May, June and July have all been San Antonio’s hottest on record. And while it’s too early to say whether August will be another record-breaker, it looks likely. 

Why is it so dang hot?

There are three reasons this heat wave is hitting Central Texas particularly hard, said State Climatologist John Nielsen-Gammon: low moisture in the soil, weather patterns bringing in dry air from urban Mexico and climate change.

The weather phenomenon known as La Niña contributed to dry conditions this winter and spring, he said, leaving South Texas more susceptible to the heat going into summer. San Antonio experienced its second driest July on record last month, according to the National Weather Service.

“The fact that it’s been so dry recently means that temperatures were able to get hotter faster because we lose that cooling effect of evaporation,” Nielsen-Gammon said. “La Niña … contributed to dry conditions this winter and spring, which has left us more susceptible going into the summer.”

La Niña is the cold phase of the El Niño Southern Oscillation, a cycle of ocean temperatures that influences weather around the globe. During La Niña, sea surface temperatures in the southern Pacific Ocean hover at a temperature lower than average.

In Texas, La Niña tends to cause warmer and drier conditions than normal because of its influence on the jet stream. La Niña conditions are expected to continue into the fall.

Weather patterns also are sweeping in torrid air from urban Mexico, pushing temperatures even higher here in Texas, Nielsen-Gammon said.

And while summer heatwaves are typical in Texas, climate change is influencing their severity, Nielsen-Gammon said. As weather conditions become more severe due to climate change, drier and longer droughts are likely to become more prevalent, he added.

According to a report that Nielsen-Gammon and his team published in October, the average annual Texas surface temperature in 2036 is expected to be 3 degrees warmer than the 1950-1999 average and 1.8 degrees warmer than the 1991-2020 average due to climate change.

The Electric Reliability Council of Texas (ERCOT) has broken demand records at least nine times so far this summer, including July 18, when it hit a new unofficial peak demand of 78.9 gigawatts, beating the previous record, hit just three days earlier, of 78.2 gigawatts.

One megawatt is enough electricity to power 200 Texas homes on a summer day. 

CPS Energy has repeatedly assured customers that it has enough power to meet demand, although it too has called for conservation, in large part to help keep the grid stable. The utility hit its own new peak demand this week, officials said.

Heat is by far the deadliest weather condition. Given the region’s prolonged extreme temperatures, National Weather Service meteorologist Nick Hampshire said, those who spend time outside should be aware of how heat stress can affect the body, take frequent breaks and drink plenty of water.

Local officials are urging residents to take care to stay cool and safe, and to keep an eye on vulnerable populations like children, the elderly and pets. City libraries and community centers are open as cooling centers.

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Lindsey Carnett

Lindsey Carnett covers the environment, science and utilities for the San Antonio Report.