Synoptic climatology of nuisance flooding along the Atlantic and Gulf of Mexico coasts, USA

Nuisance flooding (NF; also known as high-tide, or “sunny day” flooding) is an increasingly prevalent phenomenon afflicting coastal developments worldwide. NF often results when high tides, exacerbated by global sea level rise, coincide with onshore-directed surface winds. The elevated tidal condition, compounded by frictionally forced ocean currents, then inundates coastal infrastructure, posing a non-life-threatening inconvenience for local residents. Even though NF events are formed by a coupling of atmospheric and oceanic conditions, the large-scale atmospheric circulations favorable for NF have received little attention. Using a 40 year NF database derived from coastal gauge data, this study identifies the mid-tropospheric synoptic atmospheric patterns within days of NF events along the Atlantic and Gulf of Mexico coasts of the USA. ERA-Interim reanalysis supplies 500 hPa geopotential height patterns over North America that coincide with NF events. Subsequently, a principal components analysis is performed upon all NF-associated 500 hPa patterns, disaggregated by region (New England, Mid-Atlantic, and Gulf Coast), to identify dominant intra-variability NF-related circulations. Consistent with prior work, results show that NF frequency is increasing with time. Further, each region is characterized by a unique set of dominant NF synoptic patterns. Most patterns have clear physical associations to NF mechanisms, such as a nearby 500 hPa trough that would support a surface cyclone and strong onshore surface winds, or a mid-level high-pressure cell that would direct onshore-oriented return flow along its western periphery. However, some patterns correspond less obviously to oft-referenced NF mechanisms and may instead reflect low-frequency modes of variability and/or localized influences.