Extreme waves generated by cyclonic winds in the western portion of the South Atlantic Ocean

This article analyzes the spatial distribution of extreme waves generated by extratropical cyclones and studies the atmospheric conditions that lead to the most severe events in the Southwestern portion of the South Atlantic Ocean. Significant wave heights from the NCEP/WW3 hindcast and atmospheric fields from NCEP/CFSR are selected for the analysis that joins automatic tracking of the storms with visual analyses of the most relevant cases. The synoptic pattern of extreme events suggested that extreme waves can occur in three regions of the cyclones: (1) behind the cold front; (2) along the warm front; and (3) ahead of the cold front. The first pattern is widely reported in the literature, while the others are unexplored in the region and are first reported in this paper. It was also shown that the anticyclone position relative to the cyclone center plays an important role in the extreme waves in two ways: (1) due to the increase of horizontal pressure gradient and, consequently, surface wind speed; and (2) affecting the cyclone displacement speed, which determines the fetch positioning and the wave generation process. The novel features identified show that slow cyclones tend to promote longer events of extreme waves, with impact on larger areas. •The spatial distribution of extreme waves and the atmospheric conditions that lead to the most severe events are studied.•Hs from the NCEP/WAVEWATCH-III hindcast and atmospheric fields from NCEP/CFSR for the South Atlantic are selected.•Independent events of extreme waves are constructed by picking one value of Hs per event at each grid point.•Cyclones are identified and tracked based on relative vorticity at 850 hPa computed from the winds.•Extreme waves occurred in regions: (1) behind the cold front, (2) along the warm front; and (3) ahead of the cold front.