Marin County

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 (a longer period counts as bigger), its period and how well its direction fits this break, reduced by the wind, the tide and a crossing second swell; above the size this break works up to the stars fall, to none where it closes out. 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, or too big, whatever the stars, when the swell is beyond what this break or your level can take. 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 above MLLW, and whether it is rising or falling, from NOAA.

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.

Air — the air two metres above the ground. With a wave model picked whose centre runs an air model it is that model’s; otherwise the middle of the air models that reach this hour. Past ten days the sky is not forecast, so the air stands without it.

Sea — the sea-surface temperature. With a wave model picked whose centre runs a sea model it is that model’s; otherwise the middle of the sea models that reach this hour, and where none does, the dated OISST analysis. A forecast, like every other figure here.

Models for the air and the sea — how many models the air comes from, and whether they agree: within 3° they agree, wider apart they are split. With one model left, or one picked in the model menu, there is nothing to compare, so agreement is not measured.

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.