Urban heat island intensity and spatial variability by synoptic weather type in the northeast U.S.

Understanding regional air temperature (T_a) variability and urban heat island (UHI) magnitude has posed challenges given the minimal observational stations in urban areas. This study uses a dense network to evaluate the degree to which synoptic weather influences the UHI intensity and fine scale T_a variability on days of extreme heat. We examine daytime and nighttime temperatures in four large northeastern cities (urban-suburban-rural) using a dataset with relatively high spatiotemporal resolutions (100–200 stations per area, 5 min or 60 min intervals) for May–Sept, 2006–2013. Results show stronger UHI intensity and enhanced T_a variability under hot, dry weather types, with the most intense UHIs overnight in dry conditions. Absolute T_a magnitudes within both urban and rural areas remain heightened under moist weather type conditions. New York City presents the highest average nighttime UHI intensity (3.51°C). Minimal, and at times negative, UHIs are often present in the daytime, appearing on 38% and 28% of days in New York City and Boston, respectively. An exploratory analysis demonstrates a significant ability to predict average T_a at each station using common environmental predictors. Findings emphasize the importance in distinguishing between absolute maximum T_a versus UHI intensity by weather type for communication and translation of heat mitigation practices and health protection by public health and urban planning agencies.