Sea surface temperature (SST) is retrieved from Geostationary Operational Environmental Satellites (GOES) every hour. A unique feature of this data set is its ability to resolve the diurnal variation of SST. Care must be taken, however, to minimize any possible artifact. At night, the cloud detection is sub-optimal because of the lack of visible data; the atmospheric correction algorithm is different, relying primarily on the 3.9-micron channel instead of the 11-micron channel; and the satellite operation can be unstable from time to time. For these considerations, only daytime SST is recommended for analysis. Results indicate that SST generally remains constant within a few tenth of a degree during a day. At certain season and location, however, it can rise a few degrees during the morning hours in response to solar heating under calm sea state.