the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 01 Sep 2026
Suppression of local upwelling in the Gulf of Panama predicted a season in advance
Abstract. Wind-driven upwelling of subsurface ocean waters to the surface ensures nutrient-rich waters reach the epipelagic zone, supporting some of the most diverse ecosystems and largest fish stocks in the global ocean. In early 2025, the Gulf of Panama experienced a collapse of the local upwelling system not previously observed in historical records, with notable impacts on regional physical and biogeochemical conditions. Predictability of upwelling collapse in relatively local systems on seasonal timescales has yet to be assessed. Here, the predictability of upwelling in the Gulf of Panama is explored in an operational seasonal forecasting system. First, the extreme weakening of the northerly jets driving upwelling and the corresponding extreme sea surface temperatures of 2025 are shown to have been accurately predicted a season in advance. Crucially, hindcasts from the period 1993 to 2024 demonstrate high probabilistic and deterministic skill, and also capture the strong upwelling of 1998. By validating against a high-resolution global ocean reanalysis, an increase in temperature forecast skill with depth is uncovered, making the case for exploiting subsurface information for improved early-warning and description of upwelling events. Lastly, the occurrence of warm upwelling, specifically in 1998, raises a discussion of the most suitable upwelling indicators for the region. The seasonal forecast system sufficiently resolves wind stress-derived Ekman Pumping and the exceptionally weak vertical ocean velocity in 2025. This study demonstrates the capability of seasonal forecasts to provide early warning of upwelling collapse.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-5138', Anonymous Referee #1, 30 Sep 2026
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RC2: 'Comment on egusphere-2026-5138', Anonymous Referee #2, 26 Oct 2026
Review of McAdam et al. Suppression of Local Upwelling in the Gulf of Panama Predicted a Season in Advance (manuscript submitted to EGUsphere)
The manuscript addresses a highly relevant topic: the seasonal prediction of coastal and oceanic upwelling. It focuses on an upwelling system that differs from the four classical Eastern Boundary Upwelling Systems (EBUSs) of California, Canary, Humboldt, and Benguela, namely the Gulf of Panama. In this region, upwelling is primarily driven by wind jets associated with mountainous topography, topographic gaps, and offshore-directed winds, in a manner similar to the Gulf of Tehuantepec system further north (Trasviña et al., 1995), visible in Figure 1 near 10°N. It would also be interesting to assess/comment whether a similar suppression of upwelling was observed in the neighboring Gulf of Tehuantepec system during 2025.
The main issue addressed in this manuscript is the seasonal predictability of this upwelling system within operational ocean forecasting frameworks. The study investigates the predictability of the atmospheric forcing responsible for upwelling, namely wind stress and wind stress curl, and applies this analysis to the exceptionally anomalous conditions observed in 2025, which substantially affected the seasonal upwelling regime.
Furthermore, the manuscript does not explicitly describe or discuss the causes of the wind anomalies that drove the upwelling anomaly observed in 2025. Understanding these mechanisms is important, particularly since they were briefly addressed in the study by O'Dea et al. (2025), from which the subsurface temperature data used in the present analysis were used. Such information would help place the reported upwelling suppression into a broader dynamical context and provide further insight into the sources of seasonal predictability
A hindcast analysis covering the period 1993-2024 is also conducted, using high-resolution reanalysis products (GLORYS) as a validation reference. The objective is to demonstrate the capability of operational forecasting systems to provide skillful seasonal forecasts and to support the development of early warning systems. Indeed, the hindcast results raise several questions regarding the oceanographic and atmospheric conditions of some of the years highlighted in the analysis (e.g., 1998), particularly in relation to ENSO, as well as issues associated with long-term trends that are not addressed in the present manuscript. This section appears somewhat disconnected from the main focus of the study, namely the 2025 upwelling anomaly and its seasonal predictability, as reflected in the manuscript title.
I understand that the authors include the hindcast analysis to demonstrate the model's ability to reproduce the system's past dynamics. However, hindcast skill and forecast skill are not necessarily equivalent. Consequently, a greater effort should be made to establish a clearer connection between the hindcast and forecast components of the study, explaining how the former supports confidence in the prediction of the 2025 event and how both analyses contribute to the scientific message of the manuscript.
On the other hand, I have difficulty understanding the message conveyed by Figure 6.
My interpretation is that ERA5 captures the anomaly in wind stress curl and the associated vertical velocities (Ekman pumping) reasonably well (top row); that CMCC-SPS4 only weakly detects this anomaly (except perhaps in January); and that the anomaly in ocean-model vertical velocity (W) is nevertheless reproduced with reasonable skill. If this interpretation is correct, I believe the authors should explain more clearly why the oceanic response appears to be captured despite the weak representation of the atmospheric forcing anomaly.
Additional Considerations
In the Introduction, the manuscript cites the example of Sylla et al. (2026) as being associated with the Benguela EBUS. However, that region appears to belong more appropriately to the Canary EBUS. Please verify and clarify this point.
The manuscript refers to the CMS Wind Stress product, but the description provided is insufficient for readers to identify the exact data source. Please provide additional information and/or a direct link to the product. I could not find a corresponding bibliographic reference.
Around line 105, the manuscript states: “We rely on an in-house forecast system...” It is not clear how this system differs from the original CMCC-SPS4 forecasting system. Please provide a more detailed description of the differences, if any.
What is the reference for the AUC metric? The current description does not seem sufficient, especially since AUC is not a widely used statistical indicator in oceanography. Please explain in more detail how it is calculated and what advantages it offers compared with more conventional skill metrics.
In Appendix A, what exact region is used for the calculations? The text refers to “the wider upwelling region (Figure 1)”, but Figure 1 appears to encompass both the Pacific and Caribbean sectors. Please clarify this point. Is the region instead the rectangle shown in Figure 2? If so, this should be explicitly stated.
Discussion and Conclusions
The discussion should more clearly highlight the unique characteristics of the Gulf of Panama upwelling system. According to O'Dea et al. (2025), "...this process occurs with remarkable predictability when the Intertropical Convergence Zone reaches its southernmost position (January-April), generating northerly trade winds that funnel through the topographic low of the Canal Zone to form the Panama low-level jet and drive strong nearshore upwelling across ~60,000 km² of Pacific Ocean."
The manuscript presents this case as a successful example of seasonal prediction of coastal upwelling. However, it does not sufficiently emphasize that the predictability may be inherently linked to the predictable nature of the underlying atmospheric forcing mechanism itself.
Furthermore, in paragraph 250, the authors state:
“This work proves the potential of operational seasonal forecasting systems to provide early warnings in the region, and suggests other local-scale or seasonal upwelling systems should be the target of future studies.” The discussion then relates these findings to studies of predictability in more typical EBUSs. However, given that the present work examines a tropical upwelling system whose predictability may be substantially greater than that of mid-latitude upwelling systems, I have strong reservations about how broadly these conclusions can be generalized. Demonstrating skill in this specific tropical system does not necessarily imply comparable predictability in the classical EBUS. I believe this limitation should be discussed explicitly, with greater emphasis placed on the particular dynamical characteristics of the Gulf of Panama system.
More generally, the issue of extending these conclusions to other EBUSs deserves a more thorough treatment. Based on current understanding of mid-latitude systems, particularly in the Northern Hemisphere (e.g., the California and Canary upwelling systems), seasonal predictability on timescales of several months is strongly constrained by atmospheric variability associated with upwelling-favorable winds. These winds are linked to large-scale mid-latitude anticyclonic systems, such as the Azores High, whose variability is considerably more difficult to predict at seasonal lead times.
Therefore, while the results presented here are promising and highly relevant for the Gulf of Panama, additional caution may be warranted when extrapolating them to classical Eastern Boundary Upwelling Systems.
Cited Literature
Trasviña, A., Barton, E. D., Brown, J., Vélez, H. S., Kosro, P. M., & Smith, R. L. (1995). Offshore wind forcing in the Gulf of Tehuantepec, Mexico: The asymmetric circulation. Journal of Geophysical Research: Oceans, 100(C10), 20649-20663.
Citation: https://doi.org/10.5194/egusphere-2026-5138-RC2
Data sets
Supplementary forecast data for "Suppression of local upwelling in the Gulf of Panama predicted a season in advance" by McAdam et al. (Version 1) R. McAdam and A. Sanna https://doi.org/10.5281/zenodo.21723336
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Summary
In this work, the authors are exploring the predictability of upwelling in the Gulf of Panama using the Euro-Mediterranean Centre on Climate Change Seasonal Prediction System version 4 (CMCC-SPS4). They find that useful prediction skill exists at lead times of up to 3 months in advance. Furthermore, the unprecedented weakening (strengthening) of the upwelling in 2025 (1998) had been accurately predicted, using the Ekman pumping has the main index to characterize the Gulf of Panama upwelling system.
In general, the manuscript fits the scope of Ocean Sciences and the research reported is of great interest for the readership.
Major comments
1) Analysis is needed regarding the characteristics of the Gulf of Panama ( GoP) Upwelling. What is the seasonality of SST and wind variability in the region? For this purpose, it would be helpful to see a figure with the seasonal cycle of SST and wind stress standard deviation in the target region. Furthermore, explain more to what extent the relatively high prediction skill in the region could be translate into useful information for fisheries.
2) Authors suggested that the exceptional SST events are attributed to a weak upwelling, but this relation seems not to hold in 1998 and 2016 (Fig.3). For that, It would be of interest to see a figure about the relative importance of thermodynamic, i.e the individual components of the net heat flux versus dynamic influences (Ekman pumping) on SST in the GoP. Also, Could coastally trapped waves be an additional factor complicating upwelling in the GoP? Could they be responsible for the lag between wind forcing and SST response mentioned in ll. 205-207?
3) The Ekman Coastal Upwelling cannot be ignored in the most of Eastern boundary current. I think it must be important to provide a figure of comparison between the transport based on Coastal Upwelling and Ekman pumping. For this purpose it would be a justification about the choice of Ekman pumping index only.
4) As noted, Ekman suction and coastal divergence are calculated separately (Eq.1 and Eq.2), but are not really independent in the calculation. Instead, one can unambiguously calculate the total divergence associated with Ekman divergence + Ekman suction by integrating the Ekman transport along all boundaries (north, south, east) of the region of interest. I don't think Ekman suction and coastal divergence should be treated separately anyway, as they overlap spatially. Thus, I recommend calculating the total divergence by integrating the Ekman transport along all boundaries.
5) Authors described briefly the role of ENSO on the GoP’s upwelling, but a figure of forecasting Ekman pumping and SST during some selected years of ENSO events would also be interesting. This helps readers better understand the role of ENSO on the GoP’s prediction.
6) Does the model allow to draw conclusion about a trend in upwelling intensity throughout the selected time scale (1993-2025) - does it increase/decrease or is there no trend? That would also be interesting to evaluate the predictability.
7) I gather that the authors use the wind stress provided by the atmospheric components for their calculations (Eq.1 and Eq.2). There is, however, also the wind stress actually seen by the ocean (i.e. interpolated to the ocean grid), which is available perhaps for the model and/or observations in your target region. I believe the authors should check for a few whether using ocean wind stress makes an appreciable difference.
8) There are many different observational data sets used for validation, and they have different spatial resolutions, cover different time periods, and use different methods (e.g., remote sensing vs.model reanalysis). Why not use a reanalysis that provides everything in a consistent way or interpolate all in the some grid.
Minorcomments
L29-30: In the EBUS, upwelling is predictable on seasonal timescales, as shown for the California (Siedlecki et al., 2016; Amaya et al., 2024) and Southern Canary Upwelling System (Sylla et al., 2026) systems. Not Benguela, please correct.
L43-44: Seasonal forecasting systems are typically reliable in the Eastern Tropical Pacific, where interannual variability is largely governed by the El Nino Southern Oscillation (ENSO, eg; Jacox et al.2017, 2026). Please add these references
L68: “the global ocean” rather than “the global oceans”
L84 :‘’Here, daily values of average of nighttime temperatures were calculated’’ instead of “was calculated”
L99: ocean and atmospheric analyses; for the operational period (2025 onwards). Please remove the semicolon (;) and start a new sentence from “For the operational’’…...
L107: local-scale upwelling indices (Capet et al., 2004), please add also Small et al. 2015 (
Small, J. R., Curchitser, E., Hedstrom, K., Kauffman, B. and Large, W. G. (2015) ‘The Benguela upwelling system: Quantifying the sensitivity to resolution and coastal wind representation in a global climate model’, Journal of Climate, 28(23), pp. 9409–9432. doi: 10.1175/JCLI-D-15-0192.1)
L120-126: Reference(s) needed here for Ekman Pumping and Ekman Coastal Upwelling calculation
L218-219: “ the wind anomaly for the upwelling season in 2016 was relatively weak (you mean intense?). That's not what I see in Figure 3, please clarify
L218: Enso influences SST in this region but not the wind whereas in the paper, this latter is described as the main drivers for SST variability. Please clarify
References
Jacox MG, Alexander MA, Stock CA et al (2017) On the skill of seasonal sea surface temperature forecasts in the california current system and its connection to enso variability.
Jacox, M. G., Edwards, C. A., Hazen, E. L.,& Bograd, S. J. (2018). Coastal upwelling revisited: Ekman, Bakun, and improved upwelling indices for the U.S. West Coast. Journal of Geophysical Research: Oceans, 123. https://doi.org/10.1029/
Jacox, Michael G., et al. "Seasonal-to-interannual prediction of North American coastal marine ecosystems: Forecast methods, mechanisms of predictability, and priority developments.Progress in Oceanography 183 (2020): 102307.
Small, J. R., Curchitser, E., Hedstrom, K., Kauffman, B. and Large, W. G. (2015) ‘The Benguela upwelling
system: Quantifying the sensitivity to resolution and coastal wind representation in a global climate model’, Journal of Climate, 28(23), pp. 9409–9432. doi: 10.1175/JCLI-D-15-0192.1