Possibly due to upwelling of the cooler water, and/ or rain from pre-Alberto and the other Tropical Waves that have passed through the area.
Upwelling brings the water just below the surface up to the surface. Winds and wind speeds should have some effect also.
I've noticed what seems to be a cooling in the eastern Atlantic about east of 50W. According to the lastest image at oceanweather.com it appears as if water temps between 10N & 20N east of 50W are in the mid 70's or cooler. This is their latest image...
Unfortunately this image will change from day to day but for those of you that see this in the few days after June 19th you will see what I mean. I have also put together an animation that shows the change in temperatures over approximately a month.