Winds over Japan on Sunday likely to blow radioactivity towards Tokyo

Radioactive plumes emitted from Japan's troubled Fukushima nuclear power plant will remain near the plant or move out to sea today, due to weak offshore winds blowing over the region. On Sunday, an elongated area of low pressure will develop off the southeast coast of Japan, and the counter-clockwise flow of air around this low may bring several periods of north to northeast winds Sunday through Tuesday to Tokyo and northern Japan. According to the latest trajectory plots from NOAA's HYSPLIT model, these winds may be able to transport radioactivity from the Fukushima power plant to Tokyo beginning at 18 UTC on Sunday. The low pressure system will also bring periods of rain to Japan Sunday through Tuesday, and these rains will tend to remove the great majority of the radioactive particles from the air in a few hours, and it is uncertain how much radioactivity might make it to Tokyo. Radiation at the levels being reported coming from the troubled plant are not high enough to be of concern to human heath outside of Japan, so I will not be posting further plots showing the long-range path of the radioactivity unless there is a major explosion resulting in a significant increase in radioactive emissions. From what I've been able to gather from official reports of radioactivity releases from the Fukushima plant, Tokyo will not receive levels of radiation dangerous to human health in the coming days, should emissions continue at current levels.


Figure 1. One-day forecast movement of plumes of radioactive air emitted at 10 meters altitude (red line) and 100 meters (blue line) at 18 UTC (2pm EDT) Sunday, March 20, 2011 from the Fukushima Daiichi nuclear plant. The plumes get caught in northeasterly winds, and move over Tokyo at the surface by 6 UTC on Monday, March 21. This is a low confidence forecast, as winds are expected to be light and somewhat variable on Sunday over Japan. Images created using NOAA's HYSPLIT trajectory model.


Figure 2. One-day forecast movement of plumes of radioactive air emitted at 10 meters altitude (red line) and 100 meters (blue line) at 18 UTC (2pm EDT) Monday, March 21, 2011 from the Fukushima Daiichi nuclear plant. The surface plume moves over Tokyo by 18 UTC on Tuesday, March 22, at an altitude of about 1000 meters, while the plume emitted at 100 meters altitude does not make it to Tokyo, getting caught in a upper-level jet stream of southwesterly winds. This is a low confidence forecast, as winds are expected to be light and somewhat variable on Monday over Japan. Images created using NOAA's HYSPLIT trajectory model.

Resources
Seven-day weather forecast for Sendai near the Fukushima nuclear plant

The Austrian Weather Service is running trajectory models for Japan.

Current radar loops from the Japan Meteorological Agency

I'll have a new post on Monday morning.

Jeff Masters