Barrier 2 — Lamb Holm to Glimps Holm — is the most exposed of the four causeways. Scapa Flow itself is too small a body of water to build a real sea, so a westerly wind is almost never a problem here. The danger comes from the East through Southeast, off the open North Sea via Holm Sound — that, stacked on a high spring tide, is what puts water over the road.
Built in 1944 from rubble, concrete blocks and sunken WWII block ships, the barriers sit permanently above normal high water — this isn't a ford that floods at high tide. But the road surface on Barrier 2 is low enough that when the sea is already running high, a gust off the North Sea can throw a wave clean over the top.
The predictor combines three things: tide height, wind, and actual wave height. Tide is predictable weeks ahead. Wind and waves are only forecast reliably a few days out, and wind direction matters as much as its speed — a gale from the west has little fetch to work with on Scapa Flow, but the same gust from the East or Southeast comes straight off the North Sea and hits the causeway broadside. Wave height comes from a separate sea-state model, so it already reflects the real, fetch-limited geometry of Holm Sound rather than a guess from wind alone. Risk compounds: any one factor running high is worth watching; two or more together is when it gets dangerous.
Tide, wind and sea state, aligned together — the window where all three forecasts overlap.
| When | Tide | Wind | Gust | From | Wave | Swell | Risk |
|---|
Tide-only — no wind or wave forecast reaches this far out yet. Risk shown is tide height alone.
Tide predictions are primarily for St Mary's (Scapa Flow), an official UK Admiralty station roughly 1km from Barrier 2, via UKHO EasyTide. That free feed only reaches about a week ahead, so days beyond it fall back to Kirkwall (~13km away, scraped daily from tide-forecast.com) — each row in the log below is labelled with whichever station it actually came from. Heights are relative to chart datum (approx. Mean Lower Low Water). Wind is the ICON-EU model and waves are its companion ICON-EU Wave model, both via Windy.com's point-forecast API, centred on Barrier 2, refreshed every 30 minutes.
This is a tide, wind and wave estimate, not an official closure notice. Before crossing, check Orkney Islands Council's road conditions page, Traffic Scotland, and the Met Office coastal warnings for Orkney.