(placid music) (wind howling) - 150 mile an hour winds, intense rainfall, storm surge and deadly flooding, tropical cyclones are among the most violent storms on our planet.

In the North Atlantic, we call them hurricanes, and science suggests that our warming climate is actually making these storms more intense and more destructive.

When they reached sustained winds of 39 miles per hour, we name them.

And in 2020, a record number of named storms made landfall in the U.S.

In this episode, we're gonna learn why this is happening.

And we're also gonna visit a giant lab where researchers simulate category three hurricanes so we can learn how to prepare.

(upbeat music) I'm Maiya May, I'm a meteorologist from Atlanta, Georgia, and here we know what it's like to get hit with wind and rain from tropical cyclones.

To understand why, we first need to understand how they form.

Most start as thunderstorms, which are usually blown by trade winds toward the Americas.

When they pass over warm water, warm air rises through the storm, pulling moisture high into the atmosphere, fueling and expanding the storm.

The rising air creates an area of low pressure at the ocean's surface.

Air then rushes inward in an attempt to equalize pressure, creating a feedback loop and wind.

If a storm becomes large enough, the rotation of the earth begins to spin it counterclockwise, and the center column known as the "eye" is formed.

Around the eye is the most violent part of the storm, the eyewall.

This is where the highest wind speeds occur.

When a tropical cyclone's winds reach 74 miles an hour, it is officially considered a hurricane.

Hurricanes that reach the U.S. typically leave trade winds and become influenced by westerly winds.

That includes a fast meandering air current known as a jet stream.

The jet stream often blows these storms back out towards the Atlantic, but as the climate warms, we've seen the jet stream weaken, and scientists fear this may cause more hurricanes to move slowly, and even stall.

That means the most intense part of the storm can linger and dump more rain over one area.

And that's exactly what happened when hurricane Harvey hit Texas and Louisiana in 2017.

Max Olson documents extreme weather and filmed Harvey from a hotel that was built to withstand a category five hurricane.

- We had 140 mile per hour winds whipping down the street, and there's sheet metal, (tense music) pieces of roofs, tree branches all flying down the road.

It was basically just like hell on earth.

- [Maiya] Before reaching the U.S., Harvey nearly disintegrated.

But then it turned North, over the unusually warm 86 degree water in the Gulf of Mexico.

- This storm was only a few 100 miles off the coast of Texas.

And that's when we started seeing that rapid intensification, those big thunderstorm plumes around the center.

Every refresh we're getting is even more impressive than the last, it's getting symmetrical.

And we were starting to get concerned.

It's about to get real folks, wow, look at that.

- [Maiya] Harvey continued to intensify as it headed directly towards Rockport, Texas, where Max hoped to film.

(rain splattering) - [Max] Oh yeah, yeah, that's a hurricane.

(wind howling) That's a hurricane.

(tense music) It's coming in from the roof.

- [Man] Holy, oh my God, the whole (beep) wall is gone.

(alarm ringing) - [Max] We've been in this eyewall for like... - [Man] It's been three hours.

- [Max] Yeah, it's been a super long eye wall experience.

- [Maiya] Harvey paused, pulling water in from the Gulf, and dumping 60 inches of rain over Houston, bouncing on and off the coast for an unprecedented six days.

- Generally, when you're thinking about hurricanes, you think wind is the most deadly force that's gonna be caused by the storm, but actually water, whether it be storm surge or inland flooding from heavy rains, is by far the most deadly part of the storm.

- We are still here, we still waiting.

The water is just coming, oh, I just wanna get to dry land, that's all I wanna do.

- Harvey inundated neighborhoods, and turned homes into islands.

The combination of wind and water made it the second most costly hurricane in U.S. history.

And to help us understand why there was so much water, we turned to World Resource Institute's Kelly Levin.

- There's a scientific equation where for every degree Celsius of warming, you have 7% more moisture in the atmosphere.

And that allows this deluge of water, and really record level rainfall hitting towns and cities.

- Over the last century or so, (placid music) the average global temperature has increased by just over 1.2 degrees Celsius or two degrees Fahrenheit.

And since warmer air holds more moisture, that means more rainfall during hurricanes.

And NASA recently found that hurricanes are moving 17% slower than they were just a century ago, causing them to dump even more rain.

One theory to explain why this is happening centers around the jet stream.

Again, that's a fast meandering westerly wind that usually helps turn cyclones to the East and back out to the Atlantic after a U.S. landfall.

Surprisingly, it has as much to do with polar bears and ice caps as it does with warm tropical waters.

- When you lose ice over the Arctic ocean, it exposes dark water, and it doesn't bounce back that solar radiation.

So, the Arctic is becoming warmer, and there's less of a temperature difference between the Arctic and for Southern latitudes.

And that's having impacts on the jet stream and air circulation, where you have the jet stream moving wavier in some places and also slower.

And as a result, when you have air circulation patterns move slower, you can have this stalling of hurricanes.

- We're seeing a lot of storms that are stalling just on the coast raking them with whatever wind speeds are present.

And then, it's just slowly going inland and dumping out then all its precipitation, that's all of the worst things that could happen in a hurricane happening all together.

And that's what we saw with Harvey and Sally.

- Now, there's still some debate on this theory, but it's consistent with predictions made by researchers modeling the effects of climate change.

And we've seen it happen every year since Harvey with Florence, Dorian, Sally, and Eta.

So, what can we do to prepare for more storms like this in the future?

Well, I talked to Dr. Anne Cope, who studies ways to make homes more weather resilient.

I really just wanna hear from you a little bit about what you guys do over there at IBHS.

- Oh, sure, so we exist to figure out scientific ways to make buildings affordably more resilient.

Our Research Center (upbeat music) looks like a giant concrete block with 105 fans with a turntable right there in the middle.

We can put houses on there and we can turn 'em to face the wind in different directions, where we can recreate category three hurricanes, because we wanna see how they're gonna fail.

(wind howling) - So, what can people do to prepare for storms and to protect their homes and businesses?

- Make sure your house is as ready as it can be.

Get all the stuff out of the yard.

Kids' toys, big wheels, potted plants, stuff that can fly around and break your windows.

Those openings can be amazingly vulnerable.

Put those hurricane shutters up, make sure that you get to close all those interior doors right before you leave.

Because in case you do have a broken window, the wind and rain wants to get in, and go through the whole house and pop the roof off.

So, if you can close all those interior doors, even if you get one broken window, you can keep that compartmentalized to that one room, and not let mother nature go through your whole house.

The most important thing for any structure, and when you're facing strong winds, is the roof.

The roof is your number one line of defense against all of that storm, all of that wind driven rain.

Now, if you're in the market for a new roof, you wanna get a fortified roof, because you want the outer layer to be good and strong, wind resistant roof covering.

You want the right underlayment sealed roof deck to keep the water out.

And you wanna make sure that the structural pieces of the roof are well attached to the rest of the building.

If you have to evacuate because a hurricane is coming, take heed, get you and your family to safety.

- Where can people go if they can't evacuate?

What is the best place for people to be in their home, to be safe?

- Get yourself to the most interior spot that you have, away from windows, away from the outside walls.

Get yourself to the very middle, if you can.

Put your bike helmet on, get yourself like a mattress or something to protect yourself from debris, get yourself to the inside with as much between you and mother nature as you can get.

- I think it's safe to say after the 2020 hurricane season, which has been the most active on record, it's worth preparing ourselves and our homes for the fury of nature.

Remember the best way to stay safe during a hurricane is to be prepared with an evacuation plan and route, and move quickly when evacuation orders are issued.

Also stay tuned for our upcoming episode on stocking your pantry and preparing a go-bag to make weathering a storm or evacuating more comfortable and safe.

Thanks for watching this episode of "Weathered".

If you liked it, don't forget to give us a thumbs up and subscribe so you never miss an episode.

See you guys next time.

(placid music)