Simplified spectral forecasts of sea and swell waves by graphical means

Abstract

The spectral method of sea and swell wave forecasting yields more meaningful results than do other forecasting methods. To shorten the time required to make such a forecast the authors used high-speed computer methods and the Piers on-Neumann-James spectra to make spectral forecasts and display the results in graphic form for several synoptic weather models and a wide range of wind and fetch speeds. Forecasts were completed for a stationary fetch model, a fetch moving to leeward and a fetch moving to windward . Computations were made with the assumptions that a rectangular generating area could be delineated; that a spatially-uniform mean wind existed; that this wind did not increase or decrease until the time of forecast; and finally that if the fetch were moving, its movement was steady. The following parameter limits were established: a. wind speeds, 15 to 55 knots; b. speed of the generating area, 15 knots to and including the wind speed ; c. forecast times, 6 to 72 hours. Results of the forecasts are plotted on approximately 250 graphs which show the geographic distribution of spectral sea or swell components relative to the fetch at forecast times.