Coastal Floods and the Lingering Effects of the Shelfbreak Jet - A case study of how local ocean currents contribute to coastal flooding in Southern New England (US)

In March of 2018, a winter storm hit Southern New England (US East Coast), with most of the coastal cities experiencing minor to moderate coastal floods. However, days after the storm passed and the winds and waves calmed down, the tide-gauge data continued to reach minor flooding levels. What was the cause of this prolonged recurrent flooding? Here we argue that the lingering effects of local ocean current dynamics contributed to this flooding.Along the US East Coast, an important driver of coastal sea-level variability is ocean dynamics, related to both large-scale circulation, such as the Gulf Stream, but also smaller local ocean currents. A relevant circulation feature in Southern New England is the Shelfbreak jet (SBJ). The SBJ flows equatorward from the Labrador Sea towards the Gulf Stream at Cape Hatteras following the shelf break along the Northeast US coast. In a recent study, we showed that the SBJ and sea level along the southern New England coast are highly correlated, especially at timescales of 1-15 days (Camargo et al., 2024). ​​Since this frequency band coincides with the timescales of storm surges, we explore the implication of our findings for coastal flooding. We find that the SBJ explains, on average, about 25% of the storm surge variance for flood days along Southern New England. Specifically, for the March 2018 winter storm, SBJ dynamics are responsible for more than 90% of the storm surge observed 4 days after the peak of the storm. That is, there would have been no flooding so many days after the storm passed if not for SBJ-related-dynamics.Our results suggest local ocean dynamics are an important component of storm surges in Southern New England, and contribute to lingering flooding after a storm has passed. Thus, we advocate that ocean dynamics should be considered in flood studies elsewhere. Furthermore, our results suggest that focusing only on large-scale circulation, such as the Gulf Stream or ocean overturning, may not be satisfactory for understanding the most basic dynamics essential for making meaningful projections of the future.Reference: Camargo, C. M. L., Piecuch, C. G., & Raubenheimer, B. (2024). From Shelfbreak to Shoreline: Coastal sea level and local ocean dynamics in the northwest Atlantic. Geophysical Research Letters, 51, e2024GL109583. https://doi.org/10.1029/2024GL109583

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