You have arrived at the Marine Heatwave (MHW) Tracker. This web application has been designed to show the most up-to-date information available on the occurrence of MHWs around the world, which is currently a two-week delay. The Marine Heatwave Tracker also hosts all of the historic MHW records for the entire planet going back to January 1st, 1982.

What is a Marine Heatwave (MHW)?

A MHW is generally defined as when the temperature in a given location is in the top 10% of temperatures ever recorded during that time of year for at least 5 straight days. For example, if the coastal waters off Durban in South Africa are roughly 22°C on any given April 1st, then if temperatures in excess of perhaps 28°C are recorded there in 2019 over March 28th to April 10th, this could be flagged as a MHW. This is a definition for MHWs first put forward by Hobday et al. 2016 . For a more detailed explanation with visuals please follow this link .

How do I use this?

This site works similarly to the Google maps we use in day-to-day life. Click and drag to move around the world. Use the mouse scroll wheel or click the plus/minus buttons on the left side of the screen to zoom in or out. The date box in the top right corner tells us which day is being shown on the map. Clicking in this box we can choose any date from the near present back to January 1st 1982. We can also choose to screen out the different categories of MHWs (see below) by clicking on the check boxes next to each category underneath the 'Time sereis' button. The legend can also be turned off by unchecking the legend option underneath the categories check-boxes. If one of the pixels on the map catches your eye, click on it to popup a little window that shows the longitude, latitude, and category of the MHW there. To get more information click on the 'Time series' button in the top right of the screen, underneath the date box. This will bring up a new window that contains more detailed information. This window currently contains two tabs: 'plot' and 'table'. We can download the climatology and threshold data for the chosen pixel when in the plot tab by clicking the download button at the bottom of the window. To download the temperature data please go to the NOAA website . The figure in the plot tab allows us to mouse-over the time series information to get immediate feedback on what the temperature, climatology, and threshold were on any given day. We can also select any desired range of dates to look at from the date selectors in the bottom left of the panel. The table tab shows a table of all of the MHWs that have ever occurred at the chosen longitude/latitude. This information is shown as a simple table and may be downloaded with by clicking the button in the bottom left corner of the of the window.

What do these colours mean?

In the map panel of the Marine Heatwave Tracker we can see that there is a particular colour palette being used. Each of these four colours corresponds to increasing categories of MHWs as first proposed in Hobday et al. 2018 . The first category, severe, is somewhat common and no category one MHWs have yet been recorded as causing lasting ecological or financial damage. The second category of MHWs, strong, are increasing the most rapidly of the four categories and are becoming as common as category one MHWs were when record keeping began in the 80's. Luckily, no category two MHWs have yet been documented as being destructive either. Category three MHWs, severe, are less common but can be devastating when they persist for multiple months. The last category, extreme, is thankfully a rare occurrence. It is now known that less than three months of a persistent category four MHW can destroy hundreds of kilometres of ocean ecosystems.

Where do these data come from?

The global satellite product used in the Marine Heatwave Tracker are the daily Optimally Interpolated Sea Surface Temperature (OISST) data that we can download from the National Oceanic and Atmospheric Administration (NOAA). These data are on an even 1/4 degree grid over the surface of the planet. The daily values go back as far as September 1st, 1981. More information about these data may be found here .

A tutorial for how to download these data in R may be found here , and a tutorial on how to calculate marine heatwaves from these data in R may be found here .

The marine heatwaves were calculated using the Hobday et al. 2016 definition briefly outlined above. The results on the MHW Tracker were calculated with the R version of this algorithm and extensive documentation on this may be found here . This algorithm is also available for python and MATLAB .

Who made this?

The Marine Heatwave Tracker was developed by Robert Schlegel and is an outcome of the Marine Heatwaves International Working Group . Therefore, this work has been directly and indirectly supported by several governmental, academic, and private organisations/funding bodies. The full list with links to further information is provided below in alphabetical order:

AU - Aberystwyth University

AIMS - Australian Institute of Marine Science

CLEX - ARC Centre of Excellence for Climate Extremes

CSIRO - Commonwealth Scientific and Industrial Research Organisation

DAL - Dalhousie University

MBA - Marine Biological Association

NESP - National Environmental Science Programme

OFI - Ocean Frontier Insitute

SAMS - The Sottish Association for Marine Science

UC - University of Canterbury

UNSW - University of New South Wales

UTAS - University of Tasmania

UW - University of Washington

UWA - The University of Western Australia

UWC - University of the Western Cape


Unfortunately this app is not currently optimised for use on mobile devices (e.g. cell phones or tablets). It will therefore appear rather clumsy if being viewed on a screen smaller than a laptop. There is currently not a plan to address this issue.

To report any bugs or to provide any other feedback on the app please contact the developer at: robert.schlegel@dal.ca

How do I cite this app?

To cite the app itself please use:

Schlegel, R. W. (2018). Marine Heatwave Tracker: The app to see when and where marine heatwaves are happening around the world. http://www.marineheatwaves.org/tracker


The marine heatwave data displayed in this app were calculated with the `heatwaveR` R package. To cite `heatwaveR` in publications use:

Schlegel, R. W., & Smit, A. J. (2018). heatwaveR: A central algorithm for the detection of heatwaves and cold-spells. The Journal of Open Source Software, 3, 821.

The definition and categorisation of marine heatwaves may be found in the following two papers:

Hobday, A. J., Alexander, L. V., Perkins, S. E., Smale, D. A., Straub, S. C., Oliver, E. C., ... & Holbrook, N. J. (2016). A hierarchical approach to defining marine heatwaves. Progress in Oceanography, 141, 227-238.

Hobday, A. J., Oliver, E. C., Gupta, A. S., Benthuysen, J. A., Burrows, M. T., Donat, M. G., ... & Smale, D. A. (2018). Categorizing and naming marine heatwaves. Oceanography, 31(2), 162-173.