Tidy up the verbose statements and remove unnecessary bits of code.
Fix the way the extrapolation of data onto land (from the HYCOM grid perspective) happens. Previously, the land mask was used to check the position, but I have realised this is unnecessary as the interpolation only gives NaNs if the boundary falls on land. So, I have simplified the check to only trigger the extrapolation to occur if the layer being interpolated is the FVCOM surface layer. This is because we always want a value for every node, even if there is only one. The vertical interpolation will repeat the surface value to all FVCOM depths in that case. I see no other way of handling this if we have an open boundary node which is shallower than the second shallowest HYCOM layer.