Man, it's a hot one: Trends and extremes in Florida autumn heat stress

Abstract Extreme heat is the deadliest weather‐related hazard in the United States, and is increasing in frequency, intensity and duration due to climate change. Heat stress is broadly defined as environmental influences on body temperature, and in this study is evaluated using wet bulb globe temperature (WBGT), which incorporates temperature, humidity, wind speed and solar radiation. Heat stress and associated humid heat have increased significantly across many regions of the globe, particularly in the subtropics and Tropics, which exacerbates health and excess mortality risks in those areas. However, heat stress has typically been investigated as a solely summer phenomenon. This study uses WBGT to examine heat stress trends and extremes during climatological autumn from the 1950s to 2022 at eight Florida cities. Results show that average autumn heat stress has increased significantly throughout much of Florida, particularly at coastal locations in the Florida Peninsula. Daytime heat stress increases were larger than their night‐time counterparts in northern Florida, while the opposite was true in central and southern Florida. Extreme (90th percentile) autumn heat stress events also increased in intensity and frequency, particularly in the Florida Peninsula and Florida Keys. Furthermore, locations in the Florida Peninsula and Florida Keys experienced increases of greater than 1.5 extreme autumn heat stress days per decade. Heat stress trends were predominantly largest in urban coastal environments, suggesting links to urbanization as well as statistically significant early autumn warming trends in sea surface temperatures. Overall, results indicated that heat stress in Florida is no longer solely a summer hazard and poses a particular threat to coastal areas in early autumn when ocean heat content is still near its climatological peak.