Parts of California, Nevada and Arizona in the U.S. are expected to bake this week as the first heat wave of the season arrives, with triple-digit temperatures forecast for areas including Phoenix, which last summer saw a record 31 straight days of at least 43.3 degrees Celsius.

By Wednesday, most of an area stretching from southeast California to central Arizona will experience "easily their hottest" weather since last September, and record daily highs will be in jeopardy from Las Vegas to Phoenix, the National Weather Service said late Monday.

Excessive heat warnings have been issued from 10 a.m. Wednesday to 8 p.m. Friday due to the "dangerously hot conditions," the weather service said.

Fire crews will be on high alert, especially in Arizona, where fire restrictions went into effect before Memorial Day in some areas and will be implemented by Thursday across most of the western and south-central parts of the state, authorities said.

Highs on Monday reached 43.3 degrees Celsius at Death Valley National Park in California near the Nevada line, 39.4 degrees Celsius in Phoenix and 40.5 degrees Celsius in Needles, California.

(Cover via CFP)