Impact of Storm Louis on two Spanish harbours: a multi-platform approach

Storm Louis struck southwestern Europe between 22 and 26 February 2024, producing severe metocean conditions that led to significant disruptions in transportation networks, widespread power outages, and one confirmed fatality. This high-impact event exemplified the growing threat that deep extratropical cyclones pose to European coastal infrastructure. The synoptic-scale characteristics of Storm Louis were examined using ERA5 reanalysis data, revealing a marked Azores High–Iceland Low pressure dipole configuration, indicative of the canonical manifestation of the positive phase of the North Atlantic Oscillation. A strong SW–NE pressure gradient gave rise to persistent and anomalously intense northwesterly maritime-polar winds over the northeastern Atlantic Ocean and the Iberian Peninsula that induced significant wave heights above 8 m. The concurrent impact on two geographically distant Spanish ports – Langosteira in the northwestern Iberian (NWI) region and Tarragona in the northeastern Iberian (NEI) region – was evaluated using a multi-platform observational framework that integrates in situ measurements from four moored buoys and two tide gauges with remotely sensed data provided by two high-frequency radar (HFR) systems. In the NWI (NEI) area, multiple observed wind and wave parameters associated with Storm Louis exceeded the 99.9th (99th) historical percentiles, based on the available 11-year observational record period spanning 2014–2024. Analysis of high-frequency sea level oscillations, recorded by tide gauges at both ports during Storm Louis, revealed contrasting wave-induced agitation responses between the Langosteira and Tarragona harbours, despite exceedance of their respective historical 99th percentile threshold. The former experienced a moderate but prolonged (33 h long) event peaking at 0.68 m with minimal storm surge influence, while the latter underwent a shorter (16 h long), more intense peak of 1.77 m, also decoupled from storm surge. Over the 2014–2024 period, the relationship between offshore wave parameters and inner-harbour agitation was explored to isolate the open-ocean conditions most strongly associated with critical in-port sea states likely to compromise maritime operations. Results revealed significantly high linear correlations between offshore wave height conditions and harbour agitation ( R = 0.88 for Langosteira, R = 0.75 for Tarragona). However, Tarragona harbour exhibited a more complex, bimodal directional response: peak agitation events were predominantly associated with moderate offshore wave heights (< 3 m) propagating from the southernmost sector, underscoring the harbour's marked sensitivity to wave incidence angle and its role in amplifying internal hydrodynamic response. Finally, HFR wave data, validated against buoy observations, reliably captured storm-induced waves, highlighting their value for real-time extreme-hazard assessment and climate-resilient port infrastructure.