Washington, D.C. -- Scientists estimate roughly 1 1/2 million tons of Japanese tsunami debris is floating in the Pacific Ocean.

Computer models show that lighter pieces of debris, affected by the wind, move faster than heavy debris. Thousands of items, likely from the 2011 tsunami in Japan, have already washed ashore in the U.S. and Canada.

There's potentially still a lot to come, we just don't know, said Nancy Wallace, Director of Marine Debris Program at the National Oceanic and Atmospheric Administration.

NOAA estimates the largest concentration of tsunami debris is floating between Hawaii and the west coast of the United States.

Scientists don't know exactly where it will land or when. Some debris may never wash ashore.

You know in the old days, people would throw a message in a bottle, and you never knew where they were going to come to. And that's kind of what we are dealing with here, just on a really large scale, said Wallace.

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