Sado (Ryotsu) · Japan

8.5

wave 0.2 m

visibility7m

Dive today — wave, wind and visibility.

Sources: Open-Meteo · Copernicus — high confidence · data 00:08

Sources & confidence

Sources: Open-Meteo · Copernicus
Method: spearo sea-state engine: consensus of up to 6 models + satellite clarity (ZSD) + buoy-bias checks
Freshness: Re-read every hour, per coast

Compiled by the spearo sea-state engine · How it works →

The verdict comes from seven water factors and hard safety gates — not ten tabs. Go or stay.

How we score the water

Our own model

Our own forecast engine — not a third-party widget. It weighs these water factors into one go-or-stay verdict for this coast; the 0–10 dial is that verdict, read out as a number.

Swell & wave memory: Height, period and direction of the swell, plus the wake of recent storms — an old storm still stirs the water, and the engine remembers.
Wind & gusts: Speed and gusts, hour by hour — wind speed and an onshore push chop the surface and cut visibility.
Tide phase: Timing and range of the tide, calibrated per coast — big spring tides pull the verdict toward caution.
Water temperature: Sea-surface temperature — sharply cold water vetoes a green verdict.
Currents & outflow: Direction and drift of the current — it pushes you, and it drags turbid coastal water across where you dive.
Rain runoff & air clarity: Rain muddies the water inshore through land runoff, while fog and haze cut visibility at the surface.
Coast shape & exposure: How the coast faces the swell — a sheltered cove keeps the water clean; an exposed, head-on point takes a penalty.

Safety gates

Thunderstorm forecast — an instant red, no exceptions.
An official warning (MeteoAlarm / IPMA) — yellow, or red for the higher ranks.
Missing input data — a would-be green is capped to yellow rather than overstated.
Strong disagreement between forecast models — a green day is pulled back to yellow.
Night hours — where night spearfishing is banned by law the window is forced red; where it is legal (Australia outside NSW, New Zealand, South Africa) it is capped at yellow, never green.

It all folds into a single 0–10 score and one verdict: go or stay.

A forecast, not a guarantee — the sea has the last word.

Where to get in, where to hunt

Entry points with coordinates

Seabed relief — promising ground

This verdict — in your pocket. Open the app for the week's window.

More spots

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Shikoku, Kii & Ise-Shima

Hokkaido

Hakodate

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Where to get in
off the rocks.

Scouted entries, coloured by today. The colour is the sea state at the spot, not a guarantee: the wash and a slippery entry you judge on site.

Open the seafloor map

FutatsugameSado (Ryotsu)

borderline

Speargun prohibited, hand spear (yasu) allowed under Niigata Fisheries Adjustment Rules, JFA list. Hand-held only, no trigger or launch device. No scuba; co-op shellfish and lobster are off-limits.

exposed head-on to the swell today

window: —

Swimming beach next to the twin Futatsugame islets, reached by a short walk down from the car park; very clear water for snorkelling over a sand-and-gravel bottom. Hand spear only — no speargun, no scuba.

Google Maps

Mushizaki beachSado (Ryotsu)

borderline

Speargun prohibited, hand spear (yasu) allowed under Niigata Fisheries Adjustment Rules, JFA list. Hand-held only, no trigger or launch device. No scuba; co-op shellfish and lobster are off-limits.

exposed head-on to the swell today

What's in season,
what the law says.

In season now

no targets this month

Law

Japan: spearguns and scuba/hookah are banned for all recreational fishers nationwide (Fisheries Agency prefectural gear table); a hand spear (yasu) is allowed only in some prefectures (e.g. Okinawa, Kagoshima, Nagasaki, Kochi, Mie); abalone, lobster, octopus and sea urchin in fishery-right areas belong to the local co-op, and marine park zones are closed. Check current rules locally.

Safety protocol

Sets: watch the wave trains ≥15 min before entering; Hmax ≈ 2×Hs, the wash can run 50 m past the foam line. A lull >10 min with period >12 s = a big set «overdue», do NOT enter; enter right after a full set passes and re-check at minute 30.
Exit FIRST: find your exit AND a backup before entering. On a rocky/boulder shore a 0.5 m rise in swell can make the exit impossible — getting pinned/unable to climb out is the main killer.
Headland rip: prominent points often have a permanent topographic rip regardless of the model — locate it, enter/exit on the windward side, never swim against it.
Cold: wetsuit per the SST chip; the first shiver = a metabolic surge and a drop in breath-hold → get out at the first steady shiver. Cap the session at 45–60 min below 15 °C.
Solo discipline: buoy up; tell someone the spot and exit time; conservative breath-hold (never push it in cold/murky/surfy water); visibility <3 m — don't enter.
Afternoon wind: on many coasts the wind builds from midday — plan to be out of the water by midday; the chop builds — get out.
UV 11:00–15:00 (UVI ≥6): sunscreen and cover up on the surface interval.
Solo is a fundamental risk (hypoxic blackout with no buddy). Any doubt = No-go.