Sea Surface Temperature

A Daily Microwave Optimally Interpolated SST (MW OI SST) is now available:

RSS Active Tropical Cyclones www.remss.com/sst

The MW OI SSTs:

data are derived from microwave radiometer SSTs (AMSR-E, TMI), which can see through clouds.
data provide good temporal resolution, especially important in areas with persistent cloud cover.
data represent night-time minimum, or pre-dawn SST values; diurnal warming has been estimated and removed.
data are gridded at quarter degree (~25 kilometer) resolution.

What is Sea Surface Temperature?

See Characterizing Sea Surface Temperature on the GHRSST-PP site for a good discussion of thermal variability in the upper ocean. The MW OI SSTs can be said to represent pre-dawn temperatures at a depth of ~1 meter, or temperatures just below the diurnal layer.