It is actually a single layer ocean model. It uses what are called the shallow water wave equations.

It can be thought of as a grid of resistors capacitors and inductors through which voltages behave flow similarly to water levels. Different capacitances, resistances, and inductivenesses(?) model the changing wave speed and bottom friction to do the depth and bottom friction at each grid cell you are considering. Voltage=water level

By arranging the circuit into the shape of a real world basin and adding voltages that match real world atmospheric forcings you can predict storm surge