b. Wind and wave hlndcast data for the extratroplcal storms of 

 April 1956 and March 1962 were available from the Coastal Engi- 

 neering Research Center's Sea State Engineering and Analysis 

 System (SEAS) (McAneny 1986). Appropriate values of wind and 

 wave parameters were extracted from the SEAS data base. These 

 estimates were then transformed into boundary forcing functions 

 for the wave model. 



c. The extratroplcal storm of April 1978 is too recent for inclu- 

 sion in the SEAS data base which currently spans the period 

 1956 to 1975. Therefore, a supplementary analysis was re- 

 quired. Surface pressure maps were digitized, and wind fields 

 were computed using the atmospheric boundary layer model deve- 

 loped for CERC's Wave Information Studies (WIS). Previous 

 applications of the WIS wind model form the basis of the hind- 

 cast results available in SEAS. The computed winds were 

 applied as forcing functions to the wave spectral transforma- 

 tion model. 



14. All wind wave computations were made with the WIS discrete spectral 

 wave growth transformation model (Hughes and Jensen 1986) . This model pre- 

 dicts the frequency and directional transformation of forced wind waves in 

 deep, intermediate, and shallow water. A sequence of three nested, coupled 

 computational grids was used to bring the hindcast results to a point approx- 

 imately 12 nautical miles east of the Virginia Beach area, at longitude 

 75°45'W and latitude Se'SO'N. Mean water depth at this location is 11 m. The 

 frequency spectra of sea surface variance for the times of maximum wave height 

 at this location are depicted in Figure 4 for both hurricanes and extra- 

 tropical storms. A summary of the hindcast peak wave characteristics is in 

 Table 3. 



15. The hindcast for the April 1978 storm was compared to gage measure- 

 ments at CERC's Field Research Facility, at Duck, North Carolina. The range 

 of wave heights and periods hindcast compared well with gage data in about 



10 m of water. 



16. Of the hurricanes, the August 1933 storm was by far the most severe 

 due to its passage in an onshore direction just to the south of the study 

 area. The storm produced the highest swl of record (record length being 50 to 

 60 years) with a maximum projected surge of +8.7 NGVD for Virginia Beach and 

 the highest significant wave. The March 1962 extratroplcal storm is one of 

 the most severe storms of this class to affect the mid-Atlantic coast. Wave 

 heights of 10 to 12 m were hindcast in deep water beyond the continental 

 shelf. The largest component of the waves was high energy swell propagating 

 across the shelf to Virginia Beach. For these reasons the August 1933 



13 



