About surfcast

Waves: the Copernicus North-West Shelf wave model at an open-sea point in each bay; the share of each swell system that each peak's swell window lets through; a breaking height from the slope where the waves break, surveyed where a survey covers it. Wind: the median of up to seven weather models, fewer further ahead (two by the third day, one by the fifth). Tide: harmonics fitted to the Newlyn gauge (scaled and shifted in time for Sennen), and to the St Ives gauge for Gwithian. Checked against the buoys on Now & Hind-cast.

Surfcast

Checks the next three days against your settings and shows the hits and near misses, each with what lines up and what misses. With young kids ticked, each gives the rips, currents, backwash, shorebreak and tide cut-offs in it, with their times where they hold for only part of it, and how fast boards and inflatables drift in an offshore or cross-offshore wind.

Forecast

All four spots at one hour, each part with its confidence. Why takes one peak and hour step by step from the open sea, with every input and its licence.

Maps

Each map's Key explains its marks. The crest lines move the way the waves travel, at three times their pace, on one map at a time: the one most in view. The header's Moving crests button stops them; they stay still, and the button is not shown, where the device asks for reduced motion or a map has found it cannot draw them.

Hit

An hour or more in daylight when every limit of your level holds, and the peak's own tide. Size limits apply to the middle of the faces and sets, so a hit's range can reach past them.

Window

An hour or more in daylight when a peak's own tide, wind and size conditions hold; the same for everyone. The Forecast tab shows them as bars, with the near misses against the same conditions.

Window test

The tide, size and wind a peak's windows are checked against, the same for everyone; the tide from local knowledge.

Each peak's own tide

The tide stages, and sometimes rising or falling, each peak works in, from local knowledge; the same at every level.

Near miss

A run in which, each hour, one condition misses and the rest hold (the faces and sets count as one condition, and so do the wind and its gusts). A miss in a size (faces, sets, wind or gusts) counts only within a small margin. A miss on the tide, shape, wind class, period or consistency counts whatever its size.

Outside your times

Hours outside your chosen times of day; hits and near misses lying wholly in them aren't shown.

Colour

Green meets your settings; light orange is a near miss, with what misses marked. The wind's blue-to-brown names its direction to the beach, not a grade. Nothing else is graded by colour.

Size

Face heights at the peak, in the device's unit.

Faces

The forecast's likely range for the typical breaking face, a 1-in-10 chance either side; in brackets, the sets' top. That is the top of the sets' own likely range; the sets are about the biggest tenth of the waves, as in “6–10 ft (12)”.

Body words

Face heights against an adult's body, from flat to well overhead. The steps, for an adult: flat, ankle, knee, thigh, waist, chest, head, overhead, well overhead.

Swell

Each system in the open sea: its height, period, the direction it comes from, and the share that reaches the peak through its swell window. The wave model splits the sea into the wind sea and up to two swells.

Open sea

The point out at sea where the wave model's numbers are read; each peak's forecast starts there.

Period

Seconds between waves; longer means more power for the height.

Wind sea

Waves still being raised by the local wind, split out by the wave model from the swells.

Swell window

The bearings open to a peak between headlands and islands; the fan on the spot page's map.

% reaches

The share of this swell's energy the peak's swell window lets through, allowing for its spread of directions and period.

Consistency

Steady, sets with lulls, long lulls or inconsistent, from the swell systems.

Steady

Short-period sea: waves come often and the lulls are short.

Sets with lulls

Waves come in groups, sets, with quieter lulls between.

Long lulls

Sets with long lulls between: one long-period swell, or two swells from a similar direction beating.

Inconsistent

Peaky and irregular: seas crossing from two directions, or almost no swell reaching the peak.

Tide

The stage; springs, mid-range or neaps; the zone breaking; the depth over named features from dated surveys. Heights in metres above Ordnance Datum Newlyn.

Quarter, three-quarter

Where the water's height sits between the low and high water around it: low, quarter, mid, three-quarter, high.

Springs, neaps

The day's tidal range: springs the biggest, near a full or new moon; neaps the smallest; mid-range between.

ODN

Ordnance Datum Newlyn, the land-survey zero near mean sea level; tide heights here are measured from it.

Wind

The median of several weather models at 10 m, in knots, classed by its angle from straight offshore at each stretch of beach: offshore (off) within 30°, cross-offshore (x-off) to 67.5°, cross-shore (cross) to 112.5°, cross-onshore (x-on) to 150°, onshore (on) beyond. Also the gusts, the models' spread, the surface and any sea breeze.

Off, x-off, cross, x-on, on

Wind's angle to the beach: off blows land to sea, on sea to beach, cross along it; x-off, x-on between.

kn

Knots: 1 kn is about 1.9 km/h.

Shape

Spilling, plunging, dumping, closeout-prone or surging, from the beach's rules by tide stage and its surveyed slope, moved one step by a wind of 8 kn or more (offshore towards plunging, onshore towards spilling); a dash means no rule yet, or no surf. Where the slope is surveyed, the basis gives the surf similarity (under Method).

Spilling

Whitewater tumbles down the face from the top.

Plunging

The lip throws forward and the wave breaks hollow.

Dumping

Plunges hard straight onto shallow sand, often at the shore of a steep beach.

Closeout-prone

The whole wave tends to break at once along its length. Written “closeouts” where space is short (the Forecast rows, the strips, the map labels).

Surging

Rides up a steep beach without properly breaking.

Currents

Rips, streams, backwash, shorebreak, tide cut-offs, board drift; timed where they hold for part of a hit or near miss. Each peak's fixed features and when they are active come from local knowledge.

Rip

A narrow current running out from the shore through the surf.

Tidal stream

Water moving along the coast with the tide, beyond the surf.

Boundary current

A current running along a headland or rocks at the side of a beach.

Ebb jet

Water flowing out of an estuary mouth as the tide falls.

Backwash

Water running back down the beach after each wave; forecast at three-quarter and high tide, stronger on steep beaches.

Shorebreak

Waves breaking right at the water's edge, onto the sand.

Tide cut-off

Where the rising tide covers ledges, or the way along the beach between coves.

Board drift

Boards and inflatables afloat drift at about 3–6% of an offshore or cross-offshore wind of 10 kn or more.

Confidence

High, medium or low per axis, from lead time, model agreement, buoy and log checks, survey age and missing inputs. Also the open-sea point's depth, a swell near the window's edge, the tide's gauge and the model runs' age; Why gives each hour's reasons. On the Forecast tab, conf is the lowest of size, wind, shape and tide.

Every size carries its peak's label, which follows the evidence behind it:

learning

Not yet verified at this peak: sizes likely read about one body-scale step high (chest where waist is nearer). Sizes come from the swell window, the wave physics and desk values for the beach until Charlotte's first session sets the face scale.

calibrated

Verified against a live buoy in this peak's swell window, or against at least 30 logged sessions here.

modelled

From a local wave model that has passed its checks at this peak.

Ratio peak

No forecast of its own: another peak's faces scaled for the swell reaching here. “Godrevy ×1.2” means faces about 1.2 times the Gwithian car park's, for the day's swell direction; how the ratio is made is under Method.

Now & Hind-cast

Each buoy's readings over the last 72 hours beside our forecast as issued and the open-sea model B1 (GFS-Wave, as apps such as Windy show).

Hs

About the mean height of the highest third of waves, trough to crest; the significant wave height. As the buoys and the wave models give it, in metres; not a face height.

B1

NOAA's GFS-Wave forecast at the model cell nearest the buoy, as apps such as Windy show; a baseline for ours.

Waverider

A wave buoy measuring height, period and direction; readings on Now & Hind-cast.

Log

For the household, signed in once per device with its code. You log what you saw before any forecast shows; logs go to the household's database, never into the public forecast.

• UK time (GMT or BST), 24-hour clock. Directions in degrees true, where the swell or wind comes from.
• The latest forecast and buoy readings are kept on the phone. With no signal, or when the network is too slow, the page shows the saved copy and says so.

3h

Hourly to 72 hours ahead, then one hour in three to seven days.

First and last light

Civil dawn and dusk, the sun 6° below the horizon; hits and windows count only between them.

Run, waves

Run: when this forecast was made. Waves: when the wave model behind it ran, and its age. Both are in the header.

Stale since

The forecast shown was made over 12 hours ago; no newer run has loaded.

surfcast is a personal, non-commercial forecast.