PHOENIX — American Airlines has cancelled 38 flights in and out of Phoenix on Tuesday afternoon because of extreme heat.

The cancellations are for operations by smaller regional jets that have lower maximum operating temperatures than full-size airliners. Those jets can’t operate when it’s 118 degrees or above.

American warned passengers over the weekend that it may have to ground flights during a heat wave that could send the temperature soaring to near 120 degrees. Spokesman Ross Feinstein says the late afternoons are the peak affected times.

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 119 Tuesday.

Extreme heat creates changes in air density that makes it harder for airplanes to take off.

Sizzle on the Strip

Tourists hitting the Las Vegas Strip will feel the sizzle Monday as temperatures could top 114 degrees.

Meteorologist Ashley Allen with The National Weather Service in Las Vegas says the city’s airport is forecast to hit 114 on Monday, but temperatures on the Strip could reach somewhere between 115 and 120 degrees.

Allen says the Las Vegas Strip’s tall, close buildings and long stretches of concrete cause the area to heat quickly and cool slowly. She says it’s hard to predict exactly how hot the Strip will get because the Weather Service does not get official readings there.

The Las Vegas-area is forecast on Tuesday to tie a record high of 117 degrees, last recorded in 2013.

An excessive heat warning is in effect as temperatures are expected to stay above 110 degrees into the weekend.

National Park Service issues warning

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.