Long-term trends in heat wave gaps for the New York City metropolitan area

Heat waves occurring in close succession to one another are hazardous because of the prolonged stress on the human body and energy demand. A heat wave gap metric, the time between two adjacent heat wave events, was utilized to examine the gap length and frequency trend for several stations around New York City (NYC) during the last several decades. From 1961 to 1990 to 1991–2020, the average heat wave gap for the various stations decreased by 15–41 %, the number of short gaps (≤5 days) increased by 33–300 %, while the number of long gaps (>5 days) remained relatively constant. K-means, a clustering algorithm, applied to the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) daily reanalysis data was used to identify flow patterns associated with the short and long gaps. The leading short-gap pattern started with a weak cold front that ended the heat wave, while a highly amplified upper ridge over the central U.S. and a westward extension of a surface high pressure over the southeast U.S. advected warm air to the Northeast U.S. over the next few days to start another heat wave. The leading two long-gap patterns were associated with a stronger surface cold front, a weaker central U.S. upper ridge, and a deeper eastern U.S. upper trough.