West Coast/Alaska Tsunami Warning Center

Operations Manual

NOAA/NWS/WCATWC

910 South Felton Street

Palmer, Alaska 99645

http://wcatwc.arh.noaa.gov

Section 5.2: Message Definitions

Last Updated: 2/2004

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Tsunami Warning: Indicates that a tsunami is imminent and that coastal locations in the warned area should prepare for flooding. The initial warning is typically based on seismic information alone. Earthquakes within the WCATWC area of responsibility (AOR) over magnitude 7.0 trigger a warning covering the coastal regions within 2 hours tsunami travel time from the epicenter. When the magnitude is over 7.5, the warned area is increased to 3 hours tsunami travel time. For earthquakes outside the WCATWC AOR, warnings are only issued for earthquakes greater than magnitude 7.5 and for those locations within 3 hours tsunami travel time of the leading edge of the wave. As water level data showing the tsunami is recorded, the warning will either be cancelled, restricted, expanded incrementally, or expanded to cover the entire WCATWC AOR in the event of a major tsunami.
For an example CLICK HERE.

Tsunami Watch: An alert issued to areas outside the warned area. The area included in the watch is based on the magnitude of the earthquake. For AOR earthquakes over magnitude 7.0, the watch area is 1 hour tsunami travel time outside the warning zone. For all earthquakes over magnitude 7.5, the watch area is 3 hours tsunami travel time outside the warning zone. The watch will either be upgraded to a warning in subsequent bulletins or will be cancelled depending on the severity of the tsunami.
For an example CLICK HERE.

Tsunami Advisory: A message issued when the Pacific Tsunami Warning Center has issued a warning for an event outside the WC/ATWC AOR which poses no imminent threat to the AOR. The event is either far enough away so that no AOR region is within a watch/warning, OR the tsunami poses no threat to the AOR based on earthquake parameters, recorded tsunamis, historical tsunami information, and/or tsunami modeling. Advisories are updated hourly as PTWC issues bulletins, and can be upgraded to a watch or warning if necessary.
For an example CLICK HERE.

Tsunami Information Bulletin: Bulletins issued for earthquakes less than warning threshold, but greater than 6.5 which are not likely to trigger a tsunami. Unless further information is gathered on tsunami generation, only one Tsunami Information Bulletin is issued for an event.
For an example CLICK HERE.

Tsunami Information Message: Information messages issued when smaller earthquakes (greater than magnitude 4.0, but less than 6.5) may be felt near coastal areas. These messages are issued to assure coastal residents and emergency managers that there is no tsunami danger.
For an example CLICK HERE.