The Relationship Between Coastal Precipitation along Southeastern Brazil and Offshore Low-pressure Systems

Heavy precipitation significantly impacts society, triggering disasters such as floods and landslides. This study examines the meteorological factors influencing heavy precipitation events in Southeastern Brazil, with a focus on the role of offshore low-pressure systems and associated changes in low-level moisture transport. Our methodology involved identifying common patterns of heavy precipitation, defining heavy precipitation days, distinguishing cases with and without offshore low-pressure systems, and analyzing their relationship with anomalous potential vorticity. Results show that offshore low-pressure systems induce a reversal of the prevailing moisture flow -- from the typical seaward continental outflow to onshore transport from the Atlantic Ocean -- during heavy precipitation days. This reversal enhances moisture convergence and rainfall near Southeastern Brazil. Furthermore, offshore low-pressure systems enhance precipitation in summer and fall, whereas spring precipitation remains largely unaffected by their presence. Analysis of offshore low-pressure system formation shows that potential vorticity breaking, particularly potential vorticity cutoffs, is a more convincing factor than jet seasonality, with a high frequency of events near Southeastern Brazil in summer. These findings improve our understanding of the dynamics leading to heavy precipitation in the region and provide a foundation for future research on offshore low-pressure system formation mechanisms.