From Kim Stanley Robinson’s great book The Ministry for the Future:

“a wet-bulb temperature of 35 [95 degrees Fahrenheit] will kill humans, even if unclothed and sitting in the shade; the combination of heat and humidity prevents sweating from dissipating heat, and death by hyperthermia soon results.”

The south Texas borderlands will once again be perilously close to a wet bulb temperature of 95 degrees Fahrenheit tomorrow afternoon. It’ll be 92 in Laredo and McAllen. This will take a severe toll on the area’s migrant population.

National Weather Service map of the entire U.S.-Mexico border showing wet bulb temperatures at 4PM Eastern time tomorrow, July 10.

Areas shown as "extreme" include

Yuma, AZ (wet bulb 89), and nearly everything from Eagle Pass to Brownsville (at least 90, hitting 92 in Laredo and McAllen, and 93 just north of Laredo along I-35).

This map comes from the National Weather Service.