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A dangerous heat wave is expected to hit the West Coast over the holiday weekend.

Forty-three million people across much of California, southern Nevada and western Arizona are already under an excessive heat watch, and that number is expected to rise.

Forecasters warn that this heat wave has the potential to break all-time high temperature records for the region. National Weather Service Los Angeles suggested that “all daytime outdoor activities should be limited or canceled.”

Excessive heat watches are expected to start on Friday for valleys and mountains and Saturday for coastal areas.

Sunday is expected to be the hottest day, with temperatures as high as 115 degrees are expected away from beaches, according to the National Weather Service.

Close to 100 record high minimum temperatures are expected to be broken during the same time frame.

Overnight lows are expected to be warm in the 70s and 80s, which will allow for little relief for the region. Warm overnight temperatures impact people the most during heat waves as the warm weather does not allow buildings and people to cool down overnight.

This weekend is expected to be worse than the region’s recent August heat wave, which prompted rolling blackouts in the area.

The National Weather Service warned that “extreme stress on our power infrastructure may lead to power outages.” There is also a high risk of heat-related illnesses.