There’s hot, and then there’s “South Texas” hot. On Tuesday afternoon, San Antonio’s heat index value hit 117 degrees, which is the highest heat index temperature ever recorded in the city. It surpassed the previous record of 116 degrees, set just last year on June 20, 2023.

The heat index is calculated by using both temperature and dew point, which is a measure of how much moisture is in the air. At 2:54 p.m., the temperature at San Antonio International Airport was 100.4 degrees. Combined with a very high dew point of 77 degrees, we get a heat index value of 117 degrees.

Essentially, the heat index helps to measure the body’s ability to cool itself off. On a normal day, the body cools itself through the evaporation of sweat from our skin. However, on especially humid days, the sweat on your skin does not evaporate as effectively, making you feel hotter.

Keep in mind that heat index records are not “official” records kept by the National Weather Service. This is because some weather observation sites use exact measurements while others are automatically rounded off. After the heat index calculations are done, this can result in errors of 1-2 degrees.

The actual air temperature reached 103 degrees in San Antonio on Tuesday. This broke the daily record of 100 degrees, which was set over 100 years ago, in 1916.

Dangerous heat will continue this week across South Texas. Heat index values are expected to reach close to 110 degrees or higher each day for the rest of the week. If you have to be outside, remember to stay properly hydrated and take breaks away from the sun.