The Rio Grande Valley is under a heat advisory, with humidity pushing feels-like temperatures into the triple digits.

The Valley is home to many oil field workers, construction workers and others who make a living outdoors. Experts say humidity can push people from heat exhaustion to heat stroke fast.

Early warning signs include headaches, nausea, dizziness, thirst and less frequent urination.

"Call 911 right away, but drink fluids, get some cold damp towels and put them under your armpits to start bringing your body temperature down," Emergency Management Coordinator Ricardo Salana of Hidalgo County said.

Officials are urging everyone to drink plenty of water and stay in the shade. People working on roadways should take periodic breaks.

Blacktop surfaces can run 10 degrees hotter than the surrounding air.