Notice to Mariners (NtM)

A periodic bulletin issued by a national hydrographic office to keep nautical charts and publications up to date, carrying corrections to charts, light and buoy changes, wreck and obstruction reports, and navigational and security warnings. The UK Hydrographic Office publishes the weekly Admiralty Notices to Mariners; the US NGA issues its own. Urgent items also go out as Navigational and Coastal Warnings under the IMO/IHO Worldwide Navigational Warning Service, including reported piracy, exercise areas, and restricted zones.