About 25 million tons of Japanese tsunami debris - boats, pieces of smashed buildings, appliances, and plastic, metal, and rubber objects of all shapes and sizes - may end in the U. S. shores, NOAA scientists said.

NOAA, which has captured satellite images of the debris which are either sinking near the shore or floating out to sea, is now coordinating an interagency assessment and response plan to address the effects and threats posed by the debris.

According to computer models run by NOAA and University of Hawaii researchers, some debris could pass near or wash ashore in the Northwestern Hawaiian Islands as early as this winter, approach the West Coast of the United States and Canada in 2013, and circle back to the main Hawaiian Islands in 2014 through 2016.

The Japanese government has estimated about 25 million tons of rubble from the tsunami, but exactly how much debris was swept into the water nor what remained afloat is not known. After nine months the debris, which has been scattered by winds and ocean currents, are no longer visible from satellite. Researchers said that models are only predictions based on location of debris when it went into the water, combined with historical ocean currents and wind speeds.

"We're preparing for the best and worst case scenarios - and everything in between," says Nancy Wallace, director for NOAA's Marine Debris Program.

In a worst-case scenario, boats and unmanageable concentrations of other heavy objects could wash ashore in sensitive areas, damage coral reefs, or interfere with navigation in Hawaii and along the U.S. West Coast, scientists said.

In a best case scenario, the debris will break up, disperse and eventually degrade, sparing coastal areas, the NOAA said, but even in this scenario, the debris will not go away completely.

Even now, marine debris is problem for Hawaii and West Coast states, where garbage and other harmful items regularly wash up on beaches, reefs and other coastal areas.

An interagency reporting and monitoring system led by NOAA will provide critical information on the location of the marine debris generated by the tsunami. Anyone who observes significant at-sea debris sightings can request shoreline monitoring guides at DisasterDebris@noaa.gov.