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By Amanda Greenwood
Associate News Editor
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Thousands of residents across parts of southern Texas are being urged to limit outdoor activity after the National Weather Service (NWS) issued a heat advisory warning on Wednesday.
The alert is in effect from Wednesday afternoon into the evening, with forecasters warning that heat index values could reach between 111 and 116 degrees Fahrenheit. These elevated "feels like" temperatures are driven by a combination of high heat and humidity, creating conditions that significantly increase the risk of heat-related illness.
Extreme heat is one of the most dangerous weather hazards, primarily because it directly affects the human body's ability to regulate its temperature. When heat and humidity rise, the body's cooling system (sweating) becomes less effective. The core body temperature can then rise rapidly, which can increase the risk of heat exhaustion, dehydration and heat stroke, which can be fatal if left untreated.
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According to the NWS office in Brownsville, the advisory covers inland Kenedy, southern Hidalgo, inland Willacy and inland Cameron counties—including cities such as McAllen, Edinburg, Pharr, Mission, Weslaco, Raymondville, Brownsville, Harlingen and Sarita.
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How Hot Is 116 Degrees? Understanding the Heat Index
The temperatures cited by the NWS refer to the heat index, also known as the "apparent temperature," which is a measure of how hot it feels when humidity is factored in, according to the NWS.
In practical terms, this means the following:
- A heat index of 111-116 degrees Fahrenheit can occur when air temperatures are typically in the mid-to-upper 90s, combined with high humidity.
- Under these conditions, sweat doesn't evaporate as efficiently as normal, which prevents the body from cooling itself down, as it typically does.
- The NWS cautions that prolonged exposure to this level of heat falls into the "danger" category, where heat exhaustion is likely, and heat stroke becomes possible.
- Direct sunlight can make conditions even hotter, raising the perceived temperature by up to 15 degrees, according to the NWS.
How This Heat Compares to Normal Temperatures for May
Looking at average weather patterns for May compiled by Weather Spark and Current Results, the NWS's heat advisory level significantly exceeds what is typical for early May in this part of Texas.
For instance, in the Rio Grande Valley, average May high temperatures generally range from 87 to 92 degrees, with lows in the low 70s, and in cities such as Brownsville and McAllen, normal May highs typically fall between 90 and 92 degrees.
This means the current conditions—especially when factoring in humidity—are pushing perceived temperatures 20-25 degrees above what is normally expected.
Who Is Most at Risk and Why It Matters
The NWS warned that "hot temperatures and high humidity may cause heat illnesses to occur," urging residents to stay inside, in air-conditioned rooms, keep hydrated and check on vulnerable individuals.
According to the agency, heat index values above 103 degrees already pose a danger, with risks escalating quickly as temperatures climb.
Vulnerable groups include the following:
- Older adults
- Young children
- People with chronic illnesses
- Outdoor workers
How To Prepare for Extreme Heat
The NWS advises residents in affected areas to take precautions before the hottest part of the day arrives:
- Hydrate early and often, even if you are not thirsty.
- Plan activities for early morning or evening.
- Ensure access to air conditioning or cooling centers.
- Wear lightweight, loose-fitting clothing.
- Check on elderly neighbors and vulnerable individuals.
If working outdoors, employers and workers should schedule frequent breaks in shaded or air-conditioned areas.
What To Do During the Heat Advisory
During the heat advisory period through Wednesday afternoon, the NWS advises minimizing exposure to the climbing temperatures:
- Stay indoors in air-conditioned spaces whenever possible.
- Avoid direct sunlight, especially between 1 p.m. and 7 p.m.
- Never leave children or pets in vehicles.
- Watch for signs of heat-related illness, which include heavy sweating, dizziness, nausea and confusion.
Anyone showing signs of heat stroke—such as an extremely high body temperature above 103 degrees—should receive immediate medical attention, as it is considered a medical emergency.
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