Prusa i3 Mk3 - Top layer wrinkles (not on buildplate)
Waves in printed surfaces with FFF are observed at either the bottom layer (common) or the top layer (less common).
Waves in bottom layer
Rippling/wave generation/wrinkling is a common problem for first layer to occur and has a direct relation to the print nozzle to bed distance; a too short of a distance or over-extrusion can lead to this effect. However, this effect is less commonly observed in top layer finishes.  Bottom layer waves are described in more detail in this answer.
Waves in top layer
I have seen this defect before. It is caused by a combination of incorrect hotend temperature and print cooling fan settings. Please reduce the hotend temperature and reduce the fan cooling. The image below clearly shows the differences of such measures.