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Tsunami Warning/Advisory and Tsunami Information

After an earthquake occurs, the Japan Meteorological Agency (JMA) issues Tsunami Warnings/Advisories and Tsunami Information bulletins if a tsunami strike is expected.
Major Tsunami Warnings are issued in the classification of Emergency Warnings as of 30 August, 2013.

 

Tsunami Warning/Advisory

When an earthquake occurs that could generate a disastrous tsunami in coastal regions of Japan, JMA issues Major Tsunami Warnings, Tsunami Warnings and/or Tsunami Advisories for individual regions based on estimated tsunami heights around three minutes after the quake (or as early as two minutes in some cases*).
Immediately after an earthquake occurs, JMA promptly establishes its location, magnitude and the related tsunami risk. However, it takes time to determine the exact scale of earthquakes with a magnitude of 8 or more. In such cases, JMA issues an initial warning based on the predefined maximum magnitude to avoid underestimation.
When such values are used, estimated maximum tsunami heights are expressed in qualitative terms such as "Huge" and "High" in initial warnings rather than as quantitative expressions. Once the exact magnitude is determined, JMA updates the warning with estimated maximum tsunami heights expressed in quantitative terms.

* Earthquakes in and around Japan to which JMA can apply the Earthquake Early Warning technique to promptly and accurately determine the hypocenter and magnitude

Category Indication Estimated maximum tsunami heights Expected damages and actions to be taken
Quantitative
expression
Qualitative
expression
Major Tsunami Warning** Tsunami height is expected to be greater than 3 meters. over 10 m
10 m
5 m
Huge Wooden structures are expected to be completely destroyed and/or washed away; anybody exposed will be caught in tsunami currents.
Evacuate from coastal or river areas immediately to safer places such as high ground or a tsunami evacuation building.
Tsunami Warning Tsunami height is expected to be up to 3 meters. 3 m High Tsunami waves will hit, causing damage to low-lying areas. Buildings will be flooded and anybody exposed will be caught in tsunami currents.
Evacuate from coastal or river areas immediately to safer places such as high ground or a tsunami evacuation building.
Tsunami Advisory Tsunami height is expected to be up to 1 meter. 1 m N/A Anybody exposed will be caught in strong tsunami currents in the sea. Fish farming facilities will be washed away and small vessels may capsize.
Get out of the water and leave coastal areas immediately.

** Major Tsunami Warnings are issued in the classification of Emergency Warnings.
Detailed information on Emergency Warnings is provided on the Emergency Warning System web page.


Note
  • Tsunamis may hit before warnings are issued if the source region is near the coast. Be sure to evacuate when strong shaking or weak ground motion continuing for an extended period occurs.

  • If a Major Tsunami Warning with the quantitative term "Huge" is issued, tsunamis as large as those seen after the Great East Japan Earthquake of 2011 may hit. Evacuate immediately to the safest place possible.

  • Tsunami heights may exceed estimates due to coastal topography and other factors in some regions. Do not assume you are in a safe place; keep evacuating to higher and higher ground wherever possible.

  • Tsunami waves are expected to hit repeatedly. Do not leave the tsunami evacuation location until Tsunami Warnings are cleared.

 

Tsunami Information

When Tsunami Warnings and/or Advisories are issued, Tsunami Information bulletins on matters such as estimated tsunami heights and arrival times are subsequently issued.
Messages about tsunami Indication
Tsunami Information
(Estimated Tsunami Arrival Time and Height)
Estimated arrival times* and heights of the tsunami for relevant tsunami forecast regions.

* The estimated tsunami arrival time for each tsunami forecast region is the time at which it is expected to hit first in any part of that area. Hence, in some coastal regions, tsunamis may hit after the estimated time.
Tsunami Information
(High Tide Time and Estimated Tsunami Arrival Time at each place)
The high tide times and estimated arrival times of the tsunami at selected points.
Tsunami Information (*1)
(Tsunami Observations)
Arrival times and heights of the tsunami observed at tide gauges or tsunami meters.
Tsunami Information (*2)
(Tsunami Observations at Offshore Gauges)
Tsunami arrival times and heights observed at offshore gauges, and related tsunami heights along the coast in the corresponding forecast region estimated from offshore observations.

 

(*1) Issuance of Tsunami Information based on Tsunami Observations

Example of Tsunami Information on Tsunami Observations


JMA announces the arrival times and initial movement of the first observed waves in coastal areas, and also provides information on the arrival times and scale of the highest waves observed as of the time of issuance.
As tsunami waves can hit repeatedly and those arriving later may be higher, it is inadvisable to abandon evacuation if the initially observed waves are small. Accordingly, when a Major Tsunami Warning and/or a Tsunami Warning is in effect and observed tsunamis appear much smaller than estimated, JMA uses the phrase "Currently Observing" rather than actual values to keep people aware that higher waves may still approach.

Expressions used for observed maximum heights in coastal areas
Warnings/advisories in effect Observed heights Information bulletin expressions
Major Tsunami Warning Height > 1 m Actual values
Height ≦ 1 m "Currently Observing" announcements
Tsunami Warning Height ≧ 0.2 m Actual values
Height < 0.2 m "Currently Observing" announcements
Tsunami Advisory (all cases) Actual values
("Slight" for very small waves)

 

(*2) Issuance of Tsunami Information based on Tsunami Observations at Offshore Gauges

Example of Tsunami Information on Tsunami Observations at Offshore Gauges


JMA announces the arrival times and initial movements of the first observed waves offshore, and also provides information on the arrival times and scale of the highest waves observed as of the time of issuance. JMA also announces estimated data for tsunami waves in coastal areas* (arrival times of initial waves and arrival times/heights of maximum waves) for each tsunami forecast region expected to be affected.

JMA does not provide actual values for observed tsunami heights offshore or estimated maximum tsunami heights for coastal areas until the thresholds for issuance are reached (in the same way as those for coastal areas) in consideration of the related influence on people's evacuation. When a Major Tsunami Warning and/or a Tsunami Warning is in effect and estimated tsunami heights for coastal areas are small, JMA uses the phrase "Currently Observing" for observed heights offshore and "Currently Investigating" for estimated heights in coastal areas to keep people aware that higher waves may still approach.

Expressions used for observed maximum heights at offshore gauges and estimated maximum heights in coastal areas*
Warnings/advisories in effect Estimated tsunami heights for coastal areas Information bulletin expressions
Major Tsunami Warning Height > 3 m Actual values for observed heights at offshore gauges and estimated heights in coastal areas
Height ≦ 3 m "Currently Observing" for offshore observations and "Currently Investigating" for estimated heights in coastal areas
Tsunami Warning Height > 1 m Actual values for observed heights at offshore gauges and estimated heights in coastal areas
Height ≦ 1 m "Currently Observing" for offshore observations and "Currently Investigating" for estimated heights in coastal areas
Tsunami Advisory (all cases) Actual values for observed heights at offshore gauges and estimated heights in coastal areas

* For gauges more than 100 km offshore, JMA does not announce the relevant estimated tsunami heights for coastal areas due to the difficulty of determining which tsunami forecast regions waves will reach from offshore gauges. Announcement of tsunami heights observed at such gauges is begun when JMA issues an information bulletin detailing actual values for observed and estimated heights from other offshore gauges closer to the coast. Until this time, the phrase "Currently Observing" is used.

 

Tsunami Forecast

After an earthquake occurs, if no damage is expected, JMA issues Tsunami Forecasts.

Forecasted sea level changes Message
No tsunami is expected "No tsunami is expected." (To be included in Earthquake Information.)
Tsunami height less than 0.2 meters is expected No damage is expected because sea level changes will be less than 0.2 m, and no special action is needed.
Slight sea level changes are expected to continue
after Tsunami Warnings/advisories are cleared
Particular attention is needed when fishing, swimming or engaging in other marine activities because tsunami-related sea level changes have been observed and may continue for a while.