In this study, we propose an easy and robust algorithm to identify and track extratropical cyclone events using 850 hPa relative vorticity data, gaussian filter and connected-component labeling technique, which recognize the cyclone as areas under a threshold. Before selecting the events, the algorithm can include essential characteristics that are good metrics of intensity, like minimum mean sea level pressure and maximum 10-m winds. We implemented the algorithm in the Southern Hemisphere, using a 41-year high resolution dataset. Sensitivity tests were performed to determine the best parameters for detection and tracking, such as degree of smoothing, thresholds of relative vorticity at 850 hPa and the minimum area within the threshold. Two case studies were used to assess the positive and negative points of the methodology. The results showed that it is efficient in obtaining the position of extratropical cyclones in their most intense stage, but it does not always perform well during cyclolysis. We compare the methodology using 1-h temporal resolution to that using a 6-hours temporal resolution, and their reproducibility regarding the literature. The extratropical cyclone climatology in the Southern Hemisphere is provided and discussed. The algorithm developed here can be applied to datasets with good spacial and temporal resolution, providing a better inventory of extratropical cyclones.

Extratropical cyclones are the main drivers of high-energy wave events along the southern coast of Brazil, frequently producing hazardous coastal conditions. Between 2001 and 2020, we identified 51 high-impact coastal storms based on Marine Weather Warnings and ERA5 reanalysis. Events showed a clear seasonal pattern, with the highest occurrence in winter and autumn. Composite analyses revealed that these extreme events are consistently associated with strong meridional pressure gradients and southerly to southeasterly low-level winds, which establish long wind-fetch zones that favor the generation and shore-normal propagation of energetic waves. Significant wave heights typically exceeded 4 m along the entire coastline, with maxima south of 35° S. EOF analyses showed that the dominant mode of variability is a recurrent low-pressure system centered between 40 and 45° S over the southwestern Atlantic. In contrast, the second mode represents the dipole between continental high pressure and oceanic low pressure that intensifies storm-related wave generation. Case studies from 2008 and 2015 confirmed that these synoptic patterns result in prolonged hazardous sea states and coastal impacts, including bar closures at the Port of Rio Grande, totaling 355 h of inoperability. These findings provide a clear characterization of the meteoceanographic patterns associated with high-impact coastal storms in southern Brazil and offer a climatological basis for improving early warning, navigation safety, and coastal risk management.

The Earth’s weather and climate are strongly influenced by synoptic-scale systems such as extratropical cyclones. From this point of view, extratropical cyclones are very important for Equator–Pole heat exchange, and their positions are relevant to the understanding of the behavior of this system under current conditions and in the context of climate change. Baroclinic instability (BI), meridional heat flux (MHF), and kinetic energy (KE) are among the ways of calculating storm tracks (the regions in which extratropical cyclones most often occur). Forecasting is important for predicting the evolution of these phenomena and preparing future political decisions. In this study, we used ERA5 reanalysis data and BESM model forecasts to calculate BI, MHF, and KE. Overestimation of the BESM BI at lower and higher latitudes and underestimation of BI at medium latitudes were observed. In general, KE and MHF were underestimated and were displaced southward in the BESM. The analyses show a tendency towards poleward displacement of these tracks for all variables studied in in this paper. The scenarios show the same bias, with RCP8.5 having more extreme changes in all situations.

O Litoral Sul do Brasil encontra-se em uma região em que ocorrem a passagem de ciclones extratropicais e de sistemas frontais que influenciam as condições de mar, através da formação de ressacas, causando impactos na costa, principalmente na atividade portuária, nos tripulantes, nas embarcações e na população que habita as regiões costeiras. Diante do exposto, o objetivo deste trabalho foi de realizar um estudo dos eventos de ressaca no Litoral do Rio Grande do Sul e de Santa Catarina e a variabilidade associada ao Fenômeno El Niño-Oscilação Sul (ENOS), a partir de Avisos de Mau Tempo da Marina do Brasil e dados de reanálise ERA5. Os resultados mostram que as ressacas ocorrem em qualquer época do ano, mas com maior frequência durante o outono e o inverno. Os padrões associados no outono e inverno, indicam a presença de um maior gradiente de pressão atmosférica na área de estudo, favorecendo ao predomínio de ventos do quadrante sul e o consequente empilhamento de água na costa. Por fim, através do cálculo da instabilidade baroclínica, foi possível observar que as ressacas ocorridas durante as fases neutra e positiva do fenômeno ENOS estão associadas a passagem de ciclones extratropicais e sistemas frontais mais intensos, quando comparados com períodos de La Niña.

Extratropical cyclones are the main drivers of high-energy wave events along the southern coast of Brazil, frequently generating coastal storms and hazardous conditions. This study analyzes the occurrence and characteristics of extreme wave events between 2001 and 2020 along the coastal zone from Arroio Chuí to Cabo de Santa Marta, based on warnings of sea state hazards issued by the Brazilian Navy Hydrographic Center. Events were selected using the 95th percentile of significant wave height, considering only episodes with waves exceeding 4.0 m reaching the coast. To avoid double-counting, consecutive warnings within two days were grouped as a single event. Reanalysis data from ERA5 were used to describe the associated atmospheric and oceanographic patterns. A total of 51 high-impact coastal storm events were identified, with seasonal distribution showing higher frequency during winter (19 cases) and autumn (15 cases). Out of these events, 25 were associated with adverse navigation conditions at the coastal bar, accounting for 355 hours of impracticability. Results highlight the dominant role of strong winds and frontal systems in generating extreme sea states and their socio-economic impacts. The study provides a climatological baseline for the region and contributes to improving forecasts and risk management strategies under changing climate conditions.

Extratropical cyclones are key features that contribute to changes in precipitation, wind, and temperature at midlatitudes, sometimes causing extreme conditions. Despite the southwest Atlantic Ocean being recognized for cyclone formation and intensification, several aspects of spatial and temporal variability remain unclear. Hence, in this study, the overall characteristics of cyclones that form within the southwest Atlantic Ocean are investigated. We also analyze the interannual variability in the frequency of cyclone occurrences across each season. To accomplish this, we use a dataset from the hourly fifth generation of global climate reanalysis from the European Centre for Medium Range Weather Forecasts (ERA5/ECMWF) spanning 41 years. The results revealed increased interannual variability, which fit with a cubic regression for the entire study area, as well as for the northern and southern parts of the area, divided by the 35°S latitude. Seasonally, we found a positive trend of 1.7 per decade in cyclone occurrence for the southern part of the area during summer, with a statistical significance of 95%. The Fourier analysis revealed an energy peak at 2–3 years in the northern part during winter, as well as in the entire area during spring, summer, and autumn. Additionally, important peaks at the 5‐year, 6‐year, and 8–10‐year periods were observed. Moreover, we investigated extreme events and found that those selected by the minimum sea level pressure are more concentrated south of intense events by 10‐m winds. The composites of meteorological fields during intense cyclones that formed near the coastal area suggest that the equatorial entrance of the upper‐level jet stream is a preferential condition for the development of intense events. In addition, our analysis revealed the importance of a wide‐ranging meridional moving trough in the upper and middle level troposphere and the relevance of moisture transport via the northwest low‐level jet from the tropics to the coastal area, which induces intense cyclones in the southwestern Atlantic region.