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5 Wave Evolution in Non-uniform Currents in Deep Water
Fig. 5.30. Synoptic charts of the southern Indian Ocean on April 26 (a) and
April 27 (b), 1985
presented long gentle swell waves arriving from southern latitudes. They were
generated by the south-westerly wind acting at a fetch of about 1200 miles
long within not less than a 24 hour period of time. The wave height must
have been increased under the influence of the opposite Agulhas Current. As
a result of two superimposed wave systems, the height of individual waves
could be significantly increased, especially at the time when the swell and
wind wave coincided by phase. Thus, under these conditions, some waves of
large height might have occurred at some moment. However, the phenomenon
of abnormal waves cannot be explained from the point of view of a linear wave
superposition. In particular, it is impossible to explain the wave shape, its
asymmetrical profile with a long deep trough, the "hole in the sea" situated
in front of the high steep crest and its sudden appearance.
At present, due to the absence of theory and field measurements, it is
practically impossible to forecast abnormal waves. However, on the basis