Heat Endures in the Southwest as the Monsoon Season Lags

Many Texans are familiar with the chorus of cicadas that fills the air on the hottest days of early July. But this week, the bugs seem particularly raucous.

It could be, at least in part, a result of the heat wave that has been baking the region and shows no signs of letting up. On Tuesday, the high temperature was expected to reach around 103 degrees in El Paso and San Antonio.

It’s not that individual cicadas are louder than they were before, said Allen F. Sanborn, an emeritus professor of biology at Barry University in Miami who retired to central Texas. Instead, Dr. Sanborn has noticed, the insects seem to be active for more hours in the day.

“They start calling earlier because the minimum air temperature combined with solar radiation is reached earlier in the day,” he said. “They also call later into the afternoon and evening because they can maintain the elevated body temperatures for a longer period of time.”

While the cicadas are singing, tens of thousands of people are sweltering. A heat dome of high pressure that has parked over New Mexico and West Texas, and the soaring temperatures across much of the South, from Florida to California, are expected to last at least two more weeks. Experts estimate that more than 50 million people across the United States live in areas expected to have dangerous levels of heat.

Around this time of the year, residents of New Mexico and Arizona can typically expect some respite in the form of the monsoon season, which brings heavy thunderstorms that cool the air on otherwise scorching days.

But this year, those storms are running behind schedule.

When they first arrive, the monsoons can make the heat even more dangerous — at least momentarily — by adding humidity to the equation, said Michael Crimmins, a professor of environmental science at the University of Arizona in Tucson. He said that research was still being done to determine how climate change affected the monsoon season, and he added that the lack of storm clouds over southern Arizona had “the fingerprints of El Niño,” a cyclical weather pattern.

For people without shelter, the relentless heat is particularly dangerous.

Bob Feinman, the vice chair of Humane Borders, a nonprofit organization in Tucson, said that migrants walking through the Arizona desert from the Mexico border had been in dire need of water during the heat wave. Lately, the water tanks that the organization has placed in high-traffic areas have had to be refilled more frequently.

“More water is being used, and more stations have been needed in areas like Sonoita, just north of the border with Mexico,” he said.

Thunderstorms were likely to bring some rain to Sonoita on Tuesday, and possibly to Tucson as well, but the sun was expected to keep shining elsewhere.

The high temperature was expected to approach 109 degrees in Phoenix and 105 in Tucson, and similar triple-digit temperatures were likely to continue for at least a week, possibly approaching record-breaking levels by the weekend.

John Washington and Sheryl Kornman contributed reporting.