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 damage and action 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.

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.