About surfcast

• The Surfcast tab, the home page, checks the next three days against the settings you choose: your level, the times of day you can go (morning until 12:00, afternoon 12:00 to 17:00, evening from 17:00) and whether young kids are coming. They stay on this device and fold into one line at the top once chosen; tap it to change them.
• A hit is a run of an hour or more in daylight when every limit of your level holds, and the peak's own tide as well (each card lists its peaks' tides). A near miss is a run when all but one hold and that one misses by only a little: the settings give the margin, the same at every level, and a miss on the tide or the shape counts whatever its size. A level's size limits are for the middle of the forecast faces, so the range a hit lists can reach past them. The levels' limits are starting values, to be confirmed with Charlotte.
• The slider runs over the three days, a row for each location: a green bar for each hit and a muted green one for each near miss, drawn only in the times of day you chose. Below it, a card for each location with at least one: its map at the slider's hour, its peaks then, and each hit and near miss with its times, what lines up, and what opens and ends it or what misses and by how much. The one the slider is in is outlined; tap another to move the slider to it. A location with none has one line.
• Green means only that the forecast meets your settings. The locations stay in the same order and nothing is ranked. With young kids ticked, each hit and near miss adds a line for the currents in it (active rips, backwash, offshore drift and a dumping shorebreak) with their times.

• The Forecast tab gives each part of the picture with how sure it is and why, round one time control over the day: the hour, large, with the tide at it in words, over the day's tide curves with night and twilight shaded. Drag it, tap it or use the arrow keys; it snaps to the hours the forecast has (hourly to 72 hours, then 3-hourly) and stays at the top of the screen as the page scrolls. Everything below it is at that hour.
• Tide and light come once for all four spots: spots whose high and low waters fall within ten minutes of each other share a row (and a solid curve on the chart), and St Ives Bay (Gwithian), about half an hour later than Mount's Bay, has its own (dashed).
• Under them, each peak's windows and near misses on the day are bands on the same time axis: a window (a run of an hour or more when every one of the peak's conditions holds) has a solid outline, a near miss (all but one hold, and that one misses by only a little, as on the Surfcast tab) a dashed one, named by what misses. Tap a band for its sentence and a way to its hours.
• Every size has its peak's label. While every peak shares one, a single line above the sizes says so; a peak whose label differs carries its own beside its sizes.
• The four locations follow, always in the same order: Gwithian, Sennen, Praa Sands, Long Rock. Each has a small map beside its peaks. The list runs in the order the dots run on the map (top to bottom, or west to east along a beach facing south). A peak with its own forecast gives its name with a sparkline of its typical faces through the day, its faces at the hour in feet (typical range, the top of the sets in brackets) with body words, then its shape, the wind (its class to the beach and knots) and the confidence. A ratio peak gives its faces. Tap a peak, on the list or the map, for everything at that hour and a link to its why chain.
• The maps draw the sea at the model cells as arrows, the way the waves travel, their length the open sea's height in metres (not a face); the wind at each stretch of beach as a coloured arrow (the colour is its angle to the beach, not a grade); and the peaks as dots (their own forecast) or rings (a ratio). Under each map, the sea at the bay cell every forecast there starts from, one line a system, greyed where it reaches none of the peaks. The key under each map explains the arrows at the map's own scale.

• A spot's day has the same time control, with the spot's own tide, its tide and light and its peaks' bands. Its map takes the screen's width, with three extents: the peaks close in, the bay, and the approach out to the coarser GFS-Wave cells (outside the coast data the map is hatched). Then each peak at the hour, the peaks' strips through the day (typical faces with the top of the sets, the wind by hour in knots, the shape), and, folded, the beach: its fixed currents and features, the banks' survey and how old each input is.
• Why takes one peak and hour from the offshore sea to the faces, tide, shape and wind, then says what to watch, what would change it, how sure each axis is and why, and what the hour holds beyond that chain (the sets, the spread between the wind models, the depth over named features, the currents with their features' words), with every input of the run by source, its run time and licence.

• Now & Hind-cast puts each buoy's readings over the last 72 hours beside two forecasts for the same place: ours as it was issued, and the open-sea model (B1: GFS-Wave at the nearest open-sea cell, what apps such as Windy show). Both run on for the next 24 hours.
• How to read the charts (the keys, what the heights are, how our forecast is drawn and what every buoy shares) is said once on that tab, above the buoys; under each buoy are its own sources and every value in a table.

• Logging is for the household: each device signs in once with the household code, and the log links appear on the Forecast tab's peak sheets, a spot's day and Why. The forecast itself needs no login.
• A log asks for the sets and the typical faces on the body scale before it shows any forecast value, then the shape, the wind as it felt and the surface, with optional notes. After saving, it shows what the forecast said for that peak and hour beside what was logged. A quick “looked, didn't surf” takes a time and the two sizes.
• Logs wait on the phone without a signal and send when it has one. They go to the household's database, never into the public forecast.

Size

Face heights at the peak as a range from the 10th to the 90th percentile: typical faces, the sets, and on Why the biggest in about 20 minutes. Feet by default, metres with the ft/m switch. The body-scale words are for an adult: flat, ankle, knee, thigh, waist, chest, head, overhead, well overhead.

Swell

Each swell system at the reference cell (height, period and the direction it comes from) and the share of it that reaches the peak through its swell window. A short wind sea is shown as wind sea, never as swell. The swell and the second swell are ranked by height each hour, so they swap places when one system overtakes the other.

Consistency

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

Tide

The stage by height between the low and high water around it: low, quarter (¼), mid, three-quarter (¾) or high; springs, mid-range or neaps; which zone is breaking; and the depth over named features from dated surveys. Levels are metres above Ordnance Datum Newlyn.

Wind

The median of several weather models at 10 m, in knots, classed against the shore at that section: offshore (off), cross-offshore (x-off), cross-shore (cross), cross-onshore (x-on) or onshore (on). Also the gusts, the spread between models, the surface it leaves and any sea breeze.

Shape

Spilling, plunging, dumping, closeout-prone or surging, from the beach's local rules by tide stage and the surveyed slope where the waves break. A dash means no rule covers that stage yet, or there is no surf. Where a survey gives the slope, the basis also gives the surf similarity: the beach's slope against the steepness of the breaking waves (the Iribarren number). Under about 0.4 waves tend to spill, from about 0.4 to 2 to plunge, and above about 2 to surge; a steep beach near high water gives higher values.

Currents

The peak's fixed features (boundary rips, streams, backwash off rocks) and when they are active; backwash near high water, stronger on a steep beach, with bigger waves and at a higher surf similarity; and the drift of anything floating when the wind is offshore or cross-offshore at 10 kn or more.

Every hour carries a confidence band (high, medium or low) for each of size, wind, shape and tide, each with its reason. The single word on the Forecast tab is the weakest of the four. A watch item names a buoy reading that would bear the forecast out, and “would change it” says what would move it, such as a swell direction a few degrees either way.

Every size sits beside its peak's label, which follows the evidence behind it.

learning

Not yet verified at this peak: sizes come from the swell window, the wave physics and desk values for the beach, on a face scale that is set at Charlotte's first session.

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.

Each peak also has a tier: the method behind its forecast. Every peak starts at tier 0: the wave model at a cell in the bay, the share of each swell system that the peak's swell window lets through, and a breaker height from the beach's slope, with the beach's own rules for shape. Tiers 1 to 3 are later methods: a correction learned from the buoys, then a wave model of the bay and its surf zone, then corrections learned from logged sessions. A peak moves up a tier only after the new method has scored better against the buoys and no worse against the logs. The label follows the evidence behind the sizes, not the tier.

Until Charlotte's first session sets the face scale, sizes read about one body-scale band high: chest where waist is nearer, for example.

The other peaks show as a ratio to a parent peak for the day's swell direction: “Godrevy ×1.2” means faces about 1.2 times those at the Gwithian car park. They get their own forecast once logs or a local wave model support one.

Each hour's ratio is the product of two parts, both shown. The “sector ratio” is the size relative to the parent for swell from that direction, from what is known locally, to be checked against what people see there (×1.0 where none is set yet). The “gate” is the change the swell windows make within that direction: below 1 when something screens this peak but not its parent, such as the Stones and Godrevy Island at Godrevy in north-westerly swell.

• Times are UK time (GMT or BST) on the 24-hour clock. Directions are degrees true, the direction the swell or wind comes from.
• Hourly to 72 hours ahead, then 3-hourly to seven days (marked “3h”).
• The header gives the time of the forecast run and its age, and the wave model run behind it. After 12 hours it reads “stale since” the run time.
• The app keeps the latest forecast and buoy readings on the phone. With no signal, or when the network is too slow, it shows the saved copy and says so.