against the opposing current. Figure 4 documents such wave blocking as described by
Larson and Kraus (2002). Wave blocking is a common occurrence at Shinnecock Inlet
during times of low wave energy.
Occasionally, conditions in the inlet are such that incident waves can propagate into
the throat and break along the western jetty. Waves approaching an opposing current,
such as an ebb current, will steepen, meaning that the wave height increases and the
wavelength decreases relative to the same wave propagating in quiescent water. It turns
out that a wave with longer period can propagate further against an opposing current than
a wave of shorter period. It is wave-steepening that often makes an inlet treacherous to
navigate and why vessels will sometimes wait until ebb tide subsides before entering or
exiting certain inlets, such as the mouth of the Columbia River. In contrast, waves
approaching an inlet on flood tide, representing a "following current," will be reduced in
height and increased in wavelength, making them flat compared to the same waves
propagating on quiescent water. It is intuitively clear that surfing might be promoted by
steeper waves (ebb tide), but the ebb current should not be so strong as to block the
waves.
Average wave conditions along the south shore of Long Island can be characterized
by a significant wave height of about 1 m, with a period between 7 and 8 sec, and
predominantly from the southeast. During hurricanes and large northeast storms, wave
heights can approach 3-4 m with periods ranging from 12-14 sec. Hurricane swells
usually approach from the south. Locally generated wind waves are most common from
the south-southeast to south-southwest, wave heights typically ranging from 1 to 1.5 m
with shorter periods of 5-6 sec.
THREES
As a New York historic surf spot, Threes has been regularly surfed since at least the
early 1960s, and it has been suggested that surfers may have been enjoying these clean-
breaking waves as early as the initial jetty stabilization project in 1953 (Mr. Joe Alber,
Westhampton, New York, a long time local surfer, personal communication). Threes is
one of the few locations where a west or southwest wind blows normal to the crest of the
wave, opposite the direction of wave propagation (offshore wind). Offshore-directed
winds produce a smooth waveform, ideal for surfing. New York lies in the band of the
Westerlies, so the global wind pattern is from west to east. The south shore of Long
Island is also oriented west-southwest to east-northeast (approximately 27 deg north of
east), which means west and southwest winds are side shore (blowing along the wave
crest) or onshore (blowing in the direction of wave propagation) respectively. Southwest
(onshore) wind generates waves that propagate toward the coast of Long Island; however,
these winds create a chaotic sea state. Once the waves are generated, offshore wind,
typically from the northwest, north and northeast, is necessary to organize the sea and
improve surfing potential. Often, wind associated with these large, locally generated
systems does not turn offshore, and the local surfing population is unable to enjoy these
large waves.
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