Hour — local time at the break, like every
time on this page.
Rating — how good the surf should be at
this hour, from 0 to 5 stars: the swell's size, its period and how well its
direction fits this break, reduced by the wind, the tide and a crossing second
swell. Half stars round down.
Verdict — the word for the star band:
poor under 2, fair 2 to 3, good 3 to 4, epic 4 and over. A break whose shoreline
has not been surveyed is unrated, never scored low.
Wave height — the significant height of
the sea at this hour, the typical larger waves in open water, not the face at
the beach.
Period — the seconds between the waves
carrying most of the energy. At the same height, a longer period carries more
power.
Swell direction — the compass
direction the swell comes from, which the rating compares with the directions
that reach this break.
Swell trains — the model splits the sea
into up to three swells; their heights, largest first. One figure means one
train, a reading and not a gap.
Tide — the predicted height of the water
about mean sea level, and whether it is rising or falling, from EOT20.
Wind — measured against this break's
own shoreline: offshore blows from the land and grooms the wave, onshore blows
in from the sea, cross sits between; glassy is almost no wind.
Gust — the strongest gust the atmospheric
model expects at this hour. A gust well above the steady wind means a surface
that keeps changing.
Sky and air — the sky at this hour and the
air two metres above the ground. The air is not the water temperature.
Rain — how hard it rains at this hour, in
millimetres per hour: a rate, not a chance of rain. Under 0.2 mm/h is not
printed.
Power — the wave power at this hour, in
kJ per metre of wave crest, from the height squared and the period: what
separates two hours of the same height.
Not forecast this far out — the sky, the
air, the rain and the gust come from the atmospheric model, which stops at ten
days. The sea, the wind, the tide and the rating carry on.
Burning Swell
Birsay Bay