West Coast/Alaska Tsunami Warning
Center
Operations Manual
NOAA/NWS/WCATWC
Palmer,
Section 5.2:
Message Definitions
Last
Updated: 1/2008
West
Coast/Alaska Tsunami Warning Center (WCATWC) product definitions will change to
the definitions provided below on February 12, 2008. The products issued by the center are
warning, watch, advisory, and information statement. Each has a distinct meaning relating to local
emergency response. In summary:
Warning -> Inundating wave possible -> Full
evacuation suggested
Watch -> Danger level not yet known -> Stay
alert for more info
Advisory -> Strong currents likely -> Stay away from the shore
Information -> Minor waves at most -> No
action suggested
Based
on seismic data analysis or forecasted amplitude (dependent on whether the
center has obtained sea level data), WCATWC will issue the appropriate
product. Procedural criteria are
summarized in the linked bar chart. Warnings and Advisories suggest that action
be taken. Watches are issued to provide
an early alert for areas that are distant from the wave front, but may have
danger. Once the danger level is
determined, the watch is upgraded to a warning or advisory, or canceled. The full definition of each message is given
below. See Section
5.1 for examples and descriptions of all WCATWC products.
Tsunami Warning - a tsunami warning is issued
when a potential tsunami with significant widespread inundation is imminent or
expected. Warnings alert the public that widespread, dangerous coastal
flooding accompanied by powerful currents is possible and may continue for
several hours after arrival of the initial wave. Warnings also 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. To provide the earliest possible
alert, initial warnings are normally based only on seismic information.
For an example of
the National Weather Service (NWS) format tsunami warning CLICK HERE. For a warning cancellation, CLICK HERE.
Tsunami Watch - a tsunami watch is issued to
alert emergency management officials and the public of an event which may later
impact the watch area. The watch area may be upgraded to a warning or
advisory - or canceled - based on updated information and
analysis. Therefore, emergency management officials and the public should
prepare to take action. Watches are normally issued based on seismic
information without confirmation that a destructive tsunami is underway.
For an example of
the NWS format tsunami watch CLICK HERE.
Tsunami Advisory - a tsunami advisory is issued due
to the threat of a potential tsunami which may produce strong currents or waves
dangerous to those in or near the water. Coastal regions historically
prone to damage due to strong currents induced by tsunamis are at the greatest
risk. The threat may continue for several hours after the arrival of the
initial wave, but significant widespread 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 are
normally updated to continue the advisory, expand/contract affected areas,
upgrade to a warning, or cancel the advisory.
For an example of the NWS format tsunami
advisory CLICK HERE.
Tsunami Information Statement - a tsunami information statement is issued to inform emergency management
officials and the public that an earthquake has occurred, or that a tsunami
warning, watch or advisory has been issued for another section of the
ocean. In most cases, information statements are issued to indicate there
is no threat of a destructive tsunami and 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
destructive local tsunamis. Information statements may be re-issued with
additional information, though normally these messages are not updated.
However, a watch, advisory or warning may be issued for the area, if necessary,
after analysis and/or updated information becomes available.
For an example of
the NWS format information statement CLICK HERE.