The peak period identifies either the
period (the time between waves) associated with the locally generated wind sea (in cases
with strong local winds) or the dominant wave system (swell) that is
generated elsewhere. Note that this peak period field shows discontinuities.
These discontinuities can loosely be interpreted as swell fronts, although
in reality many swell systems overlap at most locations and times.
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www.nws.noaa.gov 
