Pablo Lorente

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.

Coastal upwelling has been extensively studied since it plays a critical role in the connectivity between offshore waters and coastal ecosystems, which has impacts on water quality, fisheries, and aquaculture production. Significant efforts have been devoted to the quantification of the intensity, duration, and variability of this phenomenon by means of coastal upwelling indexes (CUIs), derived from wind, sea level pressure, or sea surface temperature data. Although valuable, first-order descriptors, such classical indexes have been reported to present some limitations. As one of the major shortcomings is the omission of the direct influence of ocean circulation, this work introduces a novel CUI, generated from remotely sensed hourly surface current observations provided by a high-frequency radar (HFR). The consistency of the proposed index (CUI-HFR) is assessed in two different oceanographic areas during two distinct time periods: in the north-western Iberian (NWI) peninsula for 2021 and in the Bay of Biscay (BOB) for 2014. To this aim, CUI-HFR is compared against a traditional CUI based on hourly wind observations (CUI-WIND) provided by two buoys. Likewise, the skill of CUI-HFR to identify upwelling and downwelling processes is also qualitatively evaluated. Complementarily, the prognostic capabilities of the GLOBAL analysis and forecasting system to accurately reproduce upwelling and downwelling events in the NWI area are also analysed (CUI-GLOBAL). Results obtained in these two pilot areas revealed the following: (i) noticeable agreement between CUI-HFR and CUI-WIND, with correlation coefficients above 0.67; and (ii) a proven ability of CUI-HFR and CUI-GLOBAL to categorize a variety of upwelling and downwelling episodes, which highlights their potential applicability for direct upwelling monitoring over any coastal area of the global ocean.

A long-term multi-parameter skill assessment of a 5-MHz Coastal Ocean Dynamics Applications Radar (CODAR) SeaSonde High-Frequency radar (HFR) network deployed along the Galician Coast (NW Iberian Peninsula) was attempted for 2014–2016. To this aim, wave estimations from two HFR sites, obtained directly by the CODAR radar proprietary software, were independently validated against hourly in situ observations from two moored buoys for two different periods. The accuracy assessment of significant wave height (H_s) revealed a consistent agreement with Pearson´s correlation coefficients (r) above 0.75 and normalized root mean squared errors below 0.4. An overall slight overestimation of H_s radar estimations was evidenced, likely due to spurious contributions to the directional spectra. The seasonal analysis revealed that the performance of this low mono-frequency radar was more precise for high-sea states during wintertime, whereas the quality and availability of radar data decreased under summer less energetic conditions, in accordance with previous works. In the case of the centroid wave period, HFR performance was consistent through the different years, with r values emerging in the range of 0.61–0.74. The directional accuracy was moderately good, with NW and W-NW as predominant sectors. Despite r values above 0.74, a tendency for CODAR HFR-derived incoming mean wave direction to be aligned more perpendicular to the coast compared to offshore in situ data was also observed. Furthermore, the relationship between the North Atlantic Oscillation (NAO) and HFR wave estimations was explored. A subtle but statistically significant connection was found, with H_s and centroid wave period being positively correlated with NAO daily index. Complementarily, the skill of the Galician HFR system was evaluated under positive and negative NAO conditions in order to elucidate whether the radar accuracy is or is not NAO-phase dependent. No substantial differences could be found for each of the three parameters analysed as HFR accuracy remained mostly unaffected by swings in the NAO index. Finally, it can be concluded that properly treated CODAR radar-derived wave estimations can be potentially employed for operational coastal monitoring across a wide range of sea states.

In this work, a multi-parameter inter-comparison of diverse ocean forecast models was conducted at the sea surface, ranging from global to local scales in a two-phase strategy. Firstly, a comparison of CMEMS-GLOBAL and the nested CMEMS-IBI regional system was performed against satellite-derived and in situ observations. Results highlighted the overall benefits of both the GLOBAL data assimilation in open-waters and the increased horizontal resolution of IBI in coastal areas, respectively. Besides, IBI proved to capture shelf dynamics by better representing the horizontal extent and strength of a river freshwater plume, according to the results derived from the validation against in situ observations from a buoy moored in NW Spain. Secondly, a multi-model inter-comparison exercise for 2017 was performed in the Strait of Gibraltar among GLOBAL, IBI and the nested SAMPA high-resolution coastal forecast system in order to elucidate the accuracy of each system to characterize the Atlantic Jet (AJ) inflow dynamic. A quantitative validation against High Frequency radar (HFR) hourly currents highlighted both the steady improvement in AJ representation in terms of speed and direction when zooming from global to coastal scales though a multi-nesting model approach and also the relevance of a variety of factors at local scale such as a refined horizontal resolution, a tailored bathymetry and a higher spatio-temporal resolution of the atmospheric forcing. The ability of each model to reproduce a 2-day quasi-permanent full reversal of the AJ surface inflow was examined in terms of wind-induced circulation patterns. SAMPA appeared to better reproduce the reversal events detected with HFR estimations, demonstrating the potential added value of coastal models with respect to coarser parent regional systems. Finally, SAMPA coastal model outputs were also qualitatively analysed in the Western Alboran Sea to put in a broader perspective the context of the onset, development and end of such flow reversal episodes.

The present work focuses on the long-term coastal monitoring of the Atlantic surface inflow into the Mediterranean basin through the Strait of Gibraltar. Hourly current maps provided during 2016–2017 by a High Frequency radar (HFR) system were used to characterize the Atlantic Jet (AJ) since changes in its speed and direction modulate the upper-layer circulation of the Western Alboran Gyre (WAG). The AJ pattern was observed to follow a marked seasonal cycle. A stronger AJ flowed north-eastwards during autumn and winter, while a weaker AJ was directed more southwardly during the middle of the year, reaching a minimum of intensity during summertime. A strong relationship between AJ speeds and angles was evidenced: the AJ appeared to be frequently locked at an angle around 63°, measured clockwise from the North. The AJ speed usually fluctuated between 50 cm·s⁻¹ and 170 cm·s⁻¹, with occasional drops below 50 cm·s⁻¹ which were coincident with abrupt modifications in AJ orientation. Peaks of current speed clearly reached values up to 250 cm·s⁻¹, regardless of the season. A number of persistent full reversal episodes of the surface inflow were analyzed in terms of triggering synoptic conditions and the related wind-driven circulation patterns. High sea level pressures and intense (above 10 m·s⁻¹), permanent and spatially-uniform easterlies prevailed over the study domain during the AJ collapse events analyzed. By contrast, tides seemed to play a secondary role by partially speeding up or slowing down the westward currents, depending on the phase of the tide. A detailed characterization of this unusual phenomenon in the Strait of Gibraltar is relevant from diverse aspects, encompassing search and rescue operations, the management of accidental marine pollution episodes or efficient ship routing.

The Galician coast (NW Spain) is a region that is strongly influenced by the presence of low pressure systems in the mid-Atlantic Ocean and the periodic passage of storms that give rise to severe sea states. Since its wave climate is one of the most energetic in Europe, the objectives of this paper were twofold. The first objective was to characterize the most extreme wave height events in Galicia over the wintertime of a two-year period (2015–2016) by using reliable high-frequency radar wave parameters in concert with predictions from a regional wave (WAV) forecasting system running operationally in the Iberia-Biscay-Ireland (IBI) area, denominatedIBI-WAV. The second objective was to showcase the application of satellite wave altimetry (in particular, remote-sensed three-hourly wave height estimations) for the daily skill assessment of the IBI-WAV model product. Special attention was focused on monitoring Ophelia—one of the major hurricanes on record in the easternmost Atlantic—during its 3-day track over Ireland and the UK (15–17 October 2017). Overall, the results reveal the significant accuracy of IBI-WAV forecasts and prove that a combined observational and modeling approach can provide a comprehensive characterization of severe wave conditions in coastal areas and shows the benefits from the complementary nature of both systems.

This paper showcases the one year-long (2014) multi-parameter skill assessment of Iberia-Biscay-Ireland (IBI) operational ocean forecasting system. The investigation is focused on a specific subdomain in the Northwestern Mediterranean where several observational networks encompassing both in situ and remote sensing instruments are available. This region is relevant since it includes two harbours and a marine protected area, the Ebro River Delta. Class-1 and class-2 skill metrics are used in concert to quantitatively evaluate the quality of hourly IBI surface fields. The impact of riverine discharges on the coastal circulation is investigated by comparing the signal of the Ebro River freshwater outflow in both observed (high-frequency radar (HFR)) and modelled (IBI) current maps. The ability of the HFR and IBI to detect the presence of coastal eddies is also qualitatively estimated by calculating surface vorticity maps. According to the results, basic circulation features are statistically reproduced by IBI in reference to mean and variance, despite some model drawbacks in terms of reduced energy content in surface currents. IBI has proven to be a robust model solution in the study area, able to act as a consistent large-scale ‘father’ system in future downscaling approaches by providing coherent open boundary conditions to nested high-resolution coastal models.

Observations from a high frequency radar system and outputs from a high resolution operational ocean model working at the Strait of Gibraltar have been analyzed and compared during the period February 2013 to September 2014 in order to evaluate their capability to resolve the surface circulation of the region. The description of the mean circulation patterns has been statistically assessed, showing good agreement, particularly in the central region of the strait corresponding with the Atlantic Jet (AJ) stream, although some short scale features are not reproduced by the model. In the frequency domain very high concordance is observed. Tidal maps of diurnal and semidiurnal constituents are in good agreement with previous observations. The analysis of the model and radar response to the wind forcing reveals that the low resolution of the model wind‐forcing field and its deeper superficial level smoothes the wind effect on the simulated currents. The first three EOF modes account for the 86% of model and radar variances. The coincidence between the observed and simulated patterns is very significant for the first two modes, which account for the mean velocity field and the latitudinal shifting of the AJ consequence of the flow‐topography interaction. The third mode captures the wind‐induced circulation, and greater discrepancies are found in this case. Results underline the complementary character of both systems: radar observations improve the model description, resolving short scale processes, while the model completes the radar information when the time or spatial coverage is poorer.