Tsunami Warning Signs Could Be Coming to South Seattle in 2027

Ask most people in Seattle about tsunamis, and they'll point west, toward the outer coast. Long Beach. Westport. La Push. Places with sirens, evacuation towers, and blue-and-white signs pointing uphill.

Puget Sound feels safer, tucked behind the Olympic Peninsula and a scatter of islands. The science says otherwise, and starting next year, Seattle's streets will too.

The Seattle Department of Transportation (SDOT) plans to install tsunami hazard and evacuation signs along the city's shoreline in 2027. SDOT owns the signs and controls the timeline, and for now, that timeline is loose.

While places along the downtown waterfront and Shilshole Bay in North Seattle are considered tsunami hazard zones, several zones are located in South Seattle: First Avenue South, between Yesler Way and South Spokane Street; Harbor Island; and West Marginal Way Southwest, close to the Duwamish Longhouse and Cultural Center. Factories and warehouses along the Duwamish Waterway are also at risk of tsunami inundation and high-tide events.

Tyisha Brown El, a community engagement specialist with the Seattle Office of Emergency Management (OEM), said SDOT staff recently went into a city warehouse and photographed the signs. They're the standard signs used in California and along Washington's coast: markers for entering and leaving a tsunami hazard zone, plus evacuation route signs with an arrow that will usually point, as Brown El put it, "up and out of the way."

Where the signs will go is still taking shape. SDOT shared a preliminary map of proposed sign locations with the Emerald, but the department stresses the map isn't final. The draft locations are based on tsunami inundation maps, which show where water could reach, Brown El said.

Tsunami Risks Hard to Predict

So why is Seattle getting tsunami signs now? Brown El, who joined OEM in July after working in the state's tsunami program, points to two forces: money and science.

While at the state, she walked evacuation routes in Westport and saw firsthand that signs were in short supply. The state received grant funding to buy more, and local jurisdictions could request them.

"When funding comes around, we try to take advantage of funding to get signs, because it's expensive," she said.

The other force is a growing understanding of the Seattle Fault, which cuts beneath the city itself.

"Some people think there is no tsunami risk in Puget Sound, when there is," Brown El said. "Not just from Cascadia, but from the Seattle Fault too."

Ian Miller, a coastal hazards specialist with Washington Sea Grant, said the science around these threats never sits still. Washington has "a very active community of geohazard researchers," he said, working both to model what a major event might look like and to find evidence of past ones written into the landscape.

That work matters because no one living has seen one here. "We haven't experienced one effectively in the historic period," Miller said.

Part of what makes Seattle's risk hard to picture is that a tsunami in an inland sea doesn't behave like one on the open coast, Miller said. Computer models show waves growing taller when they're squeezed into narrow passages, the same thing you can see playing with ripples in a bathtub. Waves also bounce off land, and the Sound's geography sends them ricocheting in complicated ways.

A Cascadia Subduction Zone earthquake off the coast could send a wave not only toward beach towns but down the Strait of Juan de Fuca and into the Sound. Miller said Bainbridge Island wouldn't shield Seattle. "Those models suggest that wave is going to propagate basically anywhere connected to the Pacific."

The good news: The wave loses height on its way in, and the Sound buys time. A town like La Push may have 15 to 20 minutes to evacuate after a Cascadia quake. For Puget Sound's urban communities, models suggest closer to 90 to 120 minutes.

With that much time and steep ground nearby, Miller said, "If we are prepared, no one should die. We may lose infrastructure." But he was quick to add that there are places where that isn't the case.

When to Head Toward High Ground

A Seattle Fault quake is a different story. Because the fault is local, there's far less time between the shaking and the displacement of water. In places like Alki or Harbor Island, Brown El acknowledged, some people may not be able to get out of the hazard zone at all.

"People will not have as much time as someone who's in Ballard, just because of geographical location," she said. "That's when your preparation and your planning ahead of time comes into play."

Seattle won't have tsunami sirens or vertical evacuation towers. For a local quake, Brown El said, the shaking is the warning. "That is the time for you to start going inland to high ground." For a tsunami from far away, alerts will come by phone, social media, and AlertSeattle.

The signs also won't lead to designated gathering spots like on the Oregon coast. Brown El said identifying safe zones would take scientists, funding, and staff the city doesn't have, and it carries legal risk.

So the signs point in a direction. Where you end up is up to you, "so you would need to do that research for your own home and yourself," Brown El said.

Even that research comes with a caveat. Tsunami inundation maps show how far water could reach, but Miller said they're neither a floor nor a ceiling. "Really somewhere in the middle."

The biggest wild card may be the tide. On Seattle's waterfront, the water level can swing 15 feet in a day. The state Department of Natural Resources, which does most of Washington's tsunami modeling, runs its scenarios at a standard water level that Miller believes reflects mean high water, roughly the average daily high tide. A wave that lands at a higher tide reaches farther.

He pointed to the tsunami generated by the 2025 Kamchatka earthquake, centered in far eastern Russia, which reached Washington during that year's Intertribal Canoe Journey, while canoe families were camped on beaches with their canoes pulled ashore. The largest wave arrived near low tide. "If it had coincided with the high tide, it would have been a lot more concerning," Miller said.

Rolling the Dice

Then there are Kelvin waves, enormous and slow-moving ocean waves tied to El Niño, Miller explained. The Pacific's trade winds push water west and hold it there. When El Niño relaxes those winds, the water sloshes back east in waves thousands of kilometers long. When they hit the Americas, the rotation of the Earth holds them against the coast as they travel north and south.

You can't see them from shore. They're only inches to a foot tall. But they can raise coastal water levels for weeks, and they tend to peak in winter, the same season as Puget Sound's highest tides and worst storms.

"Every winter we're playing a game with dice," Miller said. Each storm is a roll. A Kelvin wave "would just be another [die] that you're throwing in there."

The nightmare scenario of a tsunami arriving on top of a Kelvin wave, a high tide, and a storm surge is unlikely, Miller said, but not impossible. "We rely a lot on just hoping that those kind of long odds don't play out."

Most of Seattle's shoreline armoring wasn't designed for tsunamis. The real vulnerability, Miller said, comes from what we've chosen to build at the water's edge. "In Seattle, at least, there is a ton of very high-value stuff right down near the shoreline."

The Time to Plan? Now

For residents who want to know where they stand, Miller recommends a few free tools. Start with FEMA flood maps to see whether your home or workplace sits in a current flood zone. For the future, he points to the U.S. Geological Survey's CoSMoS maps, now available for all of King County, which let you pick different sea-level and storm scenarios and see where water is expected to go. Washington Sea Grant also offers an interactive tool, built from the 2018 statewide sea-level rise assessment Miller led, that gives local projections for places like Elliott Bay and accounts for whether the land there is rising or sinking.

And don't discount what you've seen with your own eyes, he said. The Dec. 27, 2022, coastal flood broke records across much of Puget Sound and led to the first emergency evacuation for coastal flooding in the Sound that Miller knows of.

Brown El urged people to plan for more than one scenario. OEM's community engagement team has just four people, she said, so the office is recruiting community safety ambassadors, bilingual and trilingual residents trained to bring preparedness information into communities that speak Vietnamese, Arabic, Swahili, and other languages. OEM is also partnering with Seattle Emergency Hubs, revamping its old neighborhood program as Ready Together, and reaching out to workplaces and the hospitality industry. She hopes to have a stronger ambassador team in place in 2027.

Once the signs are up, Brown El would like to see people actually walk the routes, maybe during future Great ShakeOut drills — the next one is Oct. 21, 2027 — or a 5K organized with Seattle Parks and Recreation and the Department of Neighborhoods. Those talks are informal for now, she said.

"Our goal is to get more people involved in a realistic standpoint," she said. And, Brown El stressed, be prepared and start with a plan.

"Having that plan, even if it's small, even if it's not the most robust," she said, "having something to start off with is better than nothing."

Disclosure: Alex Garland has a degree in emergency administration and disaster planning and is the owner of KnowDisasters.com, an emergency management consulting company.