Arugam Bay, Sri Lanka · Asia/Colombo
Arugam Bay
Pointing right at the open Indian Ocean. South-west monsoon is the season. No tide station in range, so the app says so instead of guessing at the reef.
Part of this page is live and part is not.
See the source list at the bottom for exactly which feed answered.
20:00 local · 2026-10-05
38% — the read for this hour
Swell
0.78 m
Period
9 s
Swell from
150°
Wind
1.3 m/s
Wind from
313°
Air
26°C
Marginal — one good hour at most. At Arugam Bay on this hour the read is 38%. What earns it: wind quality at 1.3 m/s straight offshore. What costs it: direction match at 58° off the 92° peel. Not scored, because no real data exists: Peel speed, Tide window.
No hour today clears the "worth the drive" bar at Arugam Bay.
Tide window for a beachbreak: 0.8–2.2 m of water over the take-off; below 0.30 m it works across the tide matters and the reef is exposed.
Dashed line is the tide above MLLW, solid line is the swell height. Column height is the engine score for that hour. Faded columns are gated. The hour you select is in the URL, so this page is shareable as-is.
Tide station
No tide station in range, so no tide value is shown anywhere in this app.
Signature interaction
Drag the tide and watch the reef change its mind
The cross-section is drawn from the break's own reef slope. Every change re-runs the shared engine on the server and returns a fresh seal — this control cannot work without the API.
The dashed arrow is the peel, at c = √(g·depth). More water over the take-off means a faster peel, which is why the same swell behaves differently at low and mid tide.
Re-solved by swellread-engine/2026.10.1
- Water over take-off
- exposed
- Break height
- —
- Peel speed
- —
- Wave power
- 3.5 kW/m
Marginal — one good hour at most. At Arugam Bay on this hour the read is 38%. What earns it: wind quality at 1.3 m/s straight offshore. What costs it: direction match at 58° off the 92° peel. Not scored, because no real data exists: Peel speed, Tide window.
Every factor, re-weighted for this tide
- Swell power3.5 kW/m · 5.7%
- Peel speedneeds a tide height
- Wind quality1.3 m/s straight offshore · 16.2%
- Tide windowno verified tide in range
- Direction match58° off the 92° peel · 3.5%
- Period cleanliness9.2 s · 12.6%
Show your working
Every factor, its weight, and the arithmetic behind it
Weights are renormalised over the factors that have real data behind them. A factor with no data is dropped and said so, never quietly scored at zero.
- Swell power3.5 kW/m · 5.7%
weight 0.355
- Peel speedneeds a tide height
weight 0.000 — dropped, not guessed
- Wind quality1.3 m/s straight offshore · 16.2%
weight 0.323
- Tide windowno verified tide in range
weight 0.000 — dropped, not guessed
- Direction match58° off the 92° peel · 3.5%
weight 0.194
- Period cleanliness9.2 s · 12.6%
weight 0.129
engine seal 002867d08c26ae41484af4fc38c14d8d91fbd36ee7fa9ae1f58f13d0d48e5b3d6369f203f7beb8da8d7ca2413c58809d
Swell power
P = 1/16 · rho · g · Hs² · Tp = 0.628 · 0.78² · 9 = 3.5 kW/m, against a 22 kW/m "serious day" reference.
Peel speednot scored
Peel speed is shallow-water celerity, so without a verified tide height there is no depth to take the square root of. This factor is dropped rather than guessed.
Wind quality
Wind is straight offshore at 1.3 m/s. Alignment = 1 − (1 + cos 163°)/2 = 0.98; speed envelope at 1.3 m/s = 0.51. Product 0.50.
Tide windownot scored
This break has no NOAA CO-OPS tide station in range, so the tide window cannot be scored. Weights are renormalised without it instead of substituting a guess.
Direction match
Swell from 150°, this break peels cleanly from 92°. 58° of error: inside 12° is full marks, past 75° the swell wraps the headland and does not arrive.
Period cleanliness
Tp = 9.2 s. Energy organises between 6 s and 9.5 s; beyond 14 s the swell stands up steeper than a shallow reef can hold, so the score is eased off by up to 35%.
Provenance
Every number above came from one of these
- liveOpen-Meteo Marine APICC BY 4.0, non-commercial attribution requiredfetched 2026-10-04 21:10 UTC168 hourly rows, swell and wind wave.
- liveOpen-Meteo Forecast APICC BY 4.0, non-commercial attribution requiredfetched 2026-10-04 21:10 UTC168 hourly rows, wind and air.
- fallbackNOAA CO-OPS tide predictionsU.S. Government public domainfetched 2026-10-04 21:10 UTCNo NOAA CO-OPS station is in range for this break, so no tide value is available and the tide factor is dropped.
Snapshot generated 2026-10-04T21:10:30.501Z. Break orientation, reef slope and take-off depth come from this project's catalogue and are labelled as estimates, not survey data.