GRAND CANYON NATIONAL PARK, Ariz. (AP) — Visitors to Grand Canyon National Park are being warned about extreme heat that will plague the popular destination early next week after a recent increase in heat-related incidents in the inner canyon, including the deaths of three hikers.

The U.S. National Weather Service issued an extreme heat watch at the Grand Canyon for midday Monday through Tuesday, forecasting temperatures that could reach or exceed 110 degrees Fahrenheit (43 degrees Celsius) at the low-elevation Phantom Ranch.

Hikers are "strongly advised" to avoid hiking in the middle of the day, the U.S. National Park Service said in a release this week following a "recent influx of heat-related incidents."

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An extreme heat watch was in effect on June 16 when two hikers, aged 67 and 68, were found dead on the North Kaibab Trail, which NPS describes as the most difficult of the major inner canyon trails. NPS said they appear to have succumbed to symptoms of heat-related illness.

A third person, 72, died June 12 along the South Kaibab Trail after becoming ill from the heat, NPS said.

About 90 miles (145 kilometers) south, Oak Creek Canyon visitors and residents were evacuated late Friday as a wildfire burned hundreds of acres just north of Sedona, Arizona.

Much of the western U.S. from the Rockies to the Pacific Coast were getting above-average temperatures Saturday and anticipating even hotter weather early next week. Officials also warned the prolonged dry, hot weather and relatively low humidity increased the risk of fire danger throughout the area.

Extreme heat increases risk of hiking at the Grand Canyon

Park and weather officials alike emphasize to Grand Canyon visitors that hiking conditions can be deceiving. Temperatures at the rim of the Grand Canyon are often 20 to 25 degrees F cooler than what hikers will experience at the bottom of the canyon.

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"It's just a hot place at the bottom of the Grand Canyon," said Justin Johndrow, a meteorologist with the National Weather Service office in Flagstaff, Arizona. Johndrow warned that the region is approaching the hottest period of the year before the rain during monsoon season later in the summer offers some relief from the heat.

Hikers may have cooler temperatures and an easier time going downhill to start the descending trails, but they face an intense climb of thousands of feet in elevation and much hotter bottom-of-the-canyon temperatures to get back up. Those conditions can cause heat illness symptoms to sneak up on visitors.

"That's very strenuous even on a mild day," Johndrow said of the hike back up to the rim. "Throw in temperatures of 105 to 110 degrees and that causes some pretty bad problems."

Park officials advised visitors to avoid strenuous hiking in the middle of the day.

Wildfire near Oak Creek Canyon posed risk to public safety

A federal interagency team and at least a dozen local agencies were working to combat the fire burning roughly 500 acres (202 hectares) of very steep and rough terrain near Oak Creek Canyon, said Dick Fleishman, fire information officer with the southwest area complex incident management team.

The fire is concentrated in the Red Rock-Secret Mountain wilderness area about seven miles north of Sedona, Arizona, but it has started to creep into the Coconino National Forest. Firefighters are working to contain the burn, prevent it from moving toward Oak Creek Canyon, where residents and visitors have been evacuated, or Sedona, and prepare for the possibility that it does.

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Fleishman said the steep slope where the fire is burning, the property at risk nearby, the heat firefighters are working in and the risk of post-fire flooding caused by rain rushing down the slope are among the reasons the Pocket Fire is particularly concerning.

"This fire ramped up in complexity quickly," he said. "We want to try and keep it as small a footprint as possible."

About 30 miles (48 kilometers) of the adjacent state highway was closed in both directions. Evacuations were issued for visitors and residents near Oak Creek Canyon, which attracts millions of visitors each year.

"For June 20," Fleishman said of his drive through the area, "I've never seen it that quiet."