Hurricane Harvey Broke Multiple Weather Records

Hurricane Harvey will be remembered as one of the most destructive hurricanes to ever strike the United States. The storm erupted from a weak tropical wave into a category 4 hurricane in just three days, coming ashore near Corpus Christi, Texas, late in the evening on August 25. Such a powerful storm hitting land is normally a catastrophe in its own right, but the tragedy that followed this storm wasn't caused by the wind or the ocean—it was the rain, and lots of it. Texas endured one of the worst flooding events in American history after Harvey lingered over the state for nearly a week and dropped more than three feet of rain on Houston, the country's fourth-largest city.

The hurricane's intense winds and storm surge devastated some of Texas's coastal communities near Corpus Christi, including the small towns of Rockport and Port Aransas. Wind gusts peaked above 100 mph across most areas in the path of the storm's eye. Weather instruments measured winds as high as 132 mph near Port Aransas as the eye came ashore on August 25. Hundreds of homes and businesses were damaged or destroyed by the storm's intense winds.

Under normal circumstances, a hurricane would make landfall and move out of the area within 24 hours. Late-night hurricanes typically end with residents surveying the damage by the first light of day. Harvey was not one of those storms. The storm stalled out over Texas after making landfall, meandering over the same area before reemerging over the Gulf of Mexico to make a second landfall in Louisiana five days later.


Observed rainfall between August 23, 2017 and August 30, 2017.
Dennis Mersereau

The bulk of Harvey's unprecedented rains fell on the Houston metropolitan area, a region that's notorious for flooding due to its geography and heavily urbanized landscape. Water has few places to go when heavy rain falls on such impermeable land. The influx of water quickly overwhelms narrow waterways and outdated drainage systems, leading to frequent stream and street flooding. The factor that separates this storm from previous flooding disasters in southeastern Texas is that this rain was worse than anything in recorded history, more than doubling the rainfall totals seen during the infamous floods unleashed by Tropical Storm Allison in 2001.

Houston's George Bush Intercontinental Airport recorded 32.17 inches of rain between August 25 and August 29, while Houston's Hobby Airport—where the runways were flooded out for a time during the height of the storm—saw 38.22 inches of rain over the same period. The two airports both average about 50 inches of rain in a normal year. Various rain gauges around the area measured totals even higher than the two airports. A rain gauge in Cedar Bayou, Texas, just north of Galveston Bay, saw more than 52 inches of rain in five days.

Emergency officials and volunteers performed thousands of water rescues for people stranded in their homes and vehicles as the waters rose. The exact number of fatalities won't be known until crews can search every vehicle and home once the waters recede. The Washington Post quoted local officials as saying that floodwaters covered more than 30 percent of Harris County, home to Houston, during the height of the ordeal.

The perfect mix of ingredients came together to make Hurricane Harvey a historic disaster. Tropical cyclones require warm water, low wind shear, and ample moisture to develop and thrive. Once the tropical wave that seeded Hurricane Harvey's development hit the Gulf of Mexico, it had all three of those ingredients in abundance. The storm rapidly intensified under these perfect conditions, strengthening right up until it came ashore. But what made the storm especially destructive is that it didn't move after landfall.

Tropical storms and hurricanes are steered by winds through the atmosphere. Weaker storms are driven by prevailing winds close to the surface while strong storms like Harvey are steered by winds throughout the entire depth of the atmosphere. Harvey's path took it right into an area where there were no steering currents to force the storm to keep moving inland and away from Texas. The calm pattern around Harvey kept it locked in place, forcing the storm to meander for days after landfall, slowly tracking in a loop before making its way back out over the water.

Preliminary measurements show that Hurricane Harvey was the wettest tropical cyclone in American history, producing several reports of rainfall that break the previous all-time record. Cedar Bayou, Texas, will hold the unfortunate distinction of most rain ever recorded during a tropical cyclone, having measured 51.88 inches of rain by the afternoon of August 29. Even if that reading doesn't hold up to scrutiny, there were several more that beat the previous record of 48.00 inches set in Tropical Storm Amelia back in August 1978. Just over 49 inches of rain fell on a gauge near Pearland, Texas, a city that lies about halfway between Houston and Galveston.

Houston wasn't the only area devastated by the heavy rain. Houston gets the most coverage because it's home to the most people, but the scenes that played out there also unfolded in countless small towns and communities across the region. Extreme rainfall totals greater than three feet extended east of the metro area into southwestern Louisiana. The Texas cities of Beaumont and Port Arthur, which lie near the state line with Louisiana, saw more rain than Houston proper. The airport in Port Arthur measured nearly four feet of rain during the storm.

The rainfall isn't the only record set by Harvey. The storm put an end to the unprecedented streak of days without a major hurricane making landfall in the United States. The last hurricane rated category 3 or stronger to strike the country was Hurricane Wilma back in October 2005. Harvey was also the strongest hurricane to hit Texas since the 1960s.

Harvey wasn't the absolute worst case scenario for a hurricane hitting the Houston area, but it was a close second. Harvey will be remembered for its rainfall the same way Hurricanes Katrina and Sandy are remembered for their storm surge. This storm would have been magnitudes worse if it had made landfall in Houston proper rather than 150 miles down the coast. Category 4 winds and storm surge funneling into Galveston Bay would have made this an unimaginable tragedy, but nearly four feet of rain in five days comes pretty close.

Why Does Humidity Make Us Feel Hotter?

Tomwang112/iStock via Getty Images
Tomwang112/iStock via Getty Images

With temperatures spiking around the country, we thought it might be a good time to answer some questions about the heat index—and why humidity makes us feel hotter.

Why does humidity make us feel hotter?

To answer that question, we need to talk about getting sweaty.

As you probably remember from your high school biology class, one of the ways our bodies cool themselves is by sweating. The sweat then evaporates from our skin, and it carries heat away from the body as it leaves.

Humidity throws a wrench in that system of evaporative cooling, though. As relative humidity increases, the evaporation of sweat from our skin slows down. Instead, the sweat just drips off of us, which leaves us with all of the stinkiness and none of the cooling effect. Thus, when the humidity spikes, our bodies effectively lose a key tool that could normally be used to cool us down.

What's relative about relative humidity?

We all know that humidity refers to the amount of water contained in the air. However, as the air’s temperature changes, so does the amount of water the air can hold. (Air can hold more water vapor as the temperature heats up.) Relative humidity compares the actual humidity to the maximum amount of water vapor the air can hold at any given temperature.

Whose idea was the heat index?

While the notion of humidity making days feel warmer is painfully apparent to anyone who has ever been outside on a soupy day, our current system owes a big debt to Robert G. Steadman, an academic textile researcher. In a 1979 research paper called, “An Assessment of Sultriness, Parts I and II,” Steadman laid out the basic factors that would affect how hot a person felt under a given set of conditions, and meteorologists soon used his work to derive a simplified formula for calculating heat index.

The formula is long and cumbersome, but luckily it can be transformed into easy-to-read charts. Today your local meteorologist just needs to know the air temperature and the relative humidity, and the chart will tell him or her the rest.

Is the heat index calculation the same for everyone?

Not quite, but it’s close. Steadman’s original research was founded on the idea of a “typical” person who was outdoors under a very precise set of conditions. Specifically, Steadman’s everyman was 5’7” tall, weighed 147 pounds, wore long pants and a short-sleeved shirt, and was walking at just over three miles per hour into a slight breeze in the shade. Any deviations from these conditions will affect how the heat/humidity combo feels to a certain person.

What difference does being in the shade make?

Quite a big one. All of the National Weather Service’s charts for calculating the heat index make the reasonable assumption that folks will look for shade when it’s oppressively hot and muggy out. Direct sunlight can add up to 15 degrees to the calculated heat index.

How does wind affect how dangerous the heat is?

Normally, when we think of wind on a hot day, we think of a nice, cooling breeze. That’s the normal state of affairs, but when the weather is really, really hot—think high-90s hot—a dry wind actually heats us up. When it’s that hot out, wind actually draws sweat away from our bodies before it can evaporate to help cool us down. Thanks to this effect, what might have been a cool breeze acts more like a convection oven.

When should I start worrying about high heat index readings?

The National Weather Service has a handy four-tiered system to tell you how dire the heat situation is. At the most severe level, when the heat index is over 130, that's classified as "Extreme Danger" and the risk of heat stroke is highly likely with continued exposure. Things get less scary as you move down the ladder, but even on "Danger" days, when the heat index ranges from 105 to 130, you probably don’t want to be outside. According to the service, that’s when prolonged exposure and/or physical activity make sunstroke, heat cramps, and heat exhaustion likely, while heat stroke is possible.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

This article has been updated for 2019.

Chimpanzees Bond by Watching Movies Together, Too

Windzepher/iStock via Getty Images
Windzepher/iStock via Getty Images

Scientists at the Wolfgang Kohler Primate Research Center in Germany recently discovered that, like humans, chimpanzees bond when they watch movies together, the BBC reports.

In the study, published in Proceedings of the Royal Society B, researchers stationed pairs of chimpanzees in front of screens that showed a video of a family of chimps playing with a young chimp. They found that afterward, the chimps would spend more time grooming and interacting with each other—or simply being in the same part of the room—than they would without having watched the video.

They gave the chimps fruit juice to keep them calm and occupied while they viewed the video, and they chose a subject that chimps have previously proven to be most interested in: other chimps. They also used eye trackers to ensure the chimps were actually watching the video. If you’ve ever watched a movie with friends, you might notice similarities between the chimps’ experience and your own. Drinks (and snacks) also keep us calm and occupied while we watch, and we like to watch movies about other humans. Since this study only showed that chimps bond over programs about their own species, we don’t know if it would work the same way if they watched something completely unrelated to them, like humans do—say, The Lion King.

Bonding through shared experiences was thought to be one of the traits that make us uniquely human, and some researchers have argued that other species don’t have the psychological mechanisms to realize that they’re even sharing an experience with another. This study suggests that social activities for apes don’t just serve utilitarian purposes like traveling together for safety, and that they’re capable of a more human-like social closeness.

The part that is uniquely human about this study is the fact that they were studying the effect of a screen, as opposed to something less man-made. The chimps in question have participated in other studies, so they may be more accustomed to that technology than wild apes. But the study demonstrates that we’re not the only species capable of social interaction for the sake of social interaction.

[h/t BBC]

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