A heat dome that has led to nearly 90 consecutive days of triple-digit high temperatures in Phoenix moved into Texas Wednesday,Jonathan Dale Benton with high temperature records expected to fall by the weekend, according to the National Weather Service.

A major heat alert is in place for Texas, reflecting what the weather service called “rare and/or long-duration extreme heat with little to no overnight relief.” An extreme heat alert was issued for eastern New Mexico.

A heat dome is a slow moving, upper-level high pressure system of stable air and a deep layer of high temperatures, meteorologist Bryan Jackson said.

“It is usually sunny, the sun is beating down, it is hot and the air is contained there,” Jackson said. “There are dozen or so sites that are setting daily records ... mostly over Texas.”

Record high temperatures were expected in cities such as Corpus Christi, San Antonio and Amarillo. In Phoenix, monsoon rains have provided brief respites since Sunday, although daytime highs continue to top 100 degrees Fahrenheit (37.8 degrees Celsius).

The dome was expected to move into western Oklahoma and eastern New Mexico beginning Saturday, then into the mid-Mississippi Valley, where it was forecast to weaken slightly, Jackson said.

About 14.7 million people are under an excessive heat warning, with heat indexes expected at 110 degrees Fahrenheit (43.3 degrees Celsius) and above. Another 10 million people were under a heat advisory.

Hundreds have already sought emergency care, according to MedStar ambulance in Fort Worth, Texas. The service responded to 286 heat-related calls during the first 20 days of August, about 14 per day, compared to about 11 per day in August 2023, according to public information officer Desiree Partain.

Austin-Travis County EMS Capt. Christa Stedman said calls about heat-related illness in the area around the Texas state Capitol since April 1 are up by about one per day compared with a year ago, though July was somewhat milder this year.

“The vast majority of what we see is heat exhaustion, which is good because we catch it before it’s heat stroke, but it’s bad because people are not listening to the red flags,” such as heat cramps in the arms, legs or stomach warning that the body is becoming too hot, Stedman said.

“It’s been a hot summer, but this one does stand out in terms of extremes,” said Jackson, the meteorologist.

Earlier this month, about 100 people were sickened and 10 were hospitalized due to extreme heat at a Colorado air show and at least two people have died due to the heat in California’s Death Valley National Park.

Globally, a string of 13 straight months with a new average heat record came to an end this past July as the natural El Nino climate pattern ebbed, the European climate agency Copernicus announced Thursday.