Excessive Heat in Willacy, Texas

Harlingen Valley International Airport (KHRL) recorded heat indices between 117-125F for 4 hours, from 1:52-5:52 PM CDT (1252 to 452 CST). The value of 125F was a May record, and rivaled all-time hourly records. Between the hours of 11:52 AM to 6:52 PM CDT (7 hours), heat indices were at least 111F. Ambient temperatures set daily and monthly records for May 9th. By proxy, it can be interpolated that at least southern inland Willacy County had similar heat index values, with slightly lower values farther north. There were no known direct fatalities, though hospitalizations for heat-related illnesses increased by an unknown number on this day.

An unseasonably strong sub-tropical ridge/heat dome centered over central and southern Mexico strengthened and shifted northward towards the Rio Grande Valley/Deep South Texas region. Temperatures at around 5,000 feet above the ground soared to 78 to 86 degrees Fahrenheit over the local area. This translated to surface temperatures rising into the upper 90s to mid 100s from May 7-9. Combined with dewpoint temperatures in the 70s to around 80, this produced apparent, or feels-like temperatures, between 111-116F across locations along and east of IH-69C/US 281 from Brooks/Hidalgo County into Cameron, Willacy, and Kenedy County. The hottest temperatures were located from the mid-lower Rio Grande Valley northward along I-69E and I-69C, peaking on May 9th.