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Tsunami Advisory, Watch, and Warning Definitions
The tsunami product definitions in NWS Instruction 10-701, including the stated hazard and inundation language.
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Updated: Sources: 1
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What matters now
- A tsunami advisory is issued when the stated dangerous-current or wave hazard is imminent, expected, or occurring.
- A tsunami watch is normally issued from seismic information without confirmation that a destructive tsunami is underway.
- A tsunami warning is issued when widespread inundation is imminent, expected, or occurring.
- Advisories allow dangerous currents or waves but not significant inundation.
NWS Instruction 10-701 defines tsunami watch, advisory, and warning products with different stated hazard and inundation language. This article reports those definitions and does not determine conditions for a particular coastline.
This original record-reading guide is a general reading aid, not cited evidence. It does not depict a source record; the article text and source links provide the facts.
What a tsunami watch means
A tsunami watch is defined in NWS Instruction 10-701 as an alert to emergency management officials and the public of an event that may later impact the watch area.
It goes on to explain why a watch carries less certainty than an advisory or warning: “Watches are normally issued based on seismic information without confirmation that a destructive tsunami is underway.” (same source) A watch is a heads-up issued from earthquake data alone, before anyone has confirmed that a hazardous tsunami actually exists.
What a tsunami advisory means
NWS Instruction 10-701 defines the advisory this way: “A tsunami advisory is issued when a tsunami with the potential to generate strong currents or waves dangerous to those in or very near the water is imminent, expected, or occurring.”
The same definition draws a boundary on how bad the flooding is expected to be: “but significant inundation is not expected for areas under an advisory.” (same source) In other words, an advisory confirms a real hazard to people in or very near the water — dangerous currents and waves — without the widespread inland flooding that defines the more severe warning level.
What a tsunami warning means
The instruction states: “A tsunami warning is issued when a tsunami with the potential to generate widespread inundation is imminent, expected, or occurring.” (NWSI 10-701)
Two other tsunami products
NWS Instruction 10-701 also defines two related products that round out the tsunami messaging system. A tsunami information statement is used to stand down concern rather than raise it: “In most cases, information statements are issued to indicate there is no threat of a destructive basin-wide tsunami and to prevent unnecessary evacuations.”
And once a hazard has passed, NWS issues a distinct closing product: “This is a final product indicating the end of the damaging tsunami threat.” (same source)
About this directive
This explainer draws on the current, official version of the governing document: “NATIONAL WEATHER SERVICE INSTRUCTION 10-701,” dated “JANUARY 6, 2022,” with office of primary responsibility “OPR: W/AFS26 (S.Rogowski)” and “Certified by: W/AFS26 (G. Schoor).” (NWS Instruction 10-701) The version referenced here is administrative in nature — “Type of Issuance: Routine – Admin Update” — and the document itself notes the scope of that update: “This is an administrative update made only to change all references of ‘Gulf of Mexico’ to ‘Gulf of America.’ No content changes were made with this update, and the effective date was not affected.” (same source) The advisory, warning, and watch definitions quoted above were not altered by that update.
Source links
https://www.weather.gov/media/directives/010_pdfs/pd01007001curr.pdf