It is a touch question to be answered as turbulence intensity (TI) varies with time and space in both onshore and offshore. In offshore, the turbulence generating sources in atmospheric boundary layer are various man made structures, hills, mountains, plants etc. Hence, TI varies with the terrains (in flat terrain it is expected to be minimal if convective heat transfer is negligible). In onshore, TI depends on the local coupling between ocean waves and the air layer over the water surface and the presence of islands. Hence, TI is expected to be minimum in the regions where ocean waves and islands are negligible provided convection is minimal. I expect the TI to be more in the offshore compared to onshore.    

You may find some help from the following articles.

http://www.nature.com/nature/journal/v422/n6927/full/nature01382.html

You could also refer to trends of turbulence intensity deduced during experimental works. We carried out some investigation in a wave channel at our lab, for both cases of regular and irregular waves. If interested, try the following link

Article A laboratory study of irregular shoaling waves

Article Experimental study on the hydrodynamics of regular breaking waves