Grand Canyon National Park officials say three hikers have died in heat-related incidents in the inner canyon area, where temperatures can exceed 109°F (43°C) even in the shade during midday. Following the deaths, the U.S. National Weather Service issues an extreme heat watch for early next week, warning visitors of dangerous conditions during daytime hours. The watch is in effect from 10 a.m. local time Monday through 7 p.m. Tuesday. Forecasts indicate temperatures could reach or exceed 110°F, with some projections as high as 111°F, particularly in lower-elevation areas. PBS reports the expected heat at Phantom Ranch, a low-elevation location within the park. The warnings focus on the risk of heat-related illnesses without effective cooling and adequate hydration. While the specific circumstances of each death are not detailed in the provided coverage, all outlets link the recent fatalities to high heat in the inner canyon and emphasize that additional extreme heat is expected to persist into Monday and Tuesday.