Why Is the Southeast So Humid?

iStock
iStock

You don’t have to hop on a plane to visit the tropics when you live in the southeastern United States—it can often feel like you’re already there. It gets humid in this corner of the country. Not just regular humid, mind you, but so disgustingly moist that you can almost feel the air slosh across your skin as you walk out the front door. But what is it that makes the Southeast so humid compared to the rest of the country?

Mugginess during the summer is a problem just about everywhere you go in the United States. The corn fields of Iowa can see a higher dew point than a rainforest. But even there the steaminess doesn’t last as long as it does in the Southeast. Much of it has to do with the region’s proximity to the Gulf of Mexico, which usually feels like bathwater on a good day. The water in some parts of the Gulf of Mexico can heat up to 90°F during the peak of the summer, and the water isn’t quick to cool down once cold fronts start sweeping through in the fall and winter. The warmth of the Gulf and the Caribbean Sea to its south keep moisture in plentiful supply.

It’s not just the water itself that contributes to the mugginess. The water vapor over the ocean doesn’t migrate inland on its own—weather patterns drag it inland and keep it locked in place. Strong winds blowing counterclockwise around low-pressure systems often help bring this tropical moisture inland, especially during the cooler months when you expect to shiver rather than sweat. During the summer, though, persistent ridges of high pressure keep the southeast feeling gross with a moist southerly wind. These “heat domes” deflect most weather systems approaching from the west, basically locking the Southeast into a state of sultriness for weeks and even months at a time.

The constant moisture isn’t merely uncomfortable—it can be downright dangerous. The human body is able to cool itself when sweat evaporates from the surface of exposed skin. But sweat has a harder time evaporating when there’s too much moisture in the air, which could cause a person to overheat. This phenomenon is measured with the heat index, and it’s the cause of thousands of heat-related illnesses and deaths every year.

All of that moisture makes both day and night downright miserable. If you’ve ever been to the desert during the warmer months, you know firsthand that even on a day when the high temperature exceeds 100°F, the mercury can plummet once the Sun goes down and get chilly enough to require a light jacket. The wild temperature fluctuations in desert regions are due to the dryness of the air there. Moist air has a higher heat capacity, so it takes a lot longer to warm up and cool off.

Meanwhile, the gross humidity levels in the Southeast on most days keep it from getting excessively hot, but it also keeps the nights from cooling off very much. The lack of nighttime relief compounds the danger posed by heat and humidity.

Wayfair’s Fourth of July Clearance Sale Takes Up to 60 Percent Off Grills and Outdoor Furniture

Wayfair/Weber
Wayfair/Weber

This Fourth of July, Wayfair is making sure you can turn your backyard into an oasis while keeping your bank account intact with a clearance sale that features savings of up to 60 percent on essentials like chairs, hammocks, games, and grills. Take a look at some of the highlights below.

Outdoor Furniture

Brisbane bench from Wayfair
Brisbane/Wayfair

- Jericho 9-Foot Market Umbrella $92 (Save 15 percent)
- Woodstock Patio Chairs (Set of Two) $310 (Save 54 percent)
- Brisbane Wooden Storage Bench $243 (Save 62 percent)
- Kordell Nine-Piece Rattan Sectional Seating Group with Cushions $1800 (Save 27 percent)
- Nelsonville 12-Piece Multiple Chairs Seating Group $1860 (Save 56 percent)
- Collingswood Three-Piece Seating Group with Cushions $410 (Save 33 percent)

Grills and Accessories

Dyna-Glo electric smoker.
Dyna-Glo/Wayfair

- Spirit® II E-310 Gas Grill $479 (Save 17 percent)
- Portable Three-Burner Propane Gas Grill $104 (Save 20 percent)
- Digital Bluetooth Electric Smoker $224 (Save 25 percent)
- Cuisinart Grilling Tool Set $38 (Save 5 percent)

Outdoor games

American flag cornhole game.
GoSports

- American Flag Cornhole Board $57 (Save 19 percent)
- Giant Four in a Row Game $30 (Save 6 percent)
- Giant Jenga Game $119 (Save 30 percent)

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Expeditions Gather Climate Change Clues on Mount Everest in Two New Documentaries

Team members climb up a slope during the expedition to find Sandy Irvine's remains on Mount Everest.
Team members climb up a slope during the expedition to find Sandy Irvine's remains on Mount Everest.
Matt Irving/National Geographic

Two one-hour documentaries premiering tonight reveal what Mount Everest is really like—and what scientists can learn from studying it.

Both docs are produced by and airing on National Geographic. In Lost on Everest, premiering at 9 p.m. EDT, climber Mark Synnott and Nat Geo photographer Renan Ozturk lead a team of seasoned mountaineers on a mission to discover what happened to Andrew “Sandy” Irvine, who vanished with fellow explorer George Mallory during the first Everest climb in June 1924. While Mallory’s body was located by a BBC-sponsored operation in 1999, Irvine’s exact fate has remained a mystery for nearly a century since his disappearance. As Synnott and his companions search for evidence, they encounter their own harrowing set of obstacles, from hurricane-force winds to medical emergencies.

Climbers on Mount Everest
Climbers ascend the Khumbu Icefall, a notoriously dangerous section of the summit route.
Mark Fisher/National Geographic Society

But Mount Everest isn’t only a challenge for adventure-seekers and intrepid investigators—it also holds thousands of years’ worth of information about how climate change has altered the environment, which can help scientists predict its future effects. In Expedition Everest, airing at 10 p.m. EDT, actor Tate Donovan narrates the journey of an international group of scientists and climbers with an ambitious set of data-collecting objectives.

One task is to use drones, laser scanners, and cameras to capture footage of every inch of the ascent, so researchers can create a 360-degree portrait of the mountain and track how glacial melt alters the landscape in the coming years. Since the Himalayas contain the water supply for roughly one-fourth of the world’s population, the increase in glacial melt—which has already doubled since 2000—could threaten the futures of billions of people living in the region.

Scientists drill ice cores on Mount Everest
Mariusz Potocki and members of the National Geographic and Rolex Perpetual Planet Everest Expedition team collect the highest-ever ice core at 8020 meters (26,312 feet) near the South Col of Everest.
Dirk Collins/National Geographic Society

Even more immediate is the risk of flash floods, which are difficult to predict without a constant feed of weather data from high altitudes. Another goal of the expedition is to install weather stations at five locations along the climbing route, which will monitor temperature, humidity, air pressure, wind speed, and other factors that help alert meteorologists to an impending flood.

Some researchers have joined the expedition to drill deep into the ice at an altitude above 8000 meters (26,000 feet)—Mount Everest's "death zone"—and collect ice cores. These long tubes of ice reveal how the atmosphere has changed over thousands of years. Others are collecting similar cores of sediment at the bottom of a lake, as well as examining how plant and animal life has adapted to the warming temperatures and rising water levels.

Overall, Expedition Everest illustrates how the Himalayas function as an early indicator of what climate change will do to other places.

As climate scientist Anton Seimon explains in the documentary, “We’re getting a window into what the rest of the world is starting to experience—and likely to experience in growing proportions.”

You can watch the double feature tonight, June 30, at 9 p.m. EDT on National Geographic.