The four alert levels
For U.S. and Canadian coasts, the National Weather Service describes four tsunami alert levels. A warning means a tsunami that may cause widespread flooding is expected or already occurring. Dangerous flooding and strong currents are possible and can continue for hours or days. Evacuation is recommended: move to high ground or inland, and follow local officials. An advisory means a tsunami with potential for strong currents or waves dangerous to people in or very near the water. Stay out of the water and away from beaches and harbors. A watch means a distant earthquake has occurred and a tsunami is possible. Stay tuned and be ready to act. An information statement means an earthquake occurred but there is no threat, or the source was very far away and the threat is not yet clear. In most of those cases there is no threat of a destructive tsunami.
Warnings, advisories, and watches can be updated or cancelled. An advisory, watch, or information statement can be upgraded if the threat is judged larger than first thought.
How alerts are sent
The Weather Service says tsunami warnings are broadcast on local radio and television, marine radio, wireless emergency alerts, NOAA Weather Radio, and NOAA sites including tsunami.gov. Outdoor sirens, local officials, text alerts, and phone calls may also be used. This website is not one of those channels.
Natural warnings
There may not be time for an official message. If you are on the coast and you feel a strong or long earthquake, see the ocean rise or fall suddenly, or hear a loud roar from the ocean, the Weather Service says a tsunami may follow and that this is your warning. Move to a safe place. Do not wait for an official instruction.
What the buoys on this site are
What a DART station is, and what the markers on the live map are not, is on the DART buoy page. A highlighted buoy is not a tsunami forecast and not a substitute for tsunami.gov.