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A tsunami warning means dangerous coastal flooding and powerful currents are possible, so move to high ground or inland and follow local evacuation instructions. A tsunami advisory means dangerous waves or currents are possible near the water, but significant inundation is not expected; stay out of the water and away from beaches and waterways. A tsunami watch means the area may be affected later, while the danger level there is still undetermined; stay informed and be ready to act. These definitions are from the U.S. Tsunami Warning Centers’ domestic alert system for U.S. and Canadian coastlines and the British Virgin Islands. Other countries may use different labels or thresholds. For a live event, follow the current official message and local emergency-management instructions.
The three alerts at a glance
| Alert | What it means | What you should do |
|---|---|---|
| Warning | A tsunami capable of dangerous coastal flooding and powerful currents is imminent, expected, or occurring. Widespread inundation is possible. | Move to high ground or inland, leave the evacuation zone by the route local officials specify, and follow official instructions. |
| Advisory | Strong currents or waves dangerous to people in or very near the water are possible. Significant inundation is not expected in areas covered by the advisory. | Stay out of the water and away from beaches, shorelines, harbors, rivers, and other waterways until officials say conditions are safe. |
| Watch | The area may later be affected, but the danger level for that area has not yet been determined. | Stay informed, review how you would leave, and be prepared to act if the message is upgraded. |
The labels describe different hazards and public actions, not merely three confidence levels for one forecast. The official definitions are maintained by the U.S. Tsunami Warning Centers.
What a tsunami warning means
The hazard
A warning is the highest-action domestic tsunami alert. It means dangerous coastal flooding and powerful currents are possible, with a tsunami that may produce widespread inundation imminent, expected, or already occurring. The wording does not require you to wait for water to arrive or for a second confirmation. Conditions at different beaches, bays, rivers, and elevations can vary, so the message may cover a broad area even though the most severe effects are concentrated in particular locations.
Your immediate response
- Leave the shoreline and other low-lying coastal areas immediately when the warning or a local evacuation order applies to your location.
- Go to high ground or travel inland using the evacuation route designated by local emergency management. Do not choose a route that takes you toward a beach, harbor, river mouth, or other waterway.
- Follow instructions from local emergency officials, law enforcement, and emergency messages. If officials direct a wider evacuation than the warning map appears to show, follow the local direction.
- Continue monitoring official updates while moving, but do not delay departure to collect more information when the warning applies to you.
A warning is not an assurance that every point inside a highlighted forecast zone will be flooded. It is a direction to take protective action because dangerous effects are possible within the warned area.
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Why waiting for visual evidence is unsafe
Tsunamis can arrive as a series of waves, and the first wave is not necessarily the largest. Dangerous currents can persist after the shoreline looks calmer. Because a warning can be issued while a tsunami is still traveling, waiting to see water rise, waiting for a siren, or returning after one wave can expose you to later surges and currents. Remain in the safe location until local officials give the all-clear.
What a tsunami advisory means
The hazard
An advisory signals a real water hazard without the significant inundation expected under a warning. Waves or currents can still injure or kill people in the water, on beaches, near rocks, in marinas, or along waterways connected to the sea. Boats can be damaged at docks or in channels, and people who enter the water to watch conditions can be swept away.
The correct action
- Stay out of the ocean, bays, rivers, ports, and other waterways in the advisory area.
- Keep away from beaches, shorelines, jetties, rocks, and harbor entrances where currents may accelerate.
- Do not treat a lack of visible flooding as permission to swim, surf, paddle, fish, or sightsee.
- Check local instructions for closures, harbor restrictions, and the time officials expect conditions to improve.
An advisory normally does not call for the broad inland evacuation associated with a warning, but local authorities can issue additional restrictions for particular sites. The local order controls where it is more specific than the regional advisory.
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The hazard
A watch is an early notice that a tsunami may later affect the area. The danger level at that location is not yet known. Seismic analysis, water-level observations, and forecast information may still be developing, so a watch is not a statement that destructive impact is certain and is not a reason to assume that no impact will occur.
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How to use the time
- Keep receiving official messages and note the time of the next scheduled update if one is provided.
- Check the evacuation map for your address, workplace, school, or lodging and identify high ground or an inland destination.
- Charge phones, gather essential medicines and documents, and account for children, older adults, people with disabilities, and pets.
- Be ready to leave if the watch becomes a warning or advisory, or if local officials issue an evacuation instruction.
Do not evacuate solely because the word watch appears if officials have not directed an evacuation for your area; instead, use the preparation time and follow the message’s specific instructions. A watch can be upgraded, downgraded, or canceled as evidence improves.
How alerts change during an event
A watch is not a guaranteed step before a warning
Warning centers often issue a watch early for places that could eventually be affected, before a destructive tsunami is confirmed. As more information arrives, that watch may become a warning, become an advisory, or be canceled. It is therefore wrong to describe the three labels as a fixed sequence or to assume that every watch will become a warning.
Information statements
An information statement reports an earthquake or tsunami of interest. In most cases it indicates that no destructive basin-wide tsunami threat is expected and helps prevent unnecessary evacuations. It is not a permanent guarantee: later observations can lead to a watch, advisory, or warning. Read the complete statement rather than relying on a headline or social-media summary.
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Updates, geographic changes, and cancellation
Warnings and advisories can be adjusted geographically, updated, upgraded, downgraded, or canceled. A cancellation means the warning center’s evaluation no longer supports that alert for the covered area. The final decision that a particular place is safe belongs to local and state emergency-management officials, who can keep restrictions in place because of local currents, flooding, damage, or continuing hazards. Do not return simply because an alert disappeared from one app; wait for the local direction that applies to you.
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Natural warning signs can come first
The U.S. Tsunami Warning Centers identify two broad ways to receive a warning: an official message and a natural warning. You may receive one without the other. In a tsunami hazard zone, natural signs require immediate action even if your phone is silent and no siren is sounding.
- Strong or long earthquake shaking: If the ground shakes so strongly or for so long that it is difficult to stand, protect yourself during the shaking and then move away from the coast as soon as it stops.
- A loud roar from the ocean: An unusual roaring or rumbling sound can precede a local tsunami.
- Unusual ocean behavior: The water may suddenly recede, expose the seafloor, or rise rapidly. Either a dramatic withdrawal or a fast rise is a warning sign.
Do not go toward the shore to investigate an unusual waterline. Move to high ground or inland and stay there until local officials provide an all-clear. A local tsunami can arrive before an official alert is disseminated, leaving little time for a second source of confirmation.
How official alerts reach you
In the United States, tsunami information may be delivered through several channels. The official FAQ lists local radio and television, marine radio, wireless emergency alerts, NOAA Weather Radio, NOAA websites such as Tsunami.gov, social media, outdoor sirens, and local notification systems. No single channel is guaranteed to reach every person, particularly during a power outage or when traveling.
Build a layered way to receive messages
- Enable wireless emergency alerts on your phone and keep location services configured as your device manufacturer recommends.
- Subscribe to your city, county, tribal, or state emergency-notification service; these systems can provide route-specific evacuation instructions.
- Know where local sirens and public-address systems are located, but do not assume that a siren can be heard indoors, at a distance, or during an earthquake.
- Keep a battery-powered or hand-crank NOAA Weather Radio if it fits your preparedness plan. It is one supporting channel, not a substitute for natural-warning awareness or local instructions.
- When boating, monitor marine radio and harbor authorities as well as land-based alerts.
During an event, keep monitoring official information because the alert area, expected arrival information, and protective action can change.
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Who issues the message and where the definitions apply
The alert definitions above describe the domestic system used for U.S. and Canadian coastlines and the British Virgin Islands. The National Tsunami Warning Center serves the continental United States, Alaska, and Canada. The Pacific Tsunami Warning Center directly serves Hawaii, U.S. Pacific and Caribbean territories, and the British Virgin Islands.
For international Pacific and Caribbean events, the centers provide guidance to national authorities. Each country decides which alert to issue for its own coastlines, so a foreign authority may use different names, colors, thresholds, or public instructions. U.S. territories should use messages specifically issued for their regions rather than applying a mainland message to every island or coastline.
If you are outside the United States or Canada, rely on your national meteorological or civil-protection authority for the local definition. The practical principle remains the same: follow the current official message for your exact location and obey local emergency officials.
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A highlighted forecast zone is not automatically an evacuation zone or an expected inundation boundary. On U.S. maps, the highlighted zone can extend inland beyond the area forecasters expect to be inundated. The shading communicates where the message applies for forecasting and public awareness; it does not mean that every colored address will be underwater.
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- Read the written alert for the named coast, forecast zone, and action. Do not rely on color alone.
- Compare the message with your community’s evacuation map, which uses local elevation, roads, bridges, and safe areas.
- If the map and a local order appear to conflict, ask local emergency management or law enforcement, or the relevant National Weather Service Weather Forecast Office.
- Remember that a warning can cover an area where only some shorelines experience the most severe flooding, while currents may remain dangerous in places that do not flood.
The map’s purpose is to show the alert’s geographic coverage, not to predict the exact waterline at every property.
What to do in common situations
You receive a warning at home or work
Take the evacuation route you have already identified and move to high ground or inland. Leave immediately rather than waiting for a second notification. If roads are blocked, follow local directions to the nearest safe location; do not drive toward the coast to collect people or belongings. Once safe, keep monitoring official updates and remain there until local authorities give the all-clear.
You receive an advisory while at the beach or harbor
Exit the water and move away from the shoreline, harbor entrance, and connected waterways. Follow beach-closure or harbor instructions. An advisory is not an invitation to watch waves from a jetty or to launch a boat for a closer look; currents can be hazardous even without obvious flooding.
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Confirm whether the watch includes your current location and identify the nearest evacuation route and high ground before conditions change. Keep your phone charged, tell companions what would trigger departure, and monitor the next official update. Do not assume that an alert for one coast applies to every coast in the region.
You feel a strong earthquake or see unusual water behavior
Treat the natural sign as your warning in a hazard zone. Protect yourself during the earthquake, then move inland or uphill without waiting for a siren, app notification, or official bulletin. Warn people nearby as you leave if doing so does not delay your own evacuation, and stay away from the shore until officials say it is safe.
Mistakes that lead to dangerous decisions
- Confusing a watch with an evacuation order: A watch means possible later impact and an undetermined local danger; read the action line and local instructions.
- Treating an advisory as harmless: Significant inundation may not be expected, but currents and waves can still be deadly near water.
- Waiting for an official message after natural signs: Local tsunamis can arrive before alerts reach phones, television, or sirens.
- Assuming cancellation equals immediate safety: Local officials make the final decision for a specific area and may maintain restrictions.
- Interpreting every colored map area as flooded: Forecast zones, inundation zones, and evacuation boundaries serve different purposes.
- Following an old screenshot or forwarded message: Alerts are updated and can change in both level and geography; use the current official source.
- Returning after the first wave: A tsunami is a series of waves and later waves or currents can be more dangerous.
A simple decision rule
Use the alert label and the action together:
- Warning: leave the threatened coast for high ground or inland and follow evacuation instructions.
- Advisory: leave the water and stay away from beaches and waterways.
- Watch: monitor official information, prepare your route and supplies, and be ready to act.
- Natural warning sign: act immediately in a hazard zone, even without an official alert.
For any specific event, the current message and local emergency-management direction take precedence over a general explanation of the labels. Check the official message definitions, the current alert issued for your area, and local evacuation instructions.
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