What Would Happen if a Category 4 Hurricane Hit Oahu?

On Kauai in 1992, it took four months to fully restore power, water and phone service after Iniki. What would it look like if such a hurricane hit Oahu?

By David Thompson

Image: Wikipedia

What if a Category 4 hurricane like Hurricane Iniki, which tore Kauai apart in 1992, hit Honolulu? That’s exactly the scenario Hawaii’s emergency-management officials and researchers use for disaster planning, and, after talking with them and looking at their hazard mitigation studies and plans, the answer is clear: We’d be screwed. Or as Karl Kim, a disaster researcher at UH’s Department of Urban and Regional Planning, puts it, “If Iniki had hit the south shore of Oahu, there would be potential for thousands of people to be killed, and there would be billions of dollars worth of damage.”

While Iniki-strength hurricanes come ashore with sustained winds of 131 to 155 miles per hour, wind models show Oahu’s mountainous terrain would amplify speeds to as much 200 miles per hour in some areas. A high percentage of Oahu’s wood-framed homes, most of them built to hurricane resistance standards that are no longer considered adequate, would be demolished. Roofs are always the first things to go, then walls separate and blow away and, before you know it, whole neighborhoods are flattened. Residentially developed ridgelines, exposed to some of the strongest winds, could be wiped clean.

In town, clusters of high-rises would create funnel effects that also amplify the wind. The upper floors of the tallest buildings would sway crazily, but the buildings wouldn’t fall. The lower floors would sustain the greatest damage from windborne debris. Tree branches, coconuts, two-by-fours, gravel, solar paneling and all sorts of other objects would be transformed into projectiles. Trees and power poles alike would be blown down across the island. The resulting blackout would be total and long-lasting. On Kauai, it took four months to fully restore power, water and phone service after Iniki. No one can say how long it would take on Oahu, but the job would be massive.

Along the coast, storm surge would cause massive erosion, wash out highways and damage or destroy homes. Low-lying areas such as Waikiki and Mapunapuna would be swamped. Intense rainfall would touch off rock falls and landslides, which could damage homes and bury roads already blocked by massive amounts of debris. Streams would overflow their banks and course through neighborhoods, sweeping away loose items, like cars.

Oahu’s emergency hurricane shelters have space for about 30 percent of the island’s 1 million residents. Everybody else would be on their own. After the storm, don’t count on Safeway or Whole Foods to be there anymore, and don’t count on seeing policemen, firemen or anyone else from the government anytime soon. “You’ve got to be ready to help yourself and your family for seven days at the minimum,” says John Cummings, public information officer for the city’s Department of Emergency Services. “It’s not that we don’t want to be there, but with a population of a million people, it’s going to be a long time before you see assistance in your community.”

This article originally ran in an October 2013 feature about disaster preparation.