The Latest: Grand Canyon hikes perilous during heat wave

PHOENIX (AP) — The Latest on the heat wave affecting most of Arizona and the Southwestern U.S. (all times local):

10:40 a.m.

The National Park Service is warning visitors to Arizona not to hike into the Grand Canyon because of excessive heat.

Temperatures below the rim of the canyon are expected to reach as high as 117 degrees this week. Temperatures on the rim are expected to be in the low to high 90s.

If hikers do decide to go ahead with their planned trips, the Park Service says they should take extra precautions to avoid being overcome by the excessive heat. That includes hiking only before 10 a.m. and after 4 p.m. to avoid strenuous exertion during the hottest part of the day. Drinking extra water and sports drinks will help prevent dehydration that can trigger a health crisis like a heat stroke.

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7:15 a.m.

American Airlines is warning passengers that it may have to ground flights in Phoenix during a heat wave that could send the temperature soaring to 120 degrees.

The airline is letting Phoenix passengers flying during the peak heat Monday through Wednesday to change flights without a fee. The forecast calls for a high of 118 on Monday and 120 on Tuesday in Phoenix.

The heat will have the biggest impact on smaller regional jets flying out of Phoenix.

Extreme heat creates changes in the air density that make it harder for airplanes to take off. Airlines respond by imposing weight restrictions, such as carrying less cargo and fuel. But in some cases, they will ground flights during the peak heat.