How navigational warnings reach ships: NAVAREAs, NAVTEX and satellites
Written by seahazards · updated 2026-09-24 · numbers recounted nightly
A buoy goes missing off Brazil at dawn; by noon every ship bound for that coast has the warning. That happens through a layered system agreed between governments, and knowing the layers explains why the same danger can appear in several messages.
Twenty-one areas, twenty-one coordinators
The World-Wide Navigational Warning Service, set up by the International Maritime Organization and the International Hydrographic Organization, divides the oceans into NAVAREAs. Each has a coordinating country responsible for collecting information about dangers in its waters — from its own hydrographic office, navy, coast guard, port authorities and neighbouring countries — and broadcasting it as numbered NAVAREA warnings.
Five Arctic areas were added in 2011, bringing the total to 21. The United States coordinates two of them, NAVAREA IV and XII, and also relays warnings from other areas as HYDROLANT, HYDROPAC and HYDROARC messages — which is why so much of the world's warning history can be read in the U.S. archive.
| NAVAREA IV · United States | 19,367 |
| NAVAREA V · Brazil | 16,309 |
| NAVAREA XII · United States | 11,921 |
| NAVAREA VIII · India | 11,397 |
| NAVAREA XI · Japan | 10,349 |
| NAVAREA III · Spain | 10,120 |
| NAVAREA VI · Argentina | 5,571 |
| NAVAREA II · France | 5,541 |
| NAVAREA IX · Pakistan | 2,965 |
| NAVAREA XV · Chile | 2,900 |
Attributed by the message's own series or the NAVAREA an NGA relay names; each area's full traffic is larger.
Coastal warnings and NAVTEX
Below the long-range layer, countries broadcast coastal warnings for their own waters, and local warnings for harbours and approaches. Many coastal warnings go out on NAVTEX, an automated medium-frequency service that prints text on a small receiver on the bridge; stations reach a few hundred miles offshore, and each message carries a station letter, a subject letter and a number, so a receiver can choose which subjects to print and skip messages it has already printed.
A danger close to shore may therefore appear as a coastal warning, a NAVAREA warning, and later an NGA relay of that NAVAREA warning. On this site each is a separate record, and the related-warnings pages group messages that describe the same place and time.
1,685 messages use it, 3 of them in force now; most often in North Atlantic Ocean, North Pacific Ocean, South Pacific Ocean.
Satellite broadcasts and the safety system around them
Beyond radio range, NAVAREA warnings reach ships by satellite: Inmarsat's SafetyNET service, and more recently Iridium's, broadcast them to every ship inside the area. Together with digital selective calling, distress beacons and NAVTEX, these services form the Global Maritime Distress and Safety System, mandatory for ships under the SOLAS Convention since 1999.
Warnings stay in force until cancelled, and coordinators regularly broadcast the list of warnings currently in force so that a ship entering an area can check it holds them all. seahazards reads several of those in-force lists directly; the coverage page says which, and since when.
35 messages use it, 1 of them in force now.