The plume is anticipated to remain over the ocean, moving toward the southeast and then south through the afternoon of Monday April 4 Japan Standard Time (JST).
An illustration of the variability in coastal conditions that can lead to high forecast sensitivity occurred on the night of Saturday April 2 (JST). The prior day’s forecast (discussed in the post for 4/3) showed the plume bifurcating near the source, with the southern extension moving along the coast for a bit and then over the ocean. The forecast initiated 36 hours later covers the same time period and is generally taken to be more accurate because it is able to ingest local observations closer to the forecast time, using a sophisticated data-assimilation algorithm. This later forecast produced maps showing the plume moving south over land above the city of Choshi as the evening progressed (see top panels below). Similarly, the revised forecast for March 23 (see 3/24 post) showed this same region impacted when the earlier forecast did not project the plume to move in that direction. This might be an area to look for potential elevated levels of radiation, if there were indeed controlled or uncontrolled releases around these times.
Releases may be continuing in association with localized criticality in reactor 1 which is believed to have experienced meltdown in 70% of the core. In addition, the release of steam through the “feed-and-bleed” strategy is an additional source of airborne release that is occurring intermittently now at several reactors.
The Naval Research Laboratory’s 5 km resolution data-assimilating meteorological model COAMPS produced the fields below, using a passive tracer to map the expected plume trajectory. Lighter gray contours show more concentrated material. [Plume images are a research tool; contours are arbitrary units for visualization purposes.]