What is the first sign that a tsunami is approaching a shore?

The first sign that a tsunami is approaching shore is often a noticeable and sudden retreat of the ocean water, exposing the ocean floor and reefs. This phenomenon occurs as the tsunami pulls water back before the wave arrives. Additionally, a loud roar or rumble from the ocean may be heard, signaling the impending danger. It's crucial for people in coastal areas to recognize these signs and evacuate immediately.