Hawaii has ratcheted up its planning for a possible — but still very unlikely — North Korean nuclear attack on the isles to 100 kiloton yield from 15 kiloton as the threat from the rogue nation seems to escalate by the week.

The Associated Press reported Thursday that Kim Jong Un may detonate a hydrogen bomb in the Pacific, while Kim Dong-yub, a former South Korean military official, suggested the North may fire a Hwasong-14 intercontinental ballistic missile out to 7,000 kilometers (4,349 miles) to demonstrate it can hit Hawaii or Alaska.

The news came on the same day that the Hawaii Emergency Management Agency held a briefing for the public at the state Capitol on its North Korea preparedness plan, which is still being developed. About 75 people attended.

The missile threat from North Korea “is still unlikely,” agency Administrator Vern Miyagi said. “But it’s the elephant in the room. We can’t ignore it. We have to address it.”

The fact that Hawaii no longer has designated fallout shelters didn’t sit well with Nick LaCarra of Ewa Beach.

“With our longstanding history of hurricanes and the destruction that’s currently going on and now this imminent threat from North Korea — how is it we don’t have fallout shelters for our citizens?” LaCarra asked during a question-and-answer session.

Miyagi said Oahu as late as the 1990s had hundreds of designated shelters, some with medical supplies and food.

“But as the Cold War died, as the Iron Curtain came down, the Soviet Union turned into Russia and there was no threat anymore, the funding ran out,” Miyagi said.

With the state population doubling, hurricane shelters are also in short supply, he said. “It takes a lot of money to expand the shelter program,” Miyagi said.

He also emphasized that the time it would take for a North Korean missile to reach Hawaii would be 20 minutes. With such a short warning time, the state’s advice is “get inside, stay inside, and stay tuned” for radio instructions.

“Sometimes, I hear criticism about this. It’s like — that’s it?” Miyagi said. “When you have 20 minutes, this is what we need to do.” Fallout shelters during the Cold War were seen as refuges if relations with the Soviet Union started heating to the boiling point, providing some lead time. After U.S. Pacific Command warns Hawaii Emergency Management that a missile is on its way, only 12 to 15 minutes theoretically would be left to warn the public.

Original state planning contemplated the remote possibility of a 15-kiloton North Korean nuke — about the size of the Hiroshima blast — detonating somewhere in Hawaii. But on Sept. 3, North Korea detonated its most powerful device ever. U.S. intelligence estimates placed the yield at more than 100 kilotons.

Miyagi said Hawaii Emergency Management recalculated the potential effects of a 100-kiloton bomb on Hawaii after that. Detonated at 1,000 feet, the device would have a blast zone of 3 to 4 miles, officials said. More recently, the North Korea monitoring site 38North.org said the Sept. 3 yield could have been 250 kilotons.

Miyagi also said that the Nov. 1 inauguration of a wavering air raid siren test, to prepare for a North Korean attack, has been postponed. A throwback to air raid warnings of World War II and not heard in Hawaii since the Cold War, the wavering siren is planned to be paired with the regular monthly “attention alert” steady tone test on the first business day of each month at 11:45 a.m. that’s mainly for hurricanes or tsunamis.

“We need to work things out with the counties,” Miyagi said after the meeting. “When they took it (the attack siren) out to the counties, there was concern whether the two siren sounds would cause confusion or misunderstanding — because we’re so used to the single siren sound.”

“So we want to make sure that we have complete buy-in from the counties and we do it the right way ahead of time,” Miyagi added.

He also said that the agency is “still preparing that product — that (attack warning) siren capability.” No firm date has been set for the new statewide siren test.

Marie Iding asked how the state plans to deal with drivers on roads and highways in the event of an attack. Toby Clairmont, executive officer for Hawaii Emergency Management, said the advice is to get out of the car and seek shelter or lie flat on the ground.

“There are going to be people on the road. It’s going to be chaotic. They’ll probably bang (into) each other in the process,” he said. One questioner raised concern about the nuclear reactors in the 20 attack submarines that are based at Pearl Harbor.

A state suggestion was for “safe rooms” to be built in homes.

“Are you expecting the public to do this? Take it on themselves in their own home?” asked LaCarra. The answer was yes.

Outside the meeting Iding said that with North Korea’s growing nuclear expertise, “we should think about preparation. It’s a reasonable thing.”

“I’m not here out of fear that it (an attack) is going to happen anytime soon,” she added. “I think it’s something we should be aware of.”