A Technique for Forecasting Storm Waves

Abstract

The forecasting of tidal waves associated with cyclonic storms is a matter of great importance as  these waves cause much devastation and loss of life, aggravating the havoc caused by hurricane force winds and heavy rain. The vast coastline of India is exposed to the ravages of cyclones, especially those originating in the Bay of Bengal. As there is no reliable guide for predicting storm waves for the Indian coastline, a forecasting method has been developed, taking into account the three dimensional topography of a vulnerable section of the eastern coastline.

The technique is based on the evaluation of the relative values of the different parameters that cause storm waves, viz., (i) the astronomical tide, (ii) the 'inverted barometer effect', (iii) the effect of piling up of sea water against the coast by onshore winds of the cyclonic system, (iv) effect of individual waves, and (v) the swell of the forerunners. The third and the fourth of the parameters mentioned above appear to be decisive in producing the total effect. Of these two, again, the former is the more important and depends upon the permanent features of depth distribution close to coast and the distribution of curvature of the coastline itself. Thus, under identical patterns of the wind, certain parts of the coastline would be far more susceptible to de3tructive storm waves than others. On the basis of the study, therefore, it is possible to demarcate permanently, the areas which should be watched and warned with, special care whenever cyclonic storms threaten the coast. This, It appears, could be ,of district assistance despite the well-known ambiguities and difficultie3 in regard to pradiction, of cyclone track, sufficiently in advance.

A few well documented cases of past storm waves have been tested on the basis of the technique proposed. The areas most susceptible to storm-waves have been emphasi8~rl and it is expected that the technique will provide a basis for issuing reliable forecasts of storm surges. Further work is in progress for extending the technique to other belts of the coastline which are occasionally visited by cyclonic storms.