The study, carried out by Axel Hidalgo-Mayo of the Institute of Meteorology in Havana, Cuba, builds its climatology on the ERA5 reanalysis, a state-of-the-art reconstruction of past weather produced by the Copernicus Climate Change Service. Reanalysis products combine historical observations with a numerical weather model to produce a physically consistent record of winds and waves stretching back decades. To make sure the reanalysis could be trusted in this particular basin, the author validated it against eight wave-measuring buoys operated by the United States National Data Buoy Center. The agreement was strong: the median Spearman correlation between modeled and observed significant wave height reached 0.928, and the Perkins Skill Score, a measure of how well the full statistical distribution of wave heights matches observations, averaged 91.6 percent. Those numbers matter, because every conclusion about long-term trends rests on the fidelity of the underlying record.

Significant wave height, abbreviated Hs, is the standard metric oceanographers use to characterize sea state; it corresponds roughly to the average height of the highest one-third of waves and is the quantity engineers use when designing platforms, breakwaters and coastal defenses. Rather than treating the Gulf of Mexico and the Caribbean Sea as a single homogeneous basin, the study identifies three physically distinct wave regimes. The eastern Caribbean is sustained almost continuously by the Caribbean Low-Level Jet, a persistent river of fast-moving air that funnels through the mountain passes of Central America and blows steadily across the basin, producing waves with a coefficient of variation of just 0.38, meaning the sea state there is remarkably regular. The western Caribbean, by contrast, acts as a cyclone intensification zone where hurricanes passing over warm waters whip up episodic, extreme forcing. The Gulf of Mexico is dominated by a third mechanism entirely: seasonal cold fronts that sweep down from North America each winter, generating rough seas with a coefficient of variation of 0.54, the most variable of the three regimes.

With the climatology established, the study turned to the central question of trend detection. Detecting a genuine long-term trend in noisy geophysical data is notoriously difficult, and naive statistical tests can be fooled by autocorrelation, the tendency of consecutive years to resemble one another, and by heteroscedasticity, the tendency of variability to change over time. The analysis therefore applied Mann-Kendall trend tests with corrections for both effects, and then controlled the False Discovery Rate across thousands of grid points so that the handful of apparently significant results were not statistical flukes. The outcome was a sharp seasonal dichotomy. During the heart of the Atlantic hurricane season, the months of August, September and October, the 99th-percentile significant wave height, a robust index of extreme seas, shows significant increasing trends across 33.2 percent of the grid points in the northwestern Caribbean. Averaged over that region, the trend amounts to an increase of 0.254 meters per decade, with individual locations rising as fast as 0.606 meters per decade, results that remain significant at the p < 0.001 level after correction for multiple testing.

The winter months tell the opposite story. During November, December and January, when cold fronts rather than hurricanes dominate the wave climate, only 3.3 percent of grid points show any significant trend, a fraction consistent with pure statistical noise. In other words, the intensification of extreme waves is not a basin-wide drift but a seasonally and geographically concentrated phenomenon tied to the cyclone season, and specifically to the corner of the Caribbean where hurricanes most often pass through or intensify. This spatial and seasonal specificity is itself an important finding, because it rules out explanations that would require the entire basin to be changing uniformly, and it points instead at changes in the behavior or tracks of tropical cyclones.

The most dramatic result concerns a structural break in the record. Using the Pettitt change-point test, a non-parametric method for locating the moment when a time series shifts from one statistical regime to another, the analysis identifies a dominant break in 1995 or 1996 in the northwestern Caribbean. That timing is not arbitrary: the mid-1990s mark the transition of the Atlantic Multidecadal Oscillation into its warm phase, a well-documented shift in North Atlantic sea surface temperatures that has been linked in earlier research to the marked increase in Atlantic hurricane activity documented since 1995. The wave record, in effect, carries the fingerprint of that large-scale oceanic reorganization. Before the break, extreme waves in the region followed one statistical distribution; after it, they followed a demonstrably more severe one.

To quantify what that regime change means in practical terms, the study employed a peaks-over-threshold analysis, the workhorse of extreme-value statistics. Wave heights exceeding the local 99th-percentile threshold were extracted, with a seven-day declustering window applied so that the multiple large waves generated by a single storm count as one independent event rather than many. The exceedances were then fitted with a Generalised Pareto Distribution, from which the fifty-year return period wave height, the level expected to be exceeded once every fifty years on average, could be estimated for each period. In the cluster of 369 grid points identified by Local Indicators of Spatial Association analysis as a high-high hotspot of extreme wave change, the fifty-year return value rose from 5.90 meters in the 1979 to 1995 period to 9.81 meters in the 1996 to 2024 period, a change of 4.23 meters with a within-cluster spatial standard deviation of 1.84 meters. The shape parameter of the fitted distribution, which controls how heavy the tail of the distribution is, increased from 0.226 to 0.522, indicating that the most extreme events became not just more frequent but fundamentally more probable at very high levels.

Such a large jump invites skepticism, and the study addresses it directly. Because neighboring grid points in a reanalysis are not statistically independent, a spatial thinning sensitivity check was performed to confirm that the result survives when the effective sample size is reduced to account for spatial autocorrelation. It does. Meanwhile, the opposing low-low cluster, a region where extreme waves have become less severe, records a decrease of 1.98 meters with a standard deviation of 1.35 meters, a pattern consistent with the stability of the cold-front-driven regime. The contrast between the two clusters reinforces the interpretation that the change is real, spatially structured and physically meaningful rather than an artifact of the method.

The implications reach well beyond academic climatology. Ports, offshore energy installations, coastal highways and tourism infrastructure throughout the Gulf of Mexico and the Caribbean have historically been designed using return-period wave heights computed under the assumption of stationarity, the idea that the statistics of the past reliably describe the future. This study demonstrates that the assumption fails in the northwestern Caribbean: a structure designed in 1990 for a fifty-year wave of about six meters could now face seas approaching ten meters over its lifetime. Updated probabilistic design baselines of the kind this analysis provides are therefore not a luxury but a necessity for engineers and planners in the region, particularly as coastal populations and assets continue to grow along the hurricane-exposed shores of Mexico, Cuba and Central America.

Scientifically, the work adds a wave-based perspective to a debate that has mostly been conducted in terms of hurricane counts and wind speeds. Because significant wave height integrates the effect of storm intensity, duration and track within a single observable quantity, it offers an independent line of evidence on how tropical cyclone behavior has evolved. The alignment of the 1995-1996 break with the Atlantic Multidecadal Oscillation transition, the concentration of trends in the cyclone season, and the stability of the cold-front regime together paint a coherent picture: the extreme wave climate of this basin is governed by distinct forcing mechanisms, and it is the hurricane-driven one that has stepped into a new, more dangerous state. All data underlying the study are publicly available through the Copernicus Climate Data Store, allowing other researchers to scrutinize and extend a record that now documents nearly half a century of a changing sea.

Subject of Research: Long-term trends and regime changes in extreme significant wave height in the Gulf of Mexico and Caribbean Sea from 1979 to 2024

Article Title: Climatology, trends, and regime changes of extreme wave conditions in the Gulf of Mexico and Caribbean Sea (1979–2024)

Article References: Hidalgo-Mayo, A. (2026). Climatology, trends, and regime changes of extreme wave conditions in the Gulf of Mexico and Caribbean Sea (1979–2024). Theoretical and Applied Climatology, 157(10), Article 626. https://doi.org/10.1007/s00704-026-06564-6

Image Credits: AI Generated

DOI: 10.1007/s00704-026-06564-6

Keywords: wave climate, significant wave height, Gulf of Mexico, Caribbean Sea, extreme value analysis, ERA5 reanalysis, tropical cyclones, Atlantic Multidecadal Oscillation, return periods, climate trends, Mann-Kendall test, coastal engineering