A hindcast study of the extreme wave climate of offshore west Africa (WAX)
This paper describes the methodology and selected results of a Joint Industry Project called WAX (West Africa Extremes) whose purpose was to develop estimates of extreme waves for the West Coast of Africa between 5 N and 15 S. Extreme waves there consist of swell propagated from distant sources associated with extratropical storms in deep southern latitudes or from episodic enhancements of anticyclonic southeast winds off South Africa. The basic steps of the hindcast method are described: storm selection, specification of wind fields, application of a directional spectral wave prediction model, model validation and external analysis of results of hindcasts of the historical storm population selected. The validation consisted of a comparison of wave model predictions and measurements of significant wave height, peak spectral period and frequency spectra during several episodes of extreme swell conditions, selected from wave measurements recorded at a platform offshore Nigeria over a two-year period (1981--82) and over a 12-month period (1990--91) by a Waverider buoy moored offshore Cabinda. It was found that despite the special difficulties of hindcasting the wind fields of Southern Hemisphere (SH) storms caused by sparsity of meteorological data, the hindcast skill exhibited in these comparisons is comparable with the good agreement typically achieved in Northern Hemisphere (NH) basins with the hindcast methodology applied. The wave model used for these hindcasts has been well validated in NH basins mainly in extreme storm regimes where the source terms which model the physical mechanisms of wave growth and dissipation dominate the model solution. The WAX extremes are derived from hindcasts of a population of 50 historical storms. The extremes are summarized for selected areas.
- OSTI ID:
- 136649
- Report Number(s):
- CONF-950501--
- Country of Publication:
- United States
- Language:
- English
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