The heat index, used by forecasters to warn persons what warm weather will feel like, regularly under-estimates how hot heat waves feel, according to an analysis by climate scientists at the University of California, Berkeley.
When taking into account humidity, the actual heat felt is sometimes more than 20 degrees Fahrenheit hotter.
A higher heat index means that the human body is more stressed during heat waves than public health officials may realize, the researchers say. You can read more about the study at https://www.preventionweb.net/news/todays-heat-waves-feel-lot-hotter-heat-index-implies