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What is the difference between a tsunami Watch, Advisory and Warning?
Tsunami Warning:
A “Warning” is the highest level of tsunami alert. Warnings are issued 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 harbours to deep waters. Warnings are updated at least hourly, or as conditions warrant, to continue, expand, restrict or end the Warning.
Tsunami Advisory
An “Advisory” is the second highest level of tsunami alert. Advisories are issued due to the threat of a tsunami that has the potential to produce strong currents dangerous to those in or near the water. Significant inundation is not expected for areas under an Advisory, but coastal zones may be at risk due to strong currents. Appropriate actions by emergency management personnel may include closing beaches and evacuating harbours and marinas. Additionally, local officials may opt to move boats out of harbours to deep waters, if there is time to safely do so.
Tsunami Watch
A “Watch” is the third highest level of tsunami alert. Watches are an advance alert that, based on an analysis of the event, may be cancelled or upgraded to a Warning or Advisory prior to impact. There is a potential threat to a zone contained in a Watch but communities have time to prepare. Watches are normally based on seismic information, without confirmation that a destructive tsunami is underway. Emergency management personnel and coastal residents should prepare to take action in case the Watch is upgraded