There are traditional and fairly well-known warning signs that a tsunami will hit. A little girl on vacation on an Island during the Asia Pacific tsunami saved about a hundred lives by paying attention to these and a few less well-known warning tsunami signs. She shared them with her parents who warned others. They all evacuated immediately and it saved their lives. Over 200,000 other people died in that tsunami.
The usual signs to look for are:
There is a sudden low tide that is not expected.
The ocean withdraws suddenly. Some people report a "sucking" noise as the ocean retreats.
The girl who saved 100 lives, noticed strange froth on the ocean and a "sizzling" noise coming from the froth.
Sea birds often fly inland and refuse to land.
Elephants headed inland before the Asian Pacific tsunami. They crashed into things in their haste.
Some of the people who died in that tsunami were down on the beach catching flopping grounded fish, or examining the exposed sea bed.
You do not have a long time before the wave from a withdrawn sea, getting ready for a tsunami, comes back and hits. When you see the ocean suddenly retreat you have to move fast to higher ground to save your life. Tsunamis are very fast. You will not be able to outrun the tsunami if you wait until you see it coming.
I took these from a site that helps you live through tsunamis: