For the first two days after the accident, the wind blew east from Fukushima towards monitoring stations on the US west coast; on the third day it blew south-west over the Japanese monitoring station at Takasaki, then swung east again. Each day, readings for iodine-131 at Sacramento in California, or at Takasaki, both suggested the same amount of iodine was coming out of Fukushima, says Wotawa: 1.2 to 1.3 × 1017 becquerels per day.Found at newscientist, here.
The agreement between the two "makes us confident that this is accurate", he says. So do similar readings at CTBT stations in Alaska, Hawaii and Montreal, Canada – readings at the latter, at least, show that the emissions have continued.
In the 10 days it burned, Chernobyl put out 1.76 × 1018 becquerels of iodine-131, which amounts to only 50 per cent more per day than has been calculated for Fukushima Daiichi. It is not yet clear how long emissions from the Japanese plant will continue.
However, here in the states, we're safe, as can be seen using this handy map of radiation levels.