Synoptic climatology associated with heavy rainfall events in the Itajaí Valley region, Brazil

This study presents a synoptic climatology of heavy rainfall events (HRE) in the Itajaí Valley region (IVr) in the eastern Santa Catarina (SC) state between 2000 and 2022. A total of 195 HRE were identified, corresponding to accumulations greater than 27 mm per day. The mean synoptic pattern associated with HRE showed the presence of a cold front over the study region and a low-pressure system over northeastern Argentina and Paraguay that promoted warm advection over much of the SC state. This pattern was also observed at the 850 hPa level, where a cyclonic circulation centered over Paraguay two days before the HRE (day –2) intensified the moisture transport from the Amazon region over SC. On day 0, a trough in the middle and upper troposphere was observed over Argentina, Uruguay, and parts of southern Brazil, showing a typical mid-latitude dynamic system that reflects the cold front observed at the surface. The synoptic classification identified four main surface synoptic patterns associated with HRE in the IVr. The most frequent pattern was related to the presence of the South Atlantic Subtropical Anticyclone (SASA) with blocking characteristics. Two patterns were related to a typical cold front, and the last was associated with a cyclogenetic process. No correlation was found between the sea surface temperature (SST) and the occurrence of HRE in the IVr; however, the SST anomaly gradient observed around 35º S suggested that cold fronts may be anchoring over the region of anomalously cold waters over the coast of the south of Brazil.