This paper describes a new class of summertime subtropical sea surface temperature (SST) anomalies that have basin scale, amplitudes up to 3¿C and duration of up to 2 weeks. These have been discovered in the Microwave Imager (TMI) SST analyses. One-dimensional physics and numerical weather prediction operational air-sea fluxes are able to reproduce many aspects of the observations. The mechanism of creation of these summertime anomalies depends on the formation of shallow ocean mixed layer depths. Their persistence is controlled primarily by the duration of appropriate atmospheric conditions. Model studies also suggest that near synoptic scale surface flux variations, of the type considered here, cause significant warming of SST over monthly to seasonal timescales.