NOAA's National Weather Service (NWS) currently issues a suite of excessive heat products to provide the Nation advance notice of excessive heat events for the protection of life and property. Today, these products are issued based on a single heat index value derived from temperature and humidity. A national Heat/Health Warning System (HHWS) based upon empirical data would provide the NWS with tailored excessive heat guidance related to actual mortality and improve our forecast and warnings of excessive heat events.

The NWS is developing a plan to expand the number of HHWS from the current 14 cities to each U.S. municipality with population exceeding 500,000. In all, greater than 70 U.S. cities meet the criteria. This paper will describe the implementation process and benefits of a national HHWS by the NWS.