Despite the Meteorological Agency’s alerts for an “extraordinary situation” anticipated from powerful Typhoon Wipha, no evacuation advisory was issued on Izu-Oshima, a small island south of Tokyo in the Pacific, where at least 22 people were killed and dozens remain missing.

The failure to get residents to safety has angered those who lost their homes and has left many questions to address about the steps authorities took to issue warnings.

The Meteorological Agency has established yardsticks for issuing special warnings to municipalities when “once in 50 years” heavy rain is forecast — for periods of three hours and 48 hours.

In the town of Oshima, which covers the entire island with a population of just over 8,300, the thresholds were 147 mm in three hours and 419 mm in 48. Precipitation drastically exceeded both thresholds with rainfall through Wednesday morning hitting 335 mm in three hours and 824 mm in 24 hours.

Around 4 a.m. Wednesday, the agency confirmed that rainfall had reached the threshold for the three-hour window but did not announce it, considering it a localized phenomenon not meeting the conditions for issuing a special warning.

The conditions require concurrent threshold-level rainfall in at least 10 locations in an “area comparable to a prefecture,” according to the agency. “Given the amount of damage done, we need to examine what went wrong,” an official in charge of the matter said.

Even if a special warning had been issued, it was still dark around 4 a.m. Wednesday and evacuations would have been difficult in the ferocious rain. Also, the mudslides that hit the town’s Motomachi district had already occurred about an hour earlier.

At 11:30 p.m. Tuesday, a weather agency official called an official at the Tokyo Metropolitan Government’s river department, saying it was “possible that an extraordinary situation could develop.” At 91 sq. km, Izu-Oshima is the biggest of the Izu chain of islands under Tokyo’s jurisdiction.

In addition to issuing alerts for heavy rain and mudslides, the agency said it expressed its concern to the metro government and the town.

At 1:35 a.m. Wednesday, the agency told Tokyo’s disaster preparedness division that rainfall was exceeding 400 mm in a 24-hour period and that the situation was becoming “extraordinary.”

The division said it passed the information on to the town but did not sound out officials there about issuing an advisory.

“The damage was concentrated in the town center, which does not have a steep slope,” a senior Tokyo metropolitan official said.

“We didn’t think there would be a landslide. It was difficult to pin down an area for issuing an evacuation advisory.”

Another official said, “We couldn’t anticipate rainfall of this level.”

“The sound of heavy rain was overwhelming,” said resident Kazunori Takeda, 41. “We couldn’t hear anything, including the disaster information announcement.”

He said he was caught in the mudslide while he was driving to work, but he did not sense any danger until immediately before it happened and that it occurred in a second.

Town officials shifted to emergency mode around 2 a.m. “The wind and rain were too strong to order residents to evacuate. It was dangerous to go outside,” one of the officials said.

The town gave up on issuing an evacuation advisory and urged residents at 3:30 a.m. to be aware of river flooding via the disaster information system and other methods.

The town has a rule for issuing evacuation orders in its disaster preparedness plan, saying they should be issued “when there is an imminent danger of mudslides as a result of heavy rain.” But this rule was not apparently used this time.

At 12:30 a.m. Wednesday, the island of Kozu, also part of the Izu Islands, issued an evacuation advisory.

“I don’t know why the town of Oshima couldn’t evacuate its residents,” said Motoyuki Ushiyama, a professor of disaster information science at the Center for Integrated Research and Education of Natural Hazards at Shizuoka University. “It is best to evacuate people in advance, but even when it’s late at night it’s better to get people as far as possible to take refuge in a safe place, such as an area away from cliffs.”

On special heavy rain warnings, Ushiyama said that while in theory they are issued for very violent rain affecting a wide area, “there is room for consideration about what to do with a remote island with a limited area that makes it difficult to issue them.”