Yes, 'corn sweat' is real and it can enhance brutal Midwestern humidity

A dangerous heat wave gripping portions of the central United States made headlines this week for two words: corn sweat.

Yes, 'corn sweat' is a real thing that can have a real impact on the weather.

Daytime highs soaring into the middle to upper 90s is brutal any day, but throw in humidity and it's unbearable even for folks who are acclimated to hot temperatures. That's what we're seeing across the Midwest this week. As of about 2:30 p.m. on Tuesday, the temperature at Chicago O'Hare was a record 98°F with a heat index of 114°F. 

That's hot! A major factor driving this excessive heat is the excessive humidity strangling the area like a wet blanket. The best measure of moisture in the air is the dew point, which is a good proxy for how much moisture is present in the air at any given time.

Relative humidity—"the humidity is 95%!"—is really only useful for forecasting fog and wildfires. If you want to measure comfort, dew point is the way to go. 

Any dew point below 50°F is generally dry and comfortable. Things get noticeably humid when the dew point climbs above 60°F. It's downright muggy when the dew point reaches 65°F, and you're in tropical territory when the dew point hits 70°F or higher.

Dew points climbed above 80°F throughout Iowa, Illinois, Minnesota, and Wisconsin during the day Monday. That's an atrocious, strangling level of humidity, especially when combined with high temperatures. 

It's uncommon to see dew points climb toward 80°F outside of tropical rainforests and the U.S. Midwest roughly for the same reason: evapotranspiration, or the infamous "corn sweat."

Plants consume a tremendous amount of water in order to survive and thrive. Excess water evaporates out of the plants into the atmosphere, raising moisture levels to heights rarely seen outside of areas blanketed by lush vegetation.

Why is corn sweat such a big deal and not, say, "kudzu sweat" from those invasive leafy vines that blanket the southern states? Corn gives off a ton of water. "An acre of corn gives off about 3,000-4,000 gallons (11,400-15,100 liters) of water each day," according to the USGS. And we have vast swaths of the Midwest carpeted with cornfields churning out that much water vapor every day.

[Top image courtesy of Unsplash]

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Dangerous rip currents expected along U.S. East Coast as Ernesto passes by

Hurricane Ernesto will come dangerously close to Bermuda this weekend as it passes through the western Atlantic Ocean. While the storm itself won't hit the United States, the storm's rough surf will reach the East Coast and bring a threat for dangerous rip currents from Florida to Maine.

Ernesto is strengthening on approach to the tiny island of Bermuda, which sits about 650 miles east of South Carolina. 

Forecasters expect the storm to come close to major hurricane status before brushing just west of Bermuda Friday night into Saturday, putting the island in a vulnerable position for damaging winds and storm surge flooding.

The storm will continue heading north-northeast through the western Atlantic and eventually threaten Newfoundland with high winds and heavy rain by early next week. 

Even though the storm is going to miss the United States, folks along the coast will experience some dangerous impacts from this storm. Hurricanes generate high waves that can travel hundreds and even thousands of miles away from the storm. These waves bring with them a risk for rip currents beginning tonight and lasting through the weekend.

Rip currents are strong channels of water that pull away from the beach and directly out to sea. They don't pull you under like in the movies—they drag you away from safe shores in a hurry. People can quickly exhaust themselves fighting against the current, and that's when they run the risk of drowning.

Just about every beach from Florida to Maine has a risk for rip currents this weekend, especially in places like North Carolina, Virginia, and the Delmarva Peninsula.

Source: NOAA

Please stay out of the water if told to do so by local officials. They're not kidding when they say it's unsafe to swim. Lifeguards on a single beach can conduct dozens of water rescues every day as a result of people failing to heed red flag warnings for rip currents.

Rip currents look like calm patches of water amid otherwise rough surf. This apparent serenity lulls swimmers into a false sense of complacency, luring them into the ocean only to find themselves caught in a rip current.

If you're ever caught in a rip current, don't panic. Calmly signal for help. If you're a capable swimmer, swim parallel to the shore until the current stops dragging you out, then swim straight back to the beach. If you can't swim, tread water until help arrives. Don't struggle directly against the current. It's too strong for even the strongest swimmer to conquer.

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Major flood threat to develop this week as tropical storm stalls over southeast

A major flood threat will develop this week as a brewing tropical storm is expected to stall-out over the southeastern United States.

Forecasters expect Tropical Storm Debby to rapidly get its act together in the eastern Gulf of Mexico through the weekend, making landfall in Florida's Big Bend region as a strong tropical storm early Monday.

After landfall, the storm will slowly track into Georgia through Tuesday before emerging off the coast into the western Atlantic Ocean by late Tuesday night or early Wednesday morning.

From there, though, this system isn't going to go anywhere in a hurry.

SOURCE: Tropical Tidbits

Two large ridges of high pressure will essentially pin the storm in place after landfall. One ridge over the western Atlantic and another over the south-central U.S. will act like barriers that the storm won't easily squeeze through.

As a result, Debby will meander off the southeastern coast for several days before an opening allows the storm to finally begin pulling north later in the week.

A stalled tropical system dumping copious amounts of rain over the same areas is a story we've seen time and time again in recent years. This won't be any exception. The Weather Prediction Center calls for a large swath of 5-10 inches of rain across northern Florida, eastern Georgia, and the eastern Carolinas. More than 10 inches of rain is possible along the storm's path proper.

This much rain falling in a relatively short period of time is a recipe for flash flooding. Most deaths from landfalling tropical systems are the result of motorists drowning in flash floods. If you're in the area, please don't try to drive across a flooded roadway. It's impossible to tell how deep the water is until it's too late.

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