Meteorological drivers of extreme swells on the Peruvian coast

In this study, we analyse a set of case studies to characterize the meteorological configurations associated with extreme ocean swells along the Peruvian coast, which are frequently produced by remote Pacific storms from both hemispheres. Using extreme-swell warnings from the Peruvian Navy and ERA5 reanalysis, we examine five austral-winter Southern Hemisphere (SH) events (very strong, south-westerly) and six boreal-winter Northern Hemisphere (NH) events (strong, north-westerly). Event-centred composites are computed over lead windows guided by estimated swell travel times (3–4 d in the SH; 8–11 d in the NH). In both hemispheres, these case studies show a deep extratropical cyclone exhibiting a vertically stacked structure throughout the troposphere before the coastal swell peak, while an upper-level jet core strengthens and organizes a persistent corridor of enhanced surface westerlies over the swell-generation region. In the SH, coherent surrounding ridging tightens the meridional pressure gradient and co-occurs with a strengthened, sharper polar-front jet. In the NH, preconditioning is dominated by a deep central–western North Pacific low with comparatively weak, localized ridging and a markedly intensified, more zonally extended subtropical jet, while the polar-front jet weakens. A flow-analogue analysis suggests that SH event-related surface winds have become more intense in recent decades, consistent with increased large-scale pressure contrasts and a shift toward more positive Southern Annular Mode conditions, whereas NH events show no robust signal, probably due to strong interannual-to-decadal variability. These results can support earlier recognition of remote swell hazards affecting Peru and, consequently, can lead to an improvement of early warning systems.