Marine Heatwaves


Marine heatwaves are periods of persistent anomalously warm ocean temperatures, which can have significant impacts on marine life as well as coastal communities and economies. Scientists at PSL are working to characterize marine heatwaves, understand how they form and dissipate, and predict them in advance. On this page, we will provide current ocean maps, forecasts of heatwaves, interactive tools for users to explore ocean heatwaves themselves, links to research results and to webpages at other institutions.

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Global Marine Heatwave

Observed Condition

To reference plot in a publication, please cite as "Image provided by the NOAA Physical Sciences Laboratory, Boulder, Colorado from the website at ".

Q&A for the interactive tool

  • How to interact with the map
  • What is a percentile and how is it used to define a MHW
  • Why does the sea surface temperature (SST) trend matter
  • How to interact with the time series
  • What are the rankings

Further questions please contact

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To reference plot in a publication, please cite as "Image provided by the NOAA Physical Sciences Laboratory, Boulder, Colorado from the website at ".

Q&A for the forecast tool

  • How to interact with the map
  • What is marine heatwave
  • What models are used to generate the prediction
  • Why does the sea surface temperature (SST) trend matter
  • What is prediction skill

Further questions please contact

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High Resolution Sea Surface Temperature

User Options

Dataset* :
Region :
Frequency :
Statistic :
Year* :
Month* :
Day* :

(LMEs) map showing the associated ID number and name.

* availibility for date (year, month, day) options.

Creating Plot ⏳

Marine Heatwave Forecast Monthly Report

Forecast initial time June 2024
Forecast period June 2024 - May 2025

Global Marine Heatwave Forecast Discussion

Observed and forecasted values include the effects of long-term warming. Values with the long-term warming trend removed are in brackets.

Current marine heatwave conditions:

In May 2024, 37% [24%] of the global ocean experienced MHWs, which ranked 7th [8th] among all months since 1991.

While the fraction of the globe with marine heatwave (MHW) conditions remained relatively unchanged from April, those along the equator in the tropical Pacific decreased as El Niño weakened. MHWs are currently found in the tropical Pacific except near the equator east of the dateline, across much of Pacific to the east of Japan, the Sea of Japan and South China Sea, much of the tropical and eastern Atlantic, the Gulf of Mexico, the Caribbean Sea, south of Iceland and around the British Isles, much of the central and western tropical Indian Ocean, and portions of the Atlantic, Indian and Pacific sectors of the Southern Ocean.

Marine heatwave forecasts:

Forecasts predict that MHW coverage and overall intensity will continue to decline in the coming months (especially in the eastern and central tropical Pacific and Atlantic basins), dropping to ~29% [15%] of the global oceans experiencing MHW conditions by October 2024. Below is a regionally refined focus:

  • Tropical Pacific - MHW conditions, associated with a dissipating El Niño event, are predicted to continue to decrease over most of the equatorial Pacific, with little chance of a MHW in the eastern ~⅔ of the basin (0-10% [0-10%]; high confidence). However, MHWs are forecasted to decrease but still persist in a band extending southeastward from southeast Asia to the central south Pacific by October (50-70% [10-30%]; low-medium confidence).
  • North Pacific - Forecasts show limited risk of MHW conditions along the west coast of North America through fall (0-20% [0-10%]; low-medium confidence). In the central North Pacific, MHWs are forecasted to persist through November (40-70% [20-40%]; low confidence), as are MHWs near Japan (40-80% [20-60%]; low-medium confidence).
  • Tropical Atlantic - MHW conditions in the tropical North Atlantic are likely to persist through October 2024 (80-100% [50-80%]; low-medium confidence). MHWs in the tropical South Atlantic are expected to diminish through austral (southern) winter.
  • Caribbean Sea - MHW conditions are forecasted to persist in the Caribbean Sea through October (70-100% [50-80%]; low-medium confidence).
  • North Atlantic - While predicted to decrease, there is still a relatively high probability that MHW conditions will persist through summer in the northeast Atlantic from Northern Africa to Europe and extending northwestward to southeast Greenland (30-60% [20-60%]; low confidence). There is an elevated risk of MHWs along portions of the east coast and the Gulf Stream/North Atlantic Current through September 2024, (30-80% [20-50%]; low confidence).
  • Indian Ocean - Elevated chances of MHW conditions are predicted over much of the Indian Ocean north of ~25°S through September 2024 (40-100% [10-40%]; low-medium confidence), with the highest probabilities off the east African coast north of Madagascar.
  • Southern Ocean - MHWs in the Southern Ocean are forecasted to occur south of Africa, south of Australia and in the central Pacific (70-100% [50-90%]; low confidence).

How confidence levels are determined

Marine Heatwave Maps

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Marine Heatwave Map (warming trend preserved)

Click on the image to have a full screen view!

Marine Heatwave Area Percentage - Monthly Forecast

How the ocean basins are defined

Remove long-term temperature trends?

Marine Heatwave Area Percentage Forecast (warming trend preserved)

Click on the image to have a full screen view!

Marine Heatwave Area Percentage - Historical Record

Marine Heatwave Area Percentage

Click on the image to view forecast plume!


Web Based Tools for looking at Marine Heatwaves

PSL has several web-based tools for plotting and analyzing gridded datasets and timeseries. With these tools, you can extract time-series from different regions, plots maps of means and anomalies, create correlations maps, and analysis time-series. We are also expanding upon what these tools can do.

List of tools

  • WRIT Ocean Maps and Vertical Crossections

    Allows users to make maps and vertical cross-sections from various reanalyses. Statistics include means, anomalies and climatologies. Users can also difference the various reanalyses for all three types of statistics (for any overlapping date in the reanalyses). Composites (averaging multiple dates) are also available.

  • WRIT Ocean Time-series Extraction and Analysis
  • Extracts timeseries at specified latitude/longitude or latitude/longitude ranges and either plots the time-series, time-series differences, and scatter plots. Various statistics are returned in addition to numeric values of the time-series plotted. Ability to plot and compare climate index time-series such as the PNA or Niño3.4 or upload your own.

  • WRIT Ocean Correlation Maps Vertical Crossections.

    Calculates correlations (and regressions) of the reanalysis and observational dataset with supplied atmospheric/ocean indices or user uploaded time-series. Users can plot correlations at different lead/lags. They can also create vertical cross-section correlation plots.

PSL Publications

Refereed Papers

  • Xu, T., M. Newman, A. Capotondi, S. Stevenson, E. Di Lorenzo, and M. A. Alexander (2022): An increase in marine heatwaves without significant changes in surface ocean temperature variability, Nat. Commun., 13, 7396,
  • Jacox, M. G., M. A. Alexander, D. J. Amaya, E. Becker, S. J. Bograd, S. Brodie, E. L. Hazen, M. Pozo Buil, and D. Tommasi (2022): Global seasonal forecasts of marine heatwaves, Nature, 604, 486-490,
  • A. Capotondi, M. Newman, Xu, T., and E. Di Lorenzo (2022): An Optimal Precursor of Northeast Pacific Marine Heatwaves and Central Pacific El Niño Events, Geophys. Res. Lett., 49 (5), e2021GL097350,
  • Amaya, D. J., M. A. Alexander, A. Capotondi, C. Deser, K. Karnauskas, A. J. Miller and N. Mantua (2021): Are Long-Term Changes in Mixed Layer Depth Influencing North Pacific Marine Heatwaves?. Bull. Amer. Meteor. Soc., 102 (1), S59-S66,
  • Xu, T., M. Newman, A. Capotondi and E. Di Lorenzo (2021): The Continuum of Northeast Pacific Marine Heatwaves and Their Relationship to the Tropical Pacific. Geophys. Res. Lett., 48 (2), 202GL090661,
  • Jacox, M. G., M. A. Alexander, S. J. Bograd and J. D. Scott (2020): Thermal displacement by marine heatwaves. Nature, 584, 82-86,
  • Jacox, M. G., D. Tommasi, M. A. Alexander, G. Hervieux and C. A. Stock (2019): Predicting the Evolution of the 2014–2016 California Current System Marine Heatwave From an Ensemble of Coupled Global Climate Forecasts. Front. Mar. Sci., 6, 497,
  • Alexander MA, JD Scott, KD Friedland, KE Mills, JA Nye, AJ Pershing, AC Thomas, (2018): Projected sea surface temperatures over the 21st century: Changes in the mean, variability and extremes for large marine ecosystem regions of Northern Oceans. Elementa: Science of the Anthropocene, 6(1):9,
  • Scannell, H. A., A. J. Pershing, M. A. Alexander, A. C. Thomas and K. E. Mills (2016): Frequency of marine heatwaves in the North Atlantic and North Pacific since 1950. Geophys. Res. Lett., 43 (5), 2069-2076,

Marine Heatwave Related Datasets

Marine Heatwave Forecast

The forecast generated by Jacox et al., 2022

SST Datasets at PSL

Ocean Reanalyses at PSL

Ocean Time-series at PSL



  • The California Current Marine Heatwave Tracker
    Developed by oceanographers from NOAA Fisheries' Southwest Fisheries Science Center as an experimental tool for natural resource managers, the California Current MHW Tracker is a program designed to understand, describe, and provide a historical context for the 2014-16 blob. It also produces a range of indices that could help forecast or predict future MHWs expected to impact the CA coast. (NOAA Integrated Ecosystem Assessment)
  • Marine Heatwave Monitoring and Forecast
    Developed by oceanographers from NOAA/NCEP Climate Prediction Center, the webpage provides an overview on the marine heatwave diagnostics based on observational data and marine heatwave forecast based on NMME/CFSv2. (NOAA/NCEP Climate Prediction Center)
  • Marine Heatwaves Organization
    From the Marine Heatwaves International Working Group which is dedicated to ​understanding marine heatwaves: their physical drivers, climatological properties, and ecological impacts. The webpage summarizes their research. (
  • California's Marine Heatwaves FAQ
    Explore this FAQ to learn more about what is causing marine heatwaves and their impacts in California. (UC San Diego/Scripps)
  • Ocean Heatwaves
    Key concepts about marine heatwaves with an emphasis on heatwaves and climate change. (Climate Central)
  • ENSO and Marine Heatwaves
    A an interview with two PSL scientists about marine heatwaves, what causes them, how they are impacted by ENSO and how climate change might impact their frequency, among other topics. (
  • Looking back at the BLOB: Marine Heatwave
    A history of the development of and the demise of the famous "Blob", the 2015-16 heat wave in the NE Pacific ocean. (NOAA Fisheries News)


  • Python code that defines marine heatwaves from SST data


This is a Research and Development Application