CoAuthors

Gustavo Goni (NOAA / AOML, USA); Molly Baringer (NOAA / AOML, USA); Denis Volkov (UM / CIMAS | NOAA / AOML, USA)

Extensive low-lying areas along the east coast of United States are currently affected by recurrent tidal flooding events that have been increasing in frequency and magnitude. These events pose threat for coastal communities and infrastructure and requires efforts to mitigate potential damage and improve resilience. The dynamics associated with the intense Florida Current flow across the Florida Straits sustains a sea-level difference of over 1m between the eastern United States coast, and the Bahamas. Changes in the Florida Current dynamics can, therefore, drive relevant sea-level variability at both sides of the Florida Straits at various time-scales, with a decrease (increase) in transport being associated with an increase (decrease) in coastal sea level along the U.S. coast. In this presentation, data from satellite altimetry, tide gauges, hydrographic surveys and cable-derived transports reveals that changes in the Florida Current transport and temperature provide important sources of coastal sea level variability along the east coast of the United States. On seasonal time-scales, analysis reveals that westward propagating sea-height anomaly signals originated in the east North Atlantic Ocean can affect the Florida Current transport, leading to sea-level changes that can be as large as 20 cm on both sides of the Florida Straits. On interannual time-scales, analysis of the satellite altimetry record and sea level data derived from tide gauges along the east coast of the United States shows that during 2010-2015 sea level increased south of Cape Hatteras at rates exceeding 25 mm per year (approximately 5 times the global average of ~5 mm per year for the same period). Analysis of a comprehensive set of ocean observations including XBT transects, and hydrographic surveys across the Florida Straits has revealed substantial warming of waters carried by the Florida Current during this period. The entire water column in the Florida Straits shifted from a regime of negative temperature anomalies during 2010-2013 to one of positive temperature anomalies during 2014-2017. It is found that during 2010-2015 warming of the Florida Current accounts for a thermosteric sea level increase of 19 mm per year, which explains most of the sea level trend observed by satellite altimetry and tide gauges south of Cape Hatteras, where the Gulf Stream detaches from the coast.