armor units of jetties, groins, and breakwaters; scouring around structures; 

 accretion and erosion of beach materials; cutting of new inlets through 

 barrier beaches; and shoaling of navigational channels can often be attributed 

 to storm surge and surface waves. Moreover, surge can increase hazards to 

 navigation, impede vessel traffic, and hamper harbor operations. A knowledge 

 of the increase and decrease in water levels that can be expected during the 

 life of a coastal structure or project is necessary to design structures that 

 will remain functional. 



b. Storms. A storm is an atmospheric disturbance characterized by high 



winds which may or may not be accompanied by precipitation. Two distinctions 

 are made in classifying storms: a storm originating in the tropics is called 

 a tropical storm; a storm resulting from a cold or warm front is called an 

 extratropiedl storm. Both these storms can produce abnormal rises in water 

 level in shallow water near the edge of water bodies. The highest water 

 levels produced along the entire gulf coast and from Cape Cod to the south tip 

 of Florida on the east coast generally result from tropical storms. High 

 water levels are rarely caused by tropical storms on the lower coast of 

 California. Extreme water levels in some enclosed bodies, such as Lake 

 Okeechobee, Florida, can also be caused by a tropical storm. Highest water 

 levels at other coastal locations and most enclosed bodies of water result 

 from extratropical storms. 



A severe tropical storm is called a hurricane when the maximum sustained 

 windspeeds reach 120 kilometers per hour (75 miles per hour or 65 knots). 

 Hurricane winds may reach sustained speeds of more than 240 kilometers per 

 hour (150 miles per hour or 130 knots). Hurricane season lasts from about 

 June to November. Hurricanes, unlike less severe tropical storms, generally 

 are well organized and have a circular wind pattern with winds revolving 

 around a center or eye (not necessarily the geometric center) . The eye is an 

 area of low atmospheric pressure and light winds. Atmospheric pressure and 

 windspeed increase rapidly with distance outward from the eye to a zone of 

 maximum windspeed which may be anywhere from 7 to 110 kilometers (4 to 70 

 statute miles) from the center. From the zone of maximum wind to the 

 periphery of the hurricane, the pressure continues to increase; however, the 

 windspeed decreases. The atmospheric pressure within the eye is the best 

 single index for estimating the surge potential of a hurricane. This pressure 

 is referred to as the central pressure index (CPI). Generally for hurricanes 

 of fixed size, the lower the CPI, the higher the windspeeds. Hurricanes may 

 also be characterized by other important elements, such as the radius of 

 maximum winds R which is an index of the size of the storm, and the speed of 

 forward motion of the storm system V^ . A discussion of the formation, 

 development, and general characteristics of hurricanes is given by Dunn and 

 Miller (1964), Millar (1967), >k:Bride (1981), and Ho et al. (1975). 



Extratropical storms that occur along the northern part of the east coast 

 of the United States accompanied by strong winds blowing from the northeast 

 quadrant are called northeasters. Nearly all destructive northeasters have 

 occurred in the period from November to April. A typical northeaster consists 

 of a single center of low pressure about which the winds revolve, but wind 

 patterns are less symmetrical than those associated with hurricanes. 



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