The West Coast of North America can expect contamination "as early as 2014 and peak in 2016"
This is the first major news source I've come across addressing the speculation. The researcher quoted in the article is Vincent Rossi, an oceanographer and postdoctoral research fellow at the Institute for Cross-Disciplinary Physics and Complex Systems in Spain. "Rossi worked with former colleagues at the Climate Change Research Center at the University of New South Wales in Australia to simulate the spread of Fukushima’s radioactivity in the oceans — a study detailed in the October issue of the journal Deep-Sea Research Part 1".
Based on their research, waters 180 miles off the West Coast may experience an additional "10-30 becquerels per cubic meter of cesium-137", or .01-.03 becquerels per liter. Before everyone runs off to panic, the U.S. EPA limit for radioactive cesium in drinking water is 200 picocuries per liter, which converts to (7.41 Bq/L). Given that we all don't dwell in the ocean every minute of the year - and even if we did - the additional radiation would result in an absurdly miniscule increase to the general population's yearly maximum permissible dose.
Based on available info and the leaks accounted for in Dai-chi, It's difficult to make an argument that Fukushima ocean spillage will adversely affect the health of people living in North America. However, Tepco must get a handle on the problem and find a sustainable solution. Future leaks with higher concentrations of radioisotopes, a massive volume leak, and contamination for years to come may bump concentrations up to the point where it will register in tuna and other fish caught in the open pacific.
Keep an eye on the Hawaii Department of Health's website for an early warning into ocean water and fish contamination levels spreading across the Pacific. Interestingly enough, as of August 16 of this year, the Hawaii DOH has "no near-term plans to test", and "does not anticipate contamination of living marine resources in U.S. waters at this time. For this reason, sampling of U.S. harvested seafood is not currently planned".