Hibernating in the air conditioning

Published 9:30 am Saturday, August 21, 2021

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By Skip Rigney

Some bears hibernate during winter. Some humans in the Deep South hibernate during summer. Both the bears and the humans move inside to escape harsh outdoor temperatures. In south Mississippi, we don’t have the cool, dark caves favored by the bears. Instead, we are blessed to have air conditioning.

Our air conditioners will be working overtime this weekend to overcome some of the most oppressive heat and humidity that has affected our area this summer. The last couple of days have been uncomfortable enough, but outdoor temperatures Saturday and Sunday are forecast to climb a degree or two higher into the middle to upper 90s.

Humidity will be very high as reflected by dew point temperatures in the 70s. High humidity hinders the human body’s ability to cool off through the evaporation of sweat. That reduced cooling capacity is accounted for in the “heat index” or “apparent temperature.” Heat indices have crept to between 105 and 110 degrees since Wednesday. This weekend they could creep above 110 for a few hours in the afternoons.

All of this adds up to a likely continuation of heat advisories from the National Weather Service in Slidell during the next couple of days. Heat advisory impacts and precautions from the NWS are worth repeating. To avoid heat illnesses, “drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors. Young children and pets should never be left unattended in vehicles under any circumstances.”

Other NWS recommendations include taking extra precautions if you work or spend time outside and rescheduling strenuous activities to early morning or evening. Also, “if anyone is overcome by heat, they should be moved to a cool and shaded location. Heat stroke is an emergency! Call 911.”

Statistically speaking, the daily average temperature in Pearl River County, based on data from 1991-2020, inches down ever so slowly during August after reaching its annual maximum early in the month. That doesn’t change the fact that of the 99 hottest 3-day periods in the historical record for Poplarville, 21 have occurred in the latter half of August, more than any other two-week period of the summer.

The most immediate cause of this weekend’s heat is a dome of high pressure in the middle and upper altitudes of the atmosphere stretching from Missouri into the Gulf of Mexico and from the southern Great Plains to the southern Appalachians. The sinking air within the high not only warms as it descends, it also pushes back against the hot air from near the earth’s surface whose natural tendency is to rise. That makes it harder for clouds to grow tall enough to produce showers. So, there’s only a slight chance of isolated thunderstorms today. The chance of thunderstorms increases to about 40 percent late Sunday afternoon and evening, as a disturbance rides down the eastern edge of the high from our north and east.

One upside of this hot, high pressure system is that it is shielding us from tropical cyclones. On Friday, the circulation around the high steered Grace into Mexico and blocked Henri in the western Atlantic. Henri is now being drawn northward toward New York and New England by the circulation around low pressure in the middle and upper atmosphere over Virginia.