There is no course textbook but some useful and relevant texts are listed below.

Buy at Amazon Durran, Dale R. Numerical Methods for Wave Equations in Geophysical Fluid Dynamics (Texts in Applied Mathematics Series, Vol. 32). New York, NY: Springer, 1998. ISBN: 9780387983769.

Buy at Amazon Haidvogel, Dale B. and Aike Beckmann. Numerical Ocean Circulation Modeling. River Edge, NJ: World Scientific Publishing Co., 1999. ISBN: 9781860941146.

Buy at Amazon Haltiner, George J., and Roger T. Williams. Numerical Prediction and Dynamic Meteorology, 2nd Ed. Hoboken, NJ: John Wiley & Sons, 1980. ISBN: 9780471059714.

Buy at Amazon Jacobson, Mark Z. Fundamentals of Atmospheric Modeling. Cambridge, MA: Cambridge University Press, 1998. ISBN: 9780521637176.

Buy at Amazon Kantha, Lakshmi H. Numerical Models of Oceans and Oceanic Processes. Academic Press; 1 edition, 2000. ISBN: 9780124340688.

Buy at Amazon Pedlosky, Joseph. Ocean Circulation Theory. New York, NY: Springer; 1st ed. Corr. 2nd printing edition, 2004. ISBN: 9783540604891.

A handy quick-reference for some methods is Numerical Recipes on-line.