The massive earthquake with preliminary magnitude 8.9 that occurred near the east coast of Honshu, Japan at 12:46 am EST has triggered a major tsunami. This tsunami will eventually be felt over much of the Pacific and has the potential for large loss of life.
The above graphic provided by NOAA shows the forecast travel times of the tsunami as it propagates out from the area of the earthquake. You can see that much of the Pacific will feel at least some impact.
Tsunamis have similarities with hurricanes, but there are also significant differences. The main thing in common is the tremendous rise in water level at the coastline. While the storm surge is more like a dome of water that starts coming in gradually and then rises more quickly near the hurricane’s landfall, the tsunami is a series of long ocean waves. Each individual wave crest can last 5 to 15 minutes or more and extensively flood coastal areas. The danger can continue for many hours after the initial wave as subsequent waves arrive. It is important to note that the first wave may not be the largest. Tsunami waves efficiently wrap around islands and all shores are at risk no matter which dirrection they face.
See the animation at http://staff.washington.edu/liujuan/tsunami/20110311/20110311Houshu.mov to follow the tsunami as it moves across the Pacific.
The National Weather Service operates two Tsunami Warning Centers, the West Coast/Alaska Tsunami Warning Center and the Pacific Tsunami Warning Center that provides guidance for all U.S. coastal states (except Hawaii) and the Richard H. Hagemeyer Pacific Tsunami Warning Center that provides guidance for Hawaii and countries in the Pacific Ocean, Indian Ocean, and Caribbean Sea. Specific tsunamis warnings can be found at www.tsunami.gov and, for U.S. interests,currently include the Hawaiian Islands, portions of the U.S. west coast, and the American territories in the Pacific.
People in the tsunami warning areas should heed the advice of their local officials. I often tell people in hurricane storm surge vulnerable areas to make friends in high places. That advice applies to people told to evacuate from the tsunami as well. People in the tsunami warning coastal areas should move inland to higher ground if told to do so by their local officials.