Definitions

The U.S. Tsunami Warning Centers issue tsunami messages to notify emergency managers, the public, and other partners about the potential for a tsunami following a possible tsunami-generating event. To provide messages as early as possible, the warning centers use preset criteria based on preliminary earthquake information, before a tsunami is detected, to help them decide when and for where to issue tsunami messages and what alert(s) to include. Subsequent messages and alerts are based on impact estimation resulting from additional seismic analysis, water-level measurements, tsunami forecast model results, and historical tsunami information.

Examples of tsunami messages

Domestic Tsunami Messages *

Domestic tsunami messages are issued for U.S. and Canadian coastlines and the British Virgin Islands. These messages include alerts and also serve to cancel alerts, when appropriate. There are four levels of tsunami alerts: warning, advisory, watch, and information statement. Each has a distinct meaning relating to local emergency response. Recommended protective actions vary within areas under warnings and advisories. Be alert to and follow instructions from local emergency officials because they may have more detailed or specific information.

Tsunami Warning – A tsunami warning is issued when a tsunami with the potential to generate widespread inundation is imminent, expected, or occurring. Warnings alert the public that dangerous coastal flooding accompanied by powerful currents is possible and may continue for several hours after initial arrival. Warnings alert emergency management officials to take action for the entire tsunami hazard zone. Appropriate actions to be taken by local officials may include the evacuation of low-lying coastal areas, and the repositioning of ships to deep waters when there is time to safely do so. Warnings may be updated, adjusted geographically, downgraded, or canceled based on updated information and analysis.

Tsunami Advisory – A tsunami advisory is issued when a tsunami with the potential to generate strong currents or waves dangerous to those in or very near the water is imminent, expected, or occurring. The threat may continue for several hours after initial arrival, but significant inundation is not expected for areas under an advisory. Appropriate actions to be taken by local officials may include closing beaches, evacuating harbors and marinas, and the repositioning of ships to deep waters when there is time to safely do so. Advisories may be updated, adjusted geographically, upgraded to a warning, or cancelled based on updated information and analysis.

Tsunami Watch – A tsunami watch is issued when a tsunami may later impact the watch area. The watch may be upgraded to a warning or advisory or canceled based on updated information and analysis. Emergency management officials and the public should prepare to take action.

Tsunami Information Statement – A tsunami information statement is issued when an earthquake or tsunami has occurred of interest to the message recipients. In most cases, information statements are issued to indicate there is no threat of a destructive basin-wide tsunami and to prevent unnecessary evacuations. Information statements for distant events requiring evaluation may be upgraded to a warning, advisory, or watch based on updated information and analysis.

A cancellation is issued after an evaluation of water-level data confirms that a destructive tsunami will not impact an area under a warning, advisory, or watch or that a tsunami has diminished to a level where additional damage is not expected.

International Tsunami Messages *

International tsunami messages are issued by the Pacific Tsunami Warning Center (PTWC) to international partners in the Pacific and Caribbean and Adjacent Regions for guidance only in support of the UNESCO/IOC Pacific Tsunami Warning and Mitigation System (PTWS) and the Tsunami and Other Coastal Hazards Warning System for the Caribbean and Adjacent Regions (CARIBE EWS). There are two types of international tsunami messages: tsunami threat messages and tsunami information statements. These messages do not include alerts. The primary purpose of these messages is to advise national authorities of the PTWC evaluation of the tsunami threat so they can determine, based on all information available to them, which alerts to issue for their coastlines, if any.

Tsunami Threat Message – A tsunami threat message is issued to officially designated national authorities of the PTWS or CARIBE EWS when a potential or confirmed tsunami is forecast to affect some or all coasts within those systems. Estimated arrival times for the first wave are provided for select locations. When sufficient data have been received to forecast tsunami waves, the message is updated to include this information. Messages also emphasize that a tsunami can adversely impact people, structures, and ecosystems on land or in nearshore marine environments. National authorities will determine the appropriate level of alert for each country and may issue additional or more refined information and instructions. Threat messages may be updated based on new information, data and analysis.

A final tsunami threat message is issued when the Pacific Tsunami Warning Center determines there is no further threat or that tsunami waves are now below threat levels in most places and are diminishing.

Tsunami Information Statement – A tsunami information statement is issued to national authorities when an earthquake or tsunami has occurred of interest to the message recipients. In most cases, information statements are issued to indicate there is no threat of a tsunami and to prevent unnecessary evacuations. Information statements may be upgraded to tsunami threats based on updated information and analysis.


* U.S. states and territories in the Pacific and Caribbean (American Samoa, Guam, Hawaii, Northern Mariana Islands, Puerto Rico, U.S. Virgin Islands) should refer ONLY to the Pacific Tsunami Warning Center messages specifically for their regions. International tsunami threat messages from the Pacific Tsunami Warning Center may mention U.S. states and territories, but they do not reflect the additional modeling and analysis conducted to fine tune forecasts and set alert levels for the United States and should not to be relied on by U.S. states and territories.