Store
My Account

SST anomalies by region

Sea Surface Temperature Anomalies

Daily maps of how much warmer or cooler the sea surface is than normal for the time of year, from the 1 km GHRSST-MUR satellite analysis. Step back through the last month with the arrows.

Region
Map
Heatwaves

   
Loading…

White contours every 0.5 °C; black lines are depth contours; white dots mark cities and towns. Each region keeps one colour scale for the whole month so days can be compared. The newest map is usually three days old; maps update once a day. Click Moderate–strong or Severe–extreme to show or hide that heatwave category; the animation shows the map with and without both. See Methods below.

Methods

Sea surface temperature anomaly (map colours)

The colours are the daily GHRSST Multi-scale Ultra-high Resolution (MUR) v4.1 foundation SST analysis from NASA JPL (0.01°, about 1 km), expressed as the difference from JPL’s MUR daily climatology for 2003–2014. The anomaly product is made by NOAA SWFSC ERD and served on NOAA CoastWatch ERDDAP (dataset jplMURSST41anom1day); it is used as published, not recalculated here. The most recent four days are revised daily, so those maps are redrawn as the data change.

The 0.5 °C contours are drawn from the anomaly field smoothed over about 20 km, so they follow the broad pattern rather than every eddy. The colour scale for each region spans the 2nd to 98th percentile of all anomalies in the month shown, widened to whole 0.5 °C steps.

Marine heatwaves (overlays)

Marine heatwaves follow the definition of Hobday et al. (2016): sea surface temperature above a seasonally varying 90th-percentile threshold for at least five consecutive days, with breaks of two days or less counted as one event. They are calculated from NOAA OISST v2.1 (0.25°, about 25 km), the standard dataset for this method:

  • Baseline: 1991–2020. For each day of the year, the climatological mean and 90th percentile are taken from an 11-day window centred on that day, then smoothed with a 31-day running mean.
  • Recent data: final OISST, plus preliminary OISST for the last two weeks or so. The 40 days before the month shown are included, so heatwaves that were already under way are classified correctly.
  • Categories (Hobday et al. 2018) are set by how far SST is above the mean, in multiples of the gap between the 90th-percentile threshold and the mean: I Moderate (1–2×), II Strong (2–3×), III Severe (3–4×) and IV Extreme (more than 4×). The Moderate–strong overlay (cyan) shows categories I–II; the Severe–extreme overlay (red) shows III–IV.

Reading the two layers together

  • Different baselines. The colours compare with 2003–2014; the heatwaves compare with 1991–2020. The two periods have different averages, so the colour at a spot does not map exactly onto its heatwave status: a moderately warm colour can sit inside a heatwave outline, and a warm colour can sit outside one.
  • Different resolutions. Heatwave outlines are 25 km features drawn over 1 km colours, so they are smoother and do not follow fine coastal detail.
  • Recent days can change. A warm spell is only marked once it has lasted five days, and preliminary OISST is revised, so outlines for the last week or so may appear or shift on later days.

References

  • Chin, T.M., Vazquez-Cuervo, J. and Armstrong, E.M. (2017). A multi-scale high-resolution analysis of global sea surface temperature. Remote Sensing of Environment 200, 154–169.
  • Hobday, A.J. et al. (2016). A hierarchical approach to defining marine heatwaves. Progress in Oceanography 141, 227–238.
  • Hobday, A.J. et al. (2018). Categorizing and naming marine heatwaves. Oceanography 31(2), 162–173.
  • Huang, B. et al. (2021). Improvements of the Daily Optimum Interpolation Sea Surface Temperature (DOISST) Version 2.1. Journal of Climate 34, 2923–2939.
  • Marine heatwave overview: marineheatwaves.org