How to Read NOAA Tsunami Warnings, Watches and Bulletins
During last week's earthquake off the coast of Japan, some U.S. media outlets inaccurately reported that the quake promoted a tsunami alert for the northwestern coast of the United States. The following information is intended to help news organizations communicate accurate, timely tsunami threats to the public.
(Logo: http://www.newscom.com/cgi-bin/prnh/20041022/DCF003LOGO )
Realm of Responsibilities:
NOAA's National Weather Service operates two tsunami warning centers that are responsible for issuing tsunami warnings, watches, advisories and information messages to U.S. emergency management officials and the public:
The West Coast/Alaska Tsunami Warning Center, in Palmer, Alaska, warns
Alaska, the West and East coasts of the United States and Canada, and
the Gulf of Mexico.
The Richard H. Hagemeyer Pacific Tsunami Warning Center, in Ewa Beach,
Hawaii, warns U.S. interests and territories throughout the Pacific,
including Hawaii.
In an international role, NOAA's Pacific Tsunami Warning Center serves as the operational center for the Tsunami Warning System of the Pacific, which is comprised of 26 member nations of the Pacific Rim.
In this role, this center issues tsunami warnings for Pacific Basin teletsunamis (tsunamis traveling across the Pacific Ocean). For local tsunamis outside the United States, events which travel only a short distance, the tsunami warnings are issued individually from the nations near the occurrence.
For example, if an earthquake occurs off the coast of Japan and a local tsunami is generated, it is the Japanese government's responsibility to warn its population. If that tsunami were to cause damage far from its source, NOAA's Pacific Tsunami Warning Center notifies participating nations in the Pacific Basin.
If a strong earthquake takes place, the appropriate tsunami warning center will issue a watch or warning that is immediately broadcast over NOAA Weather Radio All-Hazards and through other communications channels, including the Emergency Alert System, NOAA Weather Wire, the Emergency Managers Weather Information Network, and the public via the Internet. Earthquakes of lower magnitudes that are less likely to trigger a tsunami may warrant a less consequential Tsunami Information Bulletin.
Explanations of the different warning products and tsunami terms are below.
Tsunami Product Descriptions:
Tsunami Information Message is issued when small earthquakes are felt to assure coastal residents and emergency managers that there is no tsunami danger.
Tsunami Information Bulletin notes the location and magnitude of the earthquake and provides an evaluation of the potential for a tsunami.
Tsunami Advisory indicates the areas outside of the current warning and watch areas.
Tsunami Watch indicates a tsunami has been detected and could affect all or a portion of a designated area -- meaning the risk of a tsunami has increased, but its occurrence and timing are uncertain.
Tsunami Warning is the highest level of tsunami alert and indicates a tsunami is (occurring, imminent or highly likely) and would contain a call to action, e.g., "move to higher ground" or "monitor NOAA Weather Radio All Hazards."
When appropriate, NOAA may also issue a Tsunami Watch/Warning Cancellation for all or portions of the affected areas.
General Background
* Tsunami (soo-NAH-mee) is a Japanese word meaning "harbor wave." It is a
series of ocean waves created by a sudden displacement of seawater.
* A local tsunami is the result of an earthquake or other water-displacing
event occurring just offshore. People in affected areas may only have
minutes to act.
* Teletsunamis are waves that travel from the source across the open
ocean. These may take several hours to reach affected populations.
Typically, there can be five to 60 minutes between the wave crests. The
first wave may not be the largest. The second wave is often deadlier, as
it carries more debris.
* Most tsunamis are generated by undersea earthquakes, but they can be
caused by other sudden displacements of seawater -- such as submarine
landslides, volcanic eruptions and, in very rare instances, meteor
strikes.
* Not all major earthquakes generate tsunamis. Tsunamis are typically
generated by vertical movement of the sea floor. If the sea floor
movement is horizontal, a tsunami is less likely to be generated.
* Tsunamis travel quickly across the open ocean -- approximately 500 mph
or about the speed of an airliner. As they travel, wave height is
typically less than three feet and nearly undetectable except by
sophisticated instruments, but sharply rises as it nears the shore.
Damage from tsunamis results from the force of the waves, the debris
they carry, and related flooding, fires and other impacts.
On the Web:
NOAA: http://www.noaa.gov
NOAA Tsunami Portal: http://www.noaa.gov/tsunamis.html
CONTACT: Greg Romano of National Oceanic and Atmospheric Administration, +1-301-713-0622, ext. 169, cell: +1-202-360-5992. SOURCE National Oceanic and Atmospheric Administration
