In the southwestern North Atlantic Ocean, the area between the 80F isotherm and the equator, and between 30W longitude and the western most land boundary, is compiled for each month from a world atlas of sea surface temperatures. Between February and March, the area starts to increase from 100 units until a maximum of over 1000 units is reached in August, after which the area decreases. One unit equals one latitude/longitude square. While increasing by swelling to the north, the temperature inside the area essentially does not increase, in spite of the self-evident fact that absorption of solar heat increases the whole time in the top 100 m of the water column. It is proposed that sea level rises by thermal expansion, starting at the equator, producing a northward slope in sea level which in turn drives warm water in the surface layer northward. This proposition is consistent with the heat balance required of the North Atlantic.