We had one of the coolest, most pleasant Mays ever this year, but now we’re paying for it. Last year, I recorded a max heat index in Jackson of 107 two or three times. This year, I’ve seen 110 once and 109 a couple of times.
One of those days set an all-time high temperature record for that day of the year. Another day set a record high low temperature. No doubt, it’s been hot!
We all know Mississippi is hot in the summer, but how does our heat stack up against the hottest cities in the world?
Factoring in heat index, using centrally-located Jackson as a guide, Mississippi is about as hot as any place in the world in July and August.
The National Weather Service describes the heat index like so: “The heat index, also known as the apparent temperature, is what the temperature feels like to the human body when relative humidity is combined with the air temperature. This has important considerations for the human body's comfort. When the body gets too hot, it begins to perspire or sweat to cool itself off. If the perspiration is not able to evaporate, the body cannot regulate its temperature. When the atmospheric moisture content (i.e. relative humidity) is high, the rate of evaporation from the body decreases. In other words, the human body feels warmer in humid conditions.”
I tried searching Google for “cities with the highest heat index in the world,” but couldn’t find a list. So I made my own.
I Googled “hottest cities in the world,” made my list and then applied the heat index. For temperature, I used the month with the hottest average temperature. For humidity, I used the average monthly humidity.It would have been preferable to use the humidity level directly associated with the hottest average temperature, but that data wasn’t available. So I had to use the monthly humidity average as a proxy. Since humidity goes down as temperature goes up, using the monthly average humidity creates a higher-than-actual heat index, but it still works for comparing cities.
Jackson is not the hottest city in the world, but it’s right up there with the hottest of them. Phoenix is only two degrees hotter than Jackson based on heat index.
Manaus, Brazil, in the heart of the Amazon jungle, is cooler than Jackson. In fact, Jackson is hotter than every city in South America and every city in Africa.
To have a really high heat index several factors must combine: First the city has to be at sea level. Altitude lowers temperatures. Second, the city has to be far enough away from the equator to get extra hours of sunlight in the summer. Third, it helps to be humid.
Most of Africa and South America are at a higher altitude than sea level. Also, the equator never gets more than 12 hours of sunlight. Jackson gets 14 hours in the summer.
As you move farther north than Jackson, say Memphis, the sunlight is less direct caused by the tilt of the earth. Jackson is right in the sweet spot for producing high, humid temperatures.
Alvaz, Iran, is the only dry city to be in the top five hottest cities. It took temperatures of 117.2 and still didn’t beat Chennai, India’s heat index.
Stateside, it’s the Texas cities that are the hottest: Houston, San Antonio and Austin. Temps are higher in both San Antonio and Austin, but the Houston humidity wins the day.
Note that Jackson is hotter than both Memphis or New Orleans. Memphis has less humidity and New Orleans has lower temperatures.
As a check, I used two different international weather agencies: the European Center for Medium Range Forecasts and the World Meteorological Organization — both world-class organizations. Yet there was a huge amount of variability in the temperatures and humidity measurements.
This makes me skeptical of the accuracy of long-range global temperature forecasting models if we can’t even agree on what the temperature is right now.
