Extrapolating WW3 data near the shore

[Patrick Reuter]

Hi Grads Fans (like me) !

Using Grads, how could I extrapolate WW3 data from NCEP NOAA near the
coastline? It is 1x1 degree data, but near the coastline the values
are not defined.

For the following reasons: First, I would like to have good-looking
Grads Maps, and second, I want to extract discrete wave heights at
seaside locations.

Note that I am totally aware that wave prediction near the shore
should be simulated -- but here I am just looking for an extrapolation
at neighboring gridpoints (that might even fall on the mainland).

Would you suggest extrapolating the GRIB data directly ? Is there a
tool/command line to do so ? Or does Grids have an "anticipating"
guess how to extrapolate at "undefined" gridpoints (i.e. near the
shore/on the mainland) ?

Any hints are very welcome.

Have a nice weekend
   Patrick