The heatwave is expected to affect millions across Arizona and California, with elevated risks for heat exhaustion, heat stroke, and respiratory problems. Urban areas may face amplified dangers due to the urban heat island effect, which prevents cooling during nighttime hours. Vulnerable populations, including the elderly, children, and those with pre-existing health conditions, are particularly at risk. Air quality alerts in regions like Imperial Valley and Phoenix further compound health concerns, as high ozone levels can exacerbate respiratory issues. Residents are advised to take precautions to mitigate these risks.