I’m not from this area of the country, but I have experienced some really hot summers in other parts of the US. But nothing really compares to this weather. It is unbearable in every way. I feel like I need a shower just sitting here and dehydration is inevitable.
Why is it so brutal here!?
In: Planetary Science
Humidity and temperature are correlated. Our *perception* of temperature is affected by humidity levels. When the air humidity is very high, the perspiration process is impeded; it will be harder for water to be evaporated from our skin into the air since the air is already quite moist (full of water). Hence our ability to cool will be obstructed and we will feel that the temperature is hotter than it actually is.
This is why you will occasionally hear someone in a desert say, “At least it’s a dry heat.” If two regions have identical temperature, the region with the higher humidity will be much more unpleasant and even dangerous.
It’s the moisture in the air. The south isn’t just hot, it is extremely humid. Normally you reduce body temperature by sweating, which quickly evaporates and cools you down. The problem with the southern US is that the air gets near saturation, so your sweat doesn’t evaporate nearly as quickly. So your clothes become a soggy mess and you feel gross.
The good news is that a dehumidifier will help your home feel much more pleasant during the summer months, fight against mold, and assist your air conditioning system (drier air is much easier to cool).
The bad news is that summer lasts quite a while in the south. It can gradually rob you of energy as the nights don’t quite cool down for weeks at a time. Hydration is indeed a key thing to pay attention to, as well as electrolytes if you’ve been sweating.
Just to put it in perspective the Gulf Coast is at the same latitude as the northern edges of the Sahara Desert in Africa and at the same latitude as the Arabian desert in the Middle East.
The Earth tilts at a 23.5 degree angle. So at the end of June, the areas at exactly 23.5 degrees latitude (also called the Tropic of Cancer) in the Northern Hemisphere are pointing the closest to the sun, and receiving direct rays from the sun. This will naturally make the areas around this latitude warmer. For reference, Miami is at 25.7 degrees, Houston is at 29.7, New Orleans is at 30.0. Cairo, Egypt is also at 30.0 latitude. Just for reference, other hot areas like Phoenix is 33.4 and Las Vegas is at 36.2.
Another factor is how the Atlantic currents work. In the Northern Hemisphere, currents spin clockwise. That means the waters near the equator in the Atlantic are pushed towards the Caribbean Sea and Gulf of Mexico and towards Florida, and then up the US Atlantic coast. That means the Caribbean, the Gulf of Mexico, and the southern Atlantic coast is filled with very warm water, which also heats the air. Water also cools much slower than air, so the water stays warm throughout the summer. Also having all of that warm water from the Gulf makes air very humid in the Southeast US. Humid air takes much longer to cool than dry air, because water takes longer to cool than air. Contrast that to the western US, where the Pacific current also spins clockwise, but that means the Pacific coast of the US has water coming from Alaska being pushed down. Yes, this water heats up somewhat, but even in places like LA and San Diego, the Pacific is still very cool. I just checked, the temperature of the Pacific in San Diego is 64 degrees right now. It is 81 in Miami. It is 87 in Galveston (next to Houston on the Gulf Coast). This huge difference in water temperature makes a huge difference in air temperature.
It’s the humidity.
Humans don’t actually have a great sense for absolute temperature. From a biological perspective, we don’t really need to. What we need to know is how well our bodies are *shedding* heat. This is important because when you’re chasing your food across the African savannah, you need to know how well you are shedding heat so you can pace yourself and run down that happy meal that is running away at a rapid pace.
Humans shed heat by sweating. More specifically, we sweat, which then evaporates. This process carries away a tremendous amount of heat when compared to simply radiating heat away like animals that don’t sweat.
The drier the air, the more moisture it can absorb. So when the air is dry, our sweat evaporates quickly and we feel very cool
When the air is already full of moisture, our sweat evaporates slowly, and by consequence we feel hotter.
This means that our bodies are less able to cool off when it is humid. Our brains signal to us that this is a problem by making us feel miserable. It’s a warning: hey, conditions really suck for physical activity, so maybe chill out a bit.
We regulate our temperature by sweating when we’re hot and when that sweat evaporates, it cools us off a little. Humidity is a measure of how much water is in the air and when it’s high, sweat doesn’t want to evaporate because the air already has plenty of water, sort of like trying to dry yourself with a wet towel. The south is *very* humid, so when it’s hot, we sweat like normal, but because that sweat isn’t evaporating like it’s supposed to, it doesn’t cool us off as well as it should.
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