WCATWC: West Coast and Alaska tsunami warning center

NOAA and the National Tsunami Hazard Mitigation Program are conducting the first multi-state tsunami exercise for the U.S./Canadian Atlantic, Gulf of Mexico, Puerto Rico, and Virgin Islands coasts on April 2, 2009.

The exercise is intended to provide a framework for emergency management agencies to test and review tsunami response plans. The Participant Handbook can be downloaded by clicking on LANTEX09HandbookV3.pdf

Related note: WCATWC Product Change Effective February 12, 2008

WCATWC product definitions have changed to better align with other National Weather Service products and to provide more specific information regarding tsunami threat. The main change is to the Tsunami Advisory. Previously, a Tsunami Advisory indicated that a Tsunami Warning or Watch had been issued for another section of the ocean coast. As of February 12 2008, WCATWC Tsunami Advisories will be considered a low-level tsunami threat and indicate that a moderate tsunami impact is possible. No significant inundation is expected for areas under advisory, but strong currents dangerous to those in or very near the ocean are possible.

Further information: on WCATWC products is provided at wcatwc.arh.noaa.gov/Products/msgdefs.htm. The NWS Service Change Notice explaining the change can be viewed at www.nws.noaa.gov/om/notification/scn07-51ccatsunami.txt.

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.