Section II. ON PREDICTION OF STORM SURGE 



1. General 



When a basin of water, such as a sea, lake, bay or estuary is dis- 

 turbed by some forcing mechanism, there will be a transient motion to at 

 least a portion of the water contained in the system. This sort of fluid 

 motion is referred to as a surge^ and can produce large variations of the 

 water surface, especially in the shallower regions of the basin. Among 

 the known mechanisms that cause surges are submarine earthquakes which 

 generate tsunamis, a large mass of earth sliding into the water, edge 

 waves, and storms. Here we shall be concerned with tropical storms, and 

 generally with emphasis placed on the surges associated with a hurricane. 



The name, hurricane, applies to migratory cyclones which originate 

 in the tropical regions over the oceans near the equatorial zone. Such 

 storms are referred to by different names throughout the world, although 

 their origin, structure, and behavior are essentially the same. A hwcvi- 

 aane is called a typhoon in much of the Pacific Ocean, a tvopiaal cyclone 

 in the Bay of Bengal and the Arabian Sea, and a willy-willy off the coasts 

 of Australia. A tropical storm is said to become a fully developed hur- 

 ricane when the maximum wind speed equals 75 miles per hour (65 knots) 

 or more than 12 on the Beaufort scale of wind force. A hurricane is 

 essentially a heat engine, thus implying the existence of a heat source 

 and a cold source. Its development, intensification and dissipation has 

 yet to be fully understood, although considerable knowledge has been 

 gained in our present century. It is beyond the scope of this paper to 

 present the known complex mechanisms which govern the hurricane; however, 

 we will mention some of the elementary characteristics primarily from 

 the standpoint of those related to the induced surge. 



Because of the direction of earth's rotation, the hurricane has a 

 cyclonic wind circulation which is counterclockwise in the Northern 

 Hemisphere and clockwise in the Southern Hemisphere. The wind system 

 just above the water surface is circular, having an average diameter 

 of about 400 miles across to the gale winds of 40 miles per hour and 

 approximately 100-mile diameter to the hurricane force winds. Moreover, 

 the wind system extends upward in a dome-like configuration to a maximum 

 elevation of about 6 miles or more. 



At the center of wind rotation and just above the surface is a 

 region of relative calm called the eye of the hurricane which extends 

 vertically upward through the wind system dome. The eye is cicular or 

 elliptical depending on the characteristics of the hurricane, has an 

 average diameter of about 14 miles, but may vary from about 4 miles to 

 25 miles (Dunn and Miller, 1964). Atmospheric pressure near the sur- 

 face of the ocean is minimum in the eye and usually increases in all 

 directions to the storm's periphery. The temperature in the eye is 

 higher than its surroundings, principally at lower levels, which causes 

 the air to rise vertically, thus allowing air from the adjacent wind 



