Atmospheric patterns favourable to storm surge events on the coast of Sao Paulo State, Brazil

Southeast Brazil is occasionally affected by intense storm surges that cause coastal erosion, coastal inundation, destruction of local infrastructure, and floods. This work is aimed at identifying the large-scale atmospheric conditions favourable to causing storm surges that reach the coast of the Sao Paulo State in Southeast Brazil. Based on ERA5 reanalysis data from May between 1981 and 2010, storms were identified on 89 surge days. Storm surge days are characterized by a significant wave height that exceeds 2.5 m. These surge days were clustered into three atmospheric patterns. Cluster Pattern 1 contains 10 storm surge days characterized by a low-pressure centre near the coastline and winds blowing parallel to the coast. These surface conditions are combined with upward vertical motion at 500 hPa and an upper-level jet stream, which helps rain formation over the ocean. Cluster Pattern 2 contains 22 events. The main feature of this pattern is the long and wide wind fetch area over the ocean, which generates a large area of intense winds that allows a more efficient propagation of high waves. This pattern shows the most significant rainfall values over the coastal area. Cluster Pattern 3 presents the largest number of surge days, totalling 57. The atmospheric pressure gradient established by the high-pressure system and the elongated trough over the ocean produces intense southerly winds along the coast, which favour high waves in this region. Therefore, the described atmospheric patterns favourable to storm surge events can be applied to forecasting systems and contribute to storm surge alerts in the Sao Paulo coastal zone.