With unstructured grids, lon and lat are not dimensions, but are 1-d variables specifying the lon,lat of each "column" of the unstructured grid.

Add to your existing ncl scripts, code such as:

lat1d = f[0]->lat

lon1d = f[0]->lon

res@sfXArray = lon1d

res@sfYArray = lat1d

Plotting unstructured grids with MATLAB

This matlab routine shows how to plot results on an unstructured grid.

Regrid output to regular grid

Another option for looking at the unstructured grid is to interpolate to a uniform grid (something finer than the finest resolution of your variable grid is recommended), and then use your standard plotting routines.