In late August, Hurricane Lane narrowly spared Hawaii’s densest and most populous island from widespread damage. But what if it hadn’t?

A new analysis prepared by the Maui-based Pacific Disaster Center estimates how much wreckage Lane would have caused if it had hit Oahu’s southern shore as a Category 1 hurricane instead of breaking apart hours before landfall. The impact, it found, would have been devastating to many Honolulu homeowners.

Under the “what-if” scenario, the tropical cyclone would have displaced 3,800 families on Oahu, leaving those mostly wooden homes either severely damaged or completely destroyed by sustained winds of up to 94 miles per hour.

With roofs torn off, walls ripped away or tree branches and other large debris hitting the homes, they “would be in the ‘destroyed’ and ‘major (damage)’ category,” Doug Bausch, PDC’s science advisor, said Tuesday.

The worst of the damage would have centered around Waikiki, according to the analysis, which was presented at a public meeting about Honolulu’s disaster preparedness on Nov 3.

Overall, Oahu would have suffered some $3.7 billion in damage had Lane made landfall at the lowest level possible for hurricane strength. The vast majority of that damage — 94 percent — would have been inflicted on residential property, according to Bausch.

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“Wind continues to be our No. 1 potential (threat) in terms of losses, specifically to residential,” he said.

Some 2,300 people with nowhere else to stay would have sought long-term public shelter space, PDC found.

The University of Hawaii-affiliated nonprofit research center used HAZUS, a Federal Emergency Management Agency modeling tool, to produce its damage estimate.

The analysis highlights one of Oahu’s most troubling vulnerabilities: Most of its homes risk severe storm damage, state emergency officials say, because they were built before building codes to strengthen against hurricane winds were enacted.

Hawaii is already grappling with a statewide shortage of emergency shelter space. Officials say they’re doing what they can with the money available to retrofit public buildings and play catch-up. But the aging, private homes pose an additional problem.

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“We can retrofit a shelter space eventually that may fit you, but what are you going to go home to afterward?” said Jennifer Walter, a preparedness branch chief at the Hawaii Emergency Management Agency. “We get very fixated on the period when the storm is hitting, but imagine the recovery if all those homes are gone.”

Prior to the mid-1990s, “single-wall” construction dominated Oahu home-building, officials say. It’s a lighter construction method that still largely defines many of Honolulu’s older neighborhoods.

Bausch estimates that one in five single-wall construction homes without any hurricane retrofits on Oahu would not survive a Category 2 storm.

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Homes built on Oahu prior to 1995 also generally lacked what’s known as a “continuous load path,” where the roof is firmly tied to the walls and the walls are then firmly tied to the foundation in order to better withstand being torn apart by severe winds.

Nearly 189,000 housing units were built statewide between 1940 and 1995, according to HI-EMA officials, who also used FEMA’s HAZUS tool to get that data.

On Tuesday, Bausch provided data showing more than 185,000 wooden homes currently stand on Oahu.

Retrofits Could Save Older Homes

Many local homeowners have retrofitted their pre-1995 properties, however, to provide better shelter against a storm as strong as a Category 2 hurricane.

“We encourage everyone to strengthen their house,” said Dennis Hwang, a coastal hazard mitigation specialist at the University of Hawaii’s Sea Grant College Program. Hwang is among the state’s strongest advocates pushing for home retrofits, and he co-authored a free downloadable handbook for those looking to better protect their homes.

Such retrofits can only go so far with the island’s oldest homes, however. Even with hurricane clips and reinforced foundations, many single-wall construction homes likely would not survive more than a Category 2 storm, Hwang said.

“You can only make it so strong. It’s hard to make a 60-year-old as strong as a 20-year-old person,” he said.

But they could become as strong as a 40-year-old, he added. The same idea goes for single-wall construction, Hwang said.

With Hawaii’s unique topography, a Category 1 hurricane could actually whip peak gusts as strong as a Category 4 storm across the the island’s ridges and valleys, leaving the homes in those corridors even more vulnerable, Bausch said.

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Hwang also created a custom table for Hawaii residents to better decide whether to shelter-in-place or head to an emergency shelter based on the condition of their house. As more homes get retrofitted, fewer residents potentially would require public shelter space — helping to ease the strain.

Should a hurricane ever bring widespread devastation to Oahu, FEMA trailers would not be an option. “They’re extremely expensive to transport,” said Dolph Diemont, a FEMA federal coordinating officer.

Hawaii’s remote, isolated location poses a unique challenge. Unlike on the U.S. mainland, “you can’t just pull things over the state line and have things stood up,” Walter said. “It just becomes very complex logistically.”

FEMA is currently weighing alternatives to those trailers, however, such as temporary, “modular” homes and converted shipping container spaces that might provide shelter to displaced families instead.

“When you have a complex problem like this, it’s very tempting to try and find that silver bullet that’s going to address it,” Walter said of the state’s ongoing shelter woes. “You see a lot of attention on these issues after something’s happened. What gets really hard is keeping that attention and the funding going when it’s been several years.

Here’s a copy of the Pacific Disaster Center’s presentation: