An Evaluation of Operational Wave Forecasts on Shallow Water
The KNMI wave model gono (Sanders, 1976) with its shallow water extension is in operational use for the forecasting of wave conditions in the southern North Sea. The model uses a parameterized spectrum for the calculation of windsea supplemented by empirical growth laws. Swell is calculated following an idea of Haug (1968). gono has been verified during the last two winters, against wave data from several positions. Also, during the winter 1979/80 a comparison was made with the model of Golding (1978) which is operational at the British Meteorological Office. After a brief discussion of gono and the quality of the observational data, we will give the results of the comparison. The comparison is made for the significant wave height, Hs, and for Hs,10, which is the significant wave height derived from wave energy in waves with a period greater than 10 s. This latter quantity is important for the navigation of very large crude carriers entering Rotterdam harbor and for the construction of the Oosterschelde storm surge barrier. Also, calculated and observed winds are compared. The comparison is made for analyzed wind data as well as 12- and 24-h forecasts. First, we discuss the time series, with emphasis on interesting events, such as the extreme swell (T≃ 18 s) occurring on January 15,1980, which was generated at very northerly latitude, and the extreme situation on April 19–20,1980, when a northerly storm of very long fetch generated waves with Hs 5–7 m on shallow water. Further, we present results of a statistical analysis, including scatter plots and monthly summary tables giving for wind direction, wind velocity, H s, and H s,10 the number of observations, the average of the observed values, the average error, rms error, number of cases overpredicted, and number of cases underpredicted. Also, the scatter index (ratio of standard deviation and average observed value) is given. Values range from 20 to 35%, depending mainly on the quality of wind calculations.
KeywordsShallow Water Significant Wave Height Time Series Plot Scatter Index Wave Forecast
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