Analysis of Hydrodynamic Processes That Caused Extreme Sea Levels and Flooding in Guadeloupe During Hurricane Maria (2017)

Hurricane-driven extreme sea levels and coastal flooding are major hazards for tropical islands, and understanding the meteorological and oceanic underlying processes is crucial as climate change might intensify these events. On 19 September 2017, Hurricane Maria passed 20 km south of Guadeloupe as a Category 4 on the Saffir–Simpson scale, generating offshore waves of up to 8 m and a maximum recorded still water level of 0.7 m above mean sea level, causing substantial flooding along the seafront. Before Maria, three pressure sensors were deployed in a reef–lagoon system southeast of Guadeloupe: two along a cross-shore transect (forereef slope and lagoon) and one on the backshore of a neighbouring bay. To examine the drivers of extreme sea levels and coastal flooding, data analysis was complemented by numerical modelling. At the regional scale, the phase-averaged SCHISM–WWM modelling system was implemented at the scale of the whole Guadeloupe Archipelago with a resolution reaching 10 m at the study site and reproduced short waves and mean water levels. Numerical experiments revealed that wave setup and atmospheric surge contributed almost equally, but flooding was not predicted, suggesting that additional processes may be missing. To evaluate this hypothesis, a local phase-resolving SWASH model was applied, revealing substantial infragravity (IG) waves (Hm0 = 0.3 m to 0.6 m) at the shoreline. For comparable mean water levels in the lagoon, SWASH predicted greater inundation, matching well available observations, highlighting the critical role of IG dynamics in coastal flooding assessments.