West Coast/Alaska Tsunami Warning
Center
Operations Manual
NOAA/NWS/WCATWC
Palmer,
http://wcatwc.arh.noaa.gov
Section 5.2:
Message Definitions
Last Updated: 7/2006
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Tsunami
Warning: The highest level of tsunami alert.� Warnings are issued by the TWCs due to
the imminent threat of a tsunami from a large undersea earthquake, or following
confirmation that a potentially destructive tsunami is underway.� They may initially be based only on seismic information as a means of providing
the earliest possible alert. Warnings advise that appropriate actions be taken
in response to the tsunami threat.� Such
actions could include the evacuation of low-lying coastal areas and the
movement of boats and ships out of harbors to deep waters.� Warnings are updated at least hourly or as
conditions warrant to continue, expand, restrict, or end the Warning.
For an example
of the National Weather Service (NWS) format tsunami warning CLICK HERE.
Tsunami Watch: The second highest level of tsunami
alert.� Watches are issued by the TWCs based on seismic
information without confirmation that a destructive tsunami is underway.� It is issued as a means of providing advance
alert to areas that could be impacted by a destructive tsunami.� Watches are updated at least hourly to continue
them, expand their coverage, upgrade them to a Warning, or end the alert.� A watch for a particular area may be included
in the text of the message that disseminates a Warning for another area.
For an example
of the NWS format tsunami watch CLICK HERE.
Tsunami Advisory: The third highest level of tsunami alert.� Advisories are issued by the TWCs to
coastal populations within areas not currently in either warning or watch
status when a tsunami warning has been issued for another region of the same
ocean.� An Advisory indicates that an area is either outside the current warning
and watch regions, or that the tsunami poses no danger to that area. The Center
issuing the Advisory will continue to monitor the event, issuing updates at
least hourly. As conditions warrant, the Advisory will either be continued,
upgraded to a watch or warning, or ended.
For an example
of the NWS format tsunami advisory CLICK HERE.
Information
Statement: A text product issued to inform that an earthquake
has occurred and to advise regarding its potential to generate a tsunami.� In most cases, an Information Statement
indicates there is no threat of a destructive tsunami affecting the issuing
TWC�s AOR, and are used to prevent unnecessary evacuations as the earthquake
may have been felt in coastal areas.� An Information
Statement may, in appropriate situations, caution about the possibility of a
destructive local tsunami.� A
supplemental Information Statement may be issued if important additional
information is received such as a sea level reading showing a tsunami
signal.� An Information Statement may
also be upgraded to a watch or warning if appropriate.� Further, the Information Statement may be
used to recommend a warning when protocols agreed to by emergency management
authorities within an AOR so specify.
For an example
of the NWS format information statement CLICK HERE.
See Section
5.1 for examples and descriptions of all WC/ATWC products.