Recent tests of all generations of numerical wave models indicate that extr
eme wave heights are significantly underpredicted by these models. This beh
avior is consistent with the finding by Ewing and Laing that fully develope
d wave spectra do not have the universal self-similar form postulated by Pi
erson and Moskowitz. This paper postulates that it is inappropriate to scal
e fully developed seas by winds taken from a fixed level above the mean sea
surface. Instead, winds should be taken from a dynamically scaled height t
hat is linearly related to the wavelength of the spectral peak. This altern
ative scaling is consistent with friction-velocity scaling and yields predi
cted wave heights and periods that are in better agreement with the data co
llected by Ewing and Laing and appear to explain some of the discrepencies
in results from previous studies with numerical wave models in large storms
.