Florence approaches the Carolinas in September 2018.

Millions of Americans live in the potential path of a hurricane.

The good news is that hurricane and cyclone forecasts have gotten significantly more accurate in recent decades. The bad news is that climate change and population growth combine to make hurricanes more dangerous to more people.

And research suggests that people are confused by common graphics and warnings about where hurricanes are headed and how they'll affect communities in their path.

Here are some basic principles you can use to avoid confusion when a hurricane is headed your way.

Storms Are Large

Figuring out whether you and your family are in the potential path of a hurricane is the first step. When a storm forms, the National Hurricane Center publishes a prediction map that shows where the hurricane is headed.

That map is often called the "cone of uncertainty." It sometimes has a central line that shows the most likely path of the hurricane. Imagine that the line starts at the current location of the storm — somewhere over the water — and extends toward the land, showing you where the storm is likely to be in the coming hours and days.

But each location along the storm's projected path is less and less certain, because it's farther in the future. The storm could move slightly left or slightly right at any moment, and that changes where it ultimately makes landfall. The map illustrates that uncertainty with a shaded blob that shows the total area where the storm's center is likely to fall.

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Water Over Wind

The "cone of uncertainty" map is usually published along with information about the storm's wind category. The categories range from tropical storms with sustained wind below 74 miles an hour up to Category 5 storms with sustained winds above 157 miles per hour.

But, although high winds can destroy buildings, water is the most deadly part of a hurricane. And a storm's category doesn't tell you anything about the flooding it will cause.

"My number one message to people is to focus less on wind and more on water," says Jamie Rhome, a senior forecaster at the National Hurricane Center. "The cone of uncertainty tells you very little about storm surge or rain, which are consistently the deadliest effects of hurricanes."

Storm surge is water pushed up onto coastal land by the hurricane. The National Hurricane Center publishes storm surge forecast maps that show which areas are in danger, and how much water could arrive with the storm.

There's also a diagram that shows how high the water will be relative to people of different heights. The message: you cannot walk or swim through a flood. Just a few inches of moving water can knock you off your feet or make it impossible to control your car.

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For people who live further inland, rain is likely to be the most destructive effect of a storm. Just because a hurricane weakens as it moves over land doesn't mean people in its path are out of harm's way. In 2017, Hurricane Harvey had weakened to a tropical storm when it arrived in Houston and dropped upwards of 60 inches of rain.

Preparing for flooding is more important than it's ever been. As the Earth gets hotter, large, wet storms are getting more likely. Meanwhile, the number of people living in hurricane-prone areas along the coast is steadily increasing, putting more people at more risk.

Where And How To Go

Unfortunately, storm surge and rain maps do not include local information about where to go and how to prepare. That's because local emergency managers are in charge of deciding when to recommend evacuations, where to set up shelters and how to manage evacuation routes.

When hurricane season begins in early summer, check with your county or city emergency department to find out whether you're in an evacuation zone, and what your options are if you decide to leave your home.

"Hurricane risks are different for different people," explains Barbara Millet, the director of the University of Miami's User Experience Lab. Millet studies risk communication and says it's currently very difficult for citizens to get all the information they need when a hurricane is headed their way.

"Information like: am I in an evacuation zone? What types of things should I be doing? Where is there a shelter? Should I be evacuating on a certain route versus another route?" explains Millet, as well as basic information about where to get gas and other supplies. "That type of information is what they're looking for, but that's not necessarily being conveyed" by the cone of uncertainty or other storm warnings.

The upshot: make a plan before a storm is headed your way, and remember that water, not wind, is the biggest danger you're likely to face during a hurricane.

Copyright 2020 NPR. To see more, visit https://www.npr.org.