PART II: HINDCAST EXTREMAL ANALYSIS 



Hindcast Data Selection 



5. The hindcast wave data set used in this study was provided on mag- 

 netic tape by WIS. The data consisted of one record of wave climate charac- 

 teristics including significant wave height, period, and direction for every 

 3 hr for the years from 1956 to 1975 for a total of approximately 58,400 rec- 

 ords (Ragsdale 1983). A computer program was developed to search this tape 

 for records having specific directions and magnitudes. The program writes 

 tabular listings of the selected data records for further data reduction. 

 The WIS grid point (Point 17) that is nearest to the Chiniak Bay area is 



120 nautical miles east of Kodiak (see Figure 2). Events producing signif- 

 icant wave heights of 6 m or more were chosen and maximum significant wave 

 height and associated period were then selected for each event. Appendix A 

 provides a listing of the 78 resulting maximum significant wave heights, 

 each with its date of occurrence and period. The choice of 6 m as a selec- 

 tion criterion was arbitrary. However, the choice was modified and vali- 

 dated in terras of the resulting extremal analysis. The data were surveyed 

 for significant storm events with wave directions corresponding to a direc- 

 tion window defined by Cape Chiniak to the south and Long Island to the north. 

 This window was taken to be approximately 95 to 140 degrees relative to True 

 North for waves traveling from the north and 90 degrees for waves from the 

 east. The direction window was constructed using the approximate center of 

 the St. Paul Harbor area (a little to the northwest of Puffin Island) as the 

 vertex of a triangle with the other two vertices defined by Cape Chiniak and 

 Long Island. 



Probability Distribution for the 

 Number of Storms per Year 



6. The number of storms per year producing significant wave heights of 

 6 m or more is listed in Table 1. Note that for 1957 there was no event pro- 

 ducing significant wave heights of 6 m or more; whereas 1963, 1968, and 1969 

 each produced seven such events. The number of storms per year is listed with 

 its observed frequencies in Table 2. A common assumption for studies of this 

 type is that the number of storms per time interval is distributed according 



