Values for the parameters in equation (1) were estimated from the empirical 
distribution of significant heights at Nags Head by the method described in the 
Appendix to give 
Z 1.65 
“(le =" On 198) 
e 
[eee He. | = 3 0.885 (2) 
Equation (2) is shown in the Figure. This distribution function fits the 
empirical distribution at Nags Head better than the comparable models in the 
SPM. Equation (2) can be rearranged to give 
0.606 an( ra |B & ise] Oot22| ae a 
Hee =e 
The assumption that variations relative to monthly mean significant height 
are consistent from month to month was tested at Nags Head by comparing empir- 
ical distributions of significant height by season. Distributions for fall 
(September to November), winter (December to February), and spring (March to 
May) are comparable to the empirical distribution in the Figure. However, the 
distribution for summer (June to August) indicates higher values of H,. than 
the empirical distribution in the Figure at probabilities below about 10 per- 
cent. This discrepancy is due to exceptionally low monthly mean significant 
heights in summer and, in many cases, to nearshore hurricanes. Equation (2) 
seems to be satisfactory for estimating the annual or nonsummer distribution 
of significant height at Nags Head, but the summer distribution must include 
special consideration of hurricane-generated waves at this site. 
V. EXAMPLE PROBLEMS 
kk ek KK KK KK A KOK ® & & EXAMPLE PROBLEM 1 * * * ¥ *¥ ¥ ¥ KKK KK KK XK 
GIVEN: Mean annual significant height of approximately [El = 3.0 feet (0.91 
meter) at Nags Head, North Carolina (see Table). 
FIND: 
(a) The significant height which is equaled or exceeded during 6 
hours every year. 
(b) The significant height which is equaled or exceeded during 1 
hour every year. 
SOLUTION: 
(a) The exceedance percentage Cis > Heel x 100 percent) is 
“ts x 100 = 0.0685 percent 
6 
