San Antonio broke its all-time high temperature record for July on Monday as triple-digit temperatures scorch South Texas amid a long-term trend of rising summer heat.

The National Weather Service is urging people to stay hydrated, seek shade, check up on residents without air conditioning, and never leave children or pets locked in unattended vehicles. The weather service on Monday issued a rare excessive heat warning, which requires a temperature forecast of 105 degrees or higher or a predicted heat index of 113 degrees or above.

“We don’t generally issue those very often,” NWS meteorologist Eric Platt said of that type of warning.

A weather station at the San Antonio International Airport recorded 107 degrees Monday, beating the previous record for this month of 106 degrees set on July 19, 1989. It also shattered the record for July 13 of 102 degrees set in 2013.

In response to the heat wave, the City of San Antonio opened three new cooling centers at Carver Library, Collins Garden Library, and Mission Library from noon to 7 p.m. Monday through Friday. The City operates 27 community centers, senior centers, and libraries as refuges for people who don’t have access to air conditioning to shelter during the heat of the afternoon.

Platt confirmed that a high-pressure ridge is responsible for the heat wave sending temperatures as high as 112 degrees Monday in the border cities of Del Rio. This high-pressure ridge – and the hot, stagnant weather it generates – is common during the height of summer in South Texas.

However, the triple-digit weather of July has already broken records, including an all-time high temperature for July 10 in San Antonio of 102 degrees, set in 1917. This year, the temperature reached 103 degrees that day, setting a new record, Platt said.

The hot temperatures come during a long-term warming trend that climate scientists have tied to mankind’s use of coal, oil, and natural gas and the destruction of greenhouse gas-trapping forests to make space for agriculture and urban development.

Globally, 2020 is “virtually certain” to be among the top 10 hottest years on record, according to the National Oceanic and Atmospheric Administration, along with every other year since 2013. All of the top 10 hottest years have occurred after 1997.

In San Antonio, average summer temperatures have gone up by 3.3 degrees since the 1970s, according to an analysis of NOAA data by the journalism nonprofit Climate Central. That’s led to more hot days, increasing from 271 days of 100-degree-plus temperatures in the 1970s to 669 days in the 2010s.

San Antonio has seen a rise of the number of 100-degree-plus days per decade from 271 days in the 1970s to 669 days in the 2010s.
San Antonio has seen a rise in the number of 100-degree-plus days per decade from 271 days in the 1970s to 669 days in the 2010s. Credit: Courtesy / Climate Central

The mercury will only continue rising over the coming decades, according to climate forecasts.

From 1971 through 2000, San Antonio sweated through only an average of seven days per year of triple-digit weather. That could rise from an average of 30 per year during the period of 2011 to 2040 to upwards of 60 days per year during the period of 2040 through 2070, according to climate modeling by University of Texas at San Antonio professor Hatim Sharif.

In the short term, temperatures should drop a few degrees compared to Monday, according to local forecasters. The NWS is forecasting a high temperature of 105 degrees in San Antonio Tuesday and 101 degrees Wednesday, before dropping down to a high of 99 degrees later in the week.

“I certainly don’t want people to let their guard down,” Platt said. “It’s still going to be hot.”

Brendan Gibbons

Brendan Gibbons

Brendan Gibbons is the San Antonio Report's environment and energy reporter.