HKO and CWA Marine Warnings: What Each Signal Means and Where to Check It
Every tide table on this site — and every official one — answers one question: where will the astronomical water be? None of them answers the question that actually decides your day: what is the weather doing to that water? Wind piles it against a coast, distant storms send long swell under a blue sky, and a tropical cyclone can lift the entire sea surface a metre or more above the predicted tide. Both the Hong Kong Observatory (HKO) and Taiwan's Central Weather Administration (CWA) run warning systems for exactly this. Here is what each signal means and where the live versions live.
Key takeaways
- Tide tables are astronomical; wind, pressure and surge are not — warnings are the correction layer, not an optional extra.
- Hong Kong: numbered tropical cyclone signals (No. 1 standby through No. 10 hurricane) plus the separate Strong Monsoon Signal (winds over 40 km/h, gusts over 70 km/h).
- Taiwan: marine strong wind advisory for sea areas at Beaufort 6+, township strong-wind light alerts (yellow/orange/red), long-swell messages, and typhoon sea/land warnings.
- Any signal in force = treat exposed flats, piers and platforms as closed, whatever the tide table promised.
- Check at the source: HKO warnings · CWA warnings.
Hong Kong: the numbered cyclone signals
HKO's tropical cyclone warning system escalates through numbers everyone in the city knows. The meanings relevant to shore users:
| Signal | Trigger (HKO criteria) | What it means on the shore |
|---|---|---|
| No. 1 Standby | A tropical cyclone is centred within about 800 km of Hong Kong and may affect it. | Plan for deterioration; seas already run above the table on exposed coasts. |
| No. 3 Strong Wind | Strong wind blowing or expected generally, with gusts rising. | Exposed piers and flats are effectively off-limits; surge begins to distort tide levels. |
| No. 8 Gale/Storm (by quadrant) | Gale or storm force wind expected, signal naming the incoming direction. | Stay away from the entire coastline; storm surge can raise water far above prediction. |
| No. 9 / No. 10 | Increasing gale/storm; hurricane-force winds imminent or occurring. | Emergency conditions; the tide table is irrelevant. |
Alongside the numbers sits the Strong Monsoon Signal — the "black ball". It is issued when monsoon winds are blowing in excess of, or are expected to exceed, 40 km/h, with gusts that may exceed 70 km/h, anywhere in Hong Kong. It is not part of the cyclone numbering precisely because the danger is "only" wind — but for anglers and photographers, a strong monsoon alone is enough to make breakwaters lethal and to push actual water levels well off the predicted curve.
Taiwan: advisories tuned to the sea
CWA's system speaks in advisories and light alerts. The ones that matter for tide-dependent plans:
- Marine strong wind advisory (海上強風特報). Issued for named sea areas when average wind is expected to reach Beaufort 6 or above — the small-craft and shore-angler threshold. Fishery weather pages and the Fisheries Radio broadcast carry it.
- Land/township strong wind light alerts. A three-colour scheme — yellow for mean wind Beaufort 6 or gusts 8, orange for mean 9/gusts 11, red for mean 12/gusts 14 — now issued down to township level, so coastal districts get specific warning even when inland cities do not.
- Long-swell real-time messages (長浪即時訊息). Distant weather sends long-period swell that arrives under clear skies; these messages flag sea areas and harbours where buoy-observed swell is running dangerous. Long swell is the classic mechanism behind rogue-wave incidents on Taiwan's north and northeast rocky coasts — including the Keelung and northeast-cape marks near our Keelung tide table.
- Typhoon warnings (颱風警報). Sea (海上) and land (陸上) typhoon warnings delineate the threat areas; a sea warning alone still means storm surge and swell for the coast.
How warnings interact with a tide table
The classic dangerous combination is a storm surge riding a high tide: if a cyclone pushes an extra metre of water onto a coast whose table already predicts a 2.5 m high, the effective level is 3.5 m — flooding ground the astronomical table calls safe. The reverse also happens: strong offshore winds can hold water below a predicted low, stranding boats and exposing flats further than expected. Neither effect appears in any tide table, which is exactly why both HKO and CWA attach "actual conditions may differ" caveats to their predictions. The operational habit is: read the tide table for the plan, read the warnings for permission to execute it. That habit, applied to flats and estuaries specifically, is the core of our beach-safety guide.
Where to check, and how often
- The night before: warnings page for your side of the strait — HKO current warnings or CWA sea-area warnings.
- At first light: check again — advisories upgrade fast in monsoon season.
- On site: the flag or notice at lifeguarded beaches, harbour-office notices at fishing harbours, and the sky itself. Signals are guidance; the sea in front of you is data.
For anglers, CWA's fishery weather forecast and the Fisheries Radio broadcasts exist precisely for this audience; for everyone else the websites and official apps carry the same signals with maps. Our tide tables stay useful through all of it — but they earn their keep only when the warnings column is clear.
Signals change — this page is orientation, not a live feed
Definitions and thresholds summarized here follow the official HKO and CWA publications as of November 2026 and are described for education; the authorities can and do refine their systems. Before any trip, confirm current signals at the official pages linked above. Nothing on this site is a substitute for an official warning.