THE HURRICANE SURGE

D. Lee Harris

Abstract


The landfall of a hurricane is generally accompanied by an increase in the tide level by four to fifteen feet above the normal value for the time and place at which the storm crosses the shoreline. This difference between the observed tide and that predicted from astronomical considerations is called the storm surge. The hydrodynamic theory of these disturbances has not been worked out in sufficient detail to permit a satisfactory theoretical approach to the storm surge prediction problem. Hence, the best guide to the probable behavior of future hurricane surges is believed to be the study of the effects of past hurricanes on sea level.

A gradual rise in tide level above predicted values may begin more than 24 hours before the storm makes its nearest approach to the station. Occasionally, the tide falls below normal for many hours during the approach of the storm. A rapid rise generally begins about the time gale winds associated with the hurricane are first experienced. The peak surge at any location along the shore usually occurs within an hour or two after the nearest approach of the storm to the station. The maximum surge generally occurs somewhat to the right of the storm track, and the zone of extremely high water usually extends further to the right than to the left of the storm track. The fall in water level after the storm is more rapid than the rise in areas with good drainage, but in marshland a week or more may be required for the water level to return to normal.

The maximum height of the storm surge along the open coast is clearly a function of the storm intensity, but this factor alone is not sufficient to explain more than half of the observed variance in the reported peak storm tides. Topographic effects, such as the funneling of water in converging bays can alter the amplitude of the surge by a factor of two in a distance of only a few miles. This fact, together with the tendency of severe hurricanes to destroy the tide gages near their centers, and the difficulty of eliminating the effects of surface wind waves in interpreting high water marks, make it difficult to determine exactly the nature of past storm surges.

Keywords


storm surge; storm tide; hydrodynamic theory

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