Given the availability of an SST climatology, it is possible to specify the difference between the SSTs over the region for some month and their climatological (i.e. expected) values. These differences are called anomalies. The example shows the monthly mean SST for March 1999, and its anomaly map.

The first image shows the mean SST over the region for the month, while the second image indicates the difference between the first image and the long-term mean for this month (the example given in the description of the SST climatology). Positive differences in the second image indicate that the SSTs in such regions are warmer than the long-term mean, while negative differences indicate the reverse. Significant anomalies are often associated with ocean circulation changes, as in the case of the East Cape Current here.

As the ocean responds slowly, these analyses may be useful for predicting SST changes up to a few months in advance.

Usage Notes

The following points should be considered when using the monthly SST analyses and anomalies:

• If no SST data are available for some location, then it will be coloured as for the land areas. This colour will change from month to month, but the interpretation is always the same.
• It is possible for an anomaly to appear cold (or warm) simply because there was a prolonged data outage during the month. This is not usually the case, but has happened (e.g. April 1997, where data were only available for the first 22 days of the month).
• Early 1993 data show a small cold bias. This arises from the lingering effects of the stratospheric dust from Mt Pinatubo, and is thought to be around -0.20°C.