If a long time series of SSTs exists for some location, then it is possible to estimate what the “normal” SST for that location is. Often this will be expressed as a series of numbers, perhaps one for each month of the year.
Using a very large dataset of satellite SST observations, NIWA scientists have computed estimates of the mean monthly SST for every location over the standard coverage area. The results can be shown as a map, as in the example here, which is for March and the New Zealand region.
Accordingly, the data in this map indicate the likely SST for any location in the region during March. This is not an analysis for any particular March. However, the departures between any particular month (since January 1993) and its climatological value are available.
The SST climatology available here was estimated from data measured over the ten-year period 1993 to 2002 (inclusive).
Details of how this climatology was estimated can be obtained by reading the paper:
Uddstrom, M.J.; Oien, N.A. (1999). On the use of high resolution satellite data to describe the spatial and temporal variability of sea surface temperatures in the New Zealand Region. Journal of Geophysical Research (Oceans) 104(C9): 20729–20751.