Summer season started today. The days will be getting shorter from now on, and the nights longer, but both will be warmer than before. If you’ve had a birthday and said, like so many of us, “gosh, I can’t believe I’m this old now”, then you’ll need to pay special attention to the heat index.
It’s part of most weather forecasts. The heat index shows how warm the temperature feels to the human body. High humidity suppresses evaporation. The human body’s cooling system works through perspiration, which means fluid must evaporate from the skin to have a cooling effect. Wet spots on the shirt or blouse indicate that this isn’t happening completely, and we feel hotter than the thermometer reading would suggest.
Things can get very unpleasant toward the end of a hot afternoon, when the air is cooling and its relative humidity is increasing. For example, 82 degrees isn’t a worrisome temperature for most southerners. But at 85% relative humidity, the body feels like it’s 90 degrees. We can hope that we won’t see a heat wave like the one that paralyzed Europe in June 2019. France reported a record temperature of 115 degrees in Gallargues-Les-Montueux. That’s in the Gard Region of France’s Provence, normally an extremely pleasant area with a California-like climate. I have joyful memories of traveling there in warm but never exceedingly hot summer weather. If we were to hit a temperature like Gallargues had last year, enhanced with Georgia’s steady flow of moisture from the Gulf of Mexico, our heat index would literally be off the charts. Even at “just” 100 degrees, it takes only 65% humidity to bring the heat index to a scorching 136 degrees. At 94 Fahrenheit, the same humidity would already make us feel like it’s 114. Increasing age renders people more vulnerable to such stifling temperatures, which makes the heat index one of the most important items to watch in the forecast.
Wind has a cooling effect because it enhances perspiration. This produces a serious dehydration hazard for people exposed to hot airflow. Motorcyclists and bicyclists are often taken by surprise when the air, in spite of its pleasant feel, wicks great amounts of moisture out of the body. When the heat index is high, or if you’re riding on two wheels, drinking plenty of water is of the essence.
Rudi Kiefer, Ph.D., is a professor at Brenau University, teaching physical and health sciences on Brenau’s Georgia campuses and in China. His column appears Sundays and at gainesvilletimes.com.