Sea Breezes and New York City Heat Waves: Interactions, Effects, and Predictability

The interactions of sea breezes with land-enhanced warming and the urban heat island during heat waves are examined in the New York City area using hourly observational data over 1948-2014. A novel heat-wave definition incorporating both temperature and moisture is first used to identify 3-to-5-day heat waves and to closely track their spatial and temporal evolution. Sea breezes during these heat waves are then algorithmically identified and classified. The variations in strength, persistence, and orientation of sea breezes, interacting with local terrain and land-use type, are found to create differences in temperature and humidity at fine spatiotemporal scales. In particular, they are found to play an important role in creating mesoscale differences in near-surface temperature and moisture, local regimes which are divided sharply by the sea-breeze fronts — however, humidity and temperature variations across these fronts are shown to be largely compensatory, so that regional differences in equivalent temperature at any one time are typically minimal. Evidence is presented supporting the influence of coastline orientation and urban-heat-island circulation on sea breezes to explain the differences in the relationships between wind azimuth and net temperature & moisture advection among stations in New York City proper, and between them and a nearby inland region (northern New Jersey). Sea-breeze effects are shown to be more pronounced in early summer than late summer, hypothesized to be a consequence of seasonal coastal SST warming. Sea breezes are also shown to consistently vary depending on the strength and direction of the mid-tropospheric steering wind, in addition to mesoscale phenomena such as relative differences in temperature at a given hour. This relationship enables a first attempt at predictability of sea-breeze strength and timing based on synoptic-scale pressure anomalies, with encouraging results.