What warnings are given out when a tsunami is coming?

Here is my final answer for What warnings are given out when a tsunami is coming?

All oceans and most countries near oceans have a tsunami warning system. A tsunami warning system does three things.
1. It has a seismic monitoring network to detect seismic activity like earthquakes and a sea level monitoring network to detect sea level changes that may indicate a tsunami.
2. It has software to scientifically model the size, arrival time and impact points of the tsunami generated by the seismic event.
3. It has an established system for issuing warnings to emergency services and the general public in the affected areas about the approaching tsunamis.