The first and most important warning sign for a tsunami is an earthquake of enough magnitude that it displaces the water in the ocean, creating large waves. The earthquake occurs on the ocean floor. The tsunami could also be caused by an underwater volcano eruption or landslide.
If you happen to notice the water level of the ocean receding rapidly, that is an indication a tsunami is on the way and should be at the shore within five minutes. The best course of action at this point is to get to high ground as soon as possible.
The rapidly retreating waters are usually accompanied by a loud roaring sound. The noise sounds like a jet plane. The tsunami is approaching. Run as fast as you can to higher ground.
