Persistence of Wave Heights 
6. Table B5 shows the number of times in 1991 when the specified wave 
height was equaled or exceeded at least once during each day for the duration 
(consecutive days). Data for 1980 through 1991 are averaged and given in 
Table B6. An example is shown below: 
Height Consecutive Day(s) or Longer 
ie | ge eG nian OT Gy AN) Epo as skye «Ske Gh eas 
0.5 18 15 14 13 12 11. 10 9 8 
1.0 50 34 24 21 18 14 12 8 7 3 2 
1.5 “Ml WO & 6G 2 1 
2.0 22) 95 wal 
2.5 10 52 
3.0 6 1 
3.5 1 
4.0 1 
This example indicates that wave heights equaled or exceeded 1.0 m 50 times 
for at least 1 day; 34 times for at least 2 days; 24 times for at least 
3 days, etc. Therefore, on 16 occasions the height equaled or exceeded 1.0 m 
for 1 day exactly (50 - 34 = 16); on 10 occasions for 2 days; on 3 occasions 
for 3 days, etc. Note that the height exceeded 1 m 50 times for 1 day or 
longer, while heights exceeded 0.5 m only 18 times for this same duration. 
This change in durations occurred because the longer durations of lower waves 
may be interspersed with shorter, but more frequent, intervals of higher 
waves. For example, one of the times that the wave heights exceeded 0.5 m for 
16 days may have represented three times the height exceeded 1 m for shorter 
durations. 
Spectra 
7. Monthly spectra for the offshore Waverider buoy (Gage 630) are 
presented in Figure B8. The plots show "relative" energy density as a 
function of wave frequency. These figures summarize the large number of 
spectra for each month. The figures emphasize the higher energy density 
associated with storms, as well as the general shifts in energy density to 
different frequencies. As used here, "relative" indicates the spectra have 
been smoothed by the three-dimensional surface drawing routine. Consequently, 
extremely high- and low-energy density values are modified to produce a smooth 
surface. The figures are not intended for quantitative measurements; however, 
B2 
