The system’s length and strength will be compounded by some offshore winds, which will help keep any marine influence at bay and keep temperatures high, even overnight.

The most intense heat of the summer arrives this week when parts of Los Angeles will be under extreme heat warnings and other areas will face severe fire conditions. What authorities described as a severe heat event with days of temperatures in the upper 90s and well into the 100s will begin Wednesday and continue through the weekend.

Thousands of utility customers in and around Los Angeles were without power Thursday morning as a heat wave continued to bake Southern California.

Starting Wednesday, temperatures are expected to be in the high 90s and low 100s in inland areas. Officials say now is the time to prepare.

The report, released this week, found that 58% of fast-food workers surveyed in July said they had worked in excessive heat conditions in the last year. And nearly half, or 48%, reported experiencing heat illness symptoms including headaches, fatigue, dizziness, confusion, muscle pain or nausea.

A dangerous heat wave descended on much of California and the U.S. Southwest, with triple-digit temperatures expected along with a higher risk of wildfires.