A significant heatwave is set to impact the midwest and northeast United States starting Monday, with dangerously high temperatures expected to persist throughout the week. The National Weather Service has issued excessive heat watches for areas including Michigan, Ohio, western Pennsylvania, and Northeast Indiana, predicting heat index values of 100°F (38°C) or higher. Cities like Detroit and Phoenix are expected to experience record high temperatures, with Detroit facing its worst heatwave in 20 years. Residents are advised to stay hydrated, avoid sun exposure, and use air-conditioned spaces. Officials in states like Ohio and Georgia are opening cooling centers to help residents cope with the heat. The heatwave poses serious health risks, including heat cramps, heat exhaustion, and heat stroke, making it crucial for individuals to monitor their health and check on vulnerable neighbors.