In fact, the winds had been blowing directly toward Tsushima – and town officials would learn two months later that a government computer system designed to predict the spread of radioactive releases had been showing just that.
But the forecasts were left unpublicised by bureaucrats in Tokyo, operating in a culture that sought to avoid responsibility and, above all, criticism.
Speaking from Nihonmatsu, where thousands of people from Namie are now living in temporary housing, Namie’s mayor, Tamotsu Baba, said: “We were in a location with one of the highest levels of radiation. We are extremely worried about internal exposure to radiation.”
Withholding the information, he said, was akin to “murder”.
Seiki Soramoto, a MP and former nuclear engineer who advised prime minister Naoto Kan after the Fukushima disaster, blamed the government for withholding the forecasts from the computer system, known as the System for Prediction of Environmental Emergency Dose Information, or Speedi.
“In the end, it was the prime minister’s office that hid the Speedi data,” Mr Soramoto said. “Because they didn’t have the knowledge to know what the data meant, and thus they did not know what to say to the public, they thought only of their own safety, and decided it was easier just not to announce it.”
Goshi Hosono, the minister in charge of the nuclear crisis, said the information was not disclosed because the data was incomplete and inaccurate. He said he was presented with the data for the first time on 23 March.
“On that day, we made them public,” he said. “In the days before that, which were a matter of life and death for Japan as a nation, I wasn’t taking part in what was happening with Speedi.”
Speedi was designed in the 1980s to make forecasts of radiation dispersal that, according to the prime minister’s office’s nuclear disaster manuals, were supposed to be made available to local officials and rescue workers in order to guide evacuees away from radioactive plumes.
Speedi had been churning out maps and other data on an hourly basis since the catastrophic earthquake and tsunami. But the education ministry had not provided the data to the prime minister’s office because it said the information was incomplete.
In fact, the ministry had done just that, running simulations on Speedi computers of radiation releases. Some of the Speedi maps clearly showed a plume of nuclear contamination extending to the north-west of the plant, beyond the areas that were initially evacuated.
Mr Hosono has admitted that certain information, including the Speedi data, was withheld for fear of “creating a panic”.
But he has also said that the government had “changed its thinking” and was trying to release information as fast as possible to the public.