An area of the ocean surface which is experiencing warmer sea surface temperatures (ssts) than the typical maximum temperature reached at that location. The typical maximum temperature, which generally occurs in late summer, is important because this is the highest temperature to which corals in a particular location are accustomed. So, when the SST exceeds this by some threshold (typically one degree C) corals are in danger of bleaching. Many factors such as salinity, insolation, winds, and local currents play a role in coral reef bleaching, but clearly extreme ssts are a critical factor; also called "hotspots".