As the waves of an extreme high tide pounded the sliver of sand at Queens Beach, Waikiki, at about 5 p.m. Tuesday, crashing against the sea wall and sending up overhead plumes of spray, Honolulu Ocean Safety lifeguard Cole McPherson, sitting in Tower 2-F on the beach, suddenly felt something strange.

“The tower was shifting,” said McPherson. “It was scary.”

He called his supervisors, who ordered him to abandon the 10-foot-high tower, mounted on a concrete cylinder and slab base, which posed a hazard to the lifeguards and the public.

“The tower was leaning forwards at about a 15-degree angle and looked about to fall over on its edge,” said Ocean Safety Chief John Titchen. “We think what happened was the concrete slab was undermined by wave action and sea level rise.”

This “manini” incident underscored the enormous and urgent threat of sea level rise, which Ocean Safety was actively considering and assessing among other hazard risks, Titchen said Friday as he sat on a bench in Queens Beach Park overlooking the site, and pointed out a layer of sand that had been carried onto the park’s walkway by the waves.

Tower 2-F was gone, having been removed Wednesday morning by the city Department of Parks and Recreation’s divisions of Urban Forestry and Maintenance Supply Services, leaving behind only the thick concrete cylinder on its slab, resting on the wet sand.

“It’s more stable now with the tower removed,” Titchen said, adding that the concrete remainders would be taken away late next week, as city staff were currently busy preparing for Hurricane Douglas’ predicted landfall Sunday.

Nearby, with binoculars raised, McPherson stood at the edge of the sea wall surveying the ocean from the temporary shelter of a red-and-gold Ocean Safety canopy tent, adjacent to where, now fenced and coned off, a concrete ramp that had descended from the sea wall to the beach also had been been destroyed by the Tuesday incident.

“Tower 2-Foxtrot was the first of our 41 towers we staff around the island to be so significantly affected by erosion as to be in danger of falling down,” said Titchen, who supervises the 250 Ocean Safety officers who also conduct mobile surveillance of Oahu’s beaches and nearshore waters from personal watercraft, UTVs and trucks.

But “the beach under that tower was eroding when I sat in it 20 years ago,” the former city lifeguard said, adding that the new culprit was sea level rise, which produces the ”king” high tides of the sort that struck Tuesday.

“On Tuesday at 5 p.m., an extreme high tide was just reaching its peak height of 2.4 feet, and we had anticipated it could get to more than 3 feet with an additional 6-8 inches of water due to sea level rise,” he said.

The tower’s vulnerability, Titchen added, was exacerbated by the sea wall’s hardening of the shoreline, which increases beach erosion. Unlike most other towers, it had had to be placed on a heavy concrete base rather than atop a stainless-steel frame with legs driven deep into the sand.

Because there was no space left higher up the beach, Ocean Safety was determining where to place either the same, repaired tower or a new one. The one- and two-person towers are made in San Clemente, Calif., and a single one costs about $70,000.

“We’ll have to assess sea level rise, high tide and the effects of hurricanes before we place the tower again,” Titchen said.

However, despite sea level rise and the need to increase and improve mobile ocean safety units to patrol unguarded stretches of coastline, especially around events such as hurricanes and tropical storms, he believed there always would be a need for fixed lifeguard towers.

“The towers were placed where they need to be, based on (numbers of) drownings and other incidents, where there are higher risks from waves, reef, currents and crowds,” Titchen said. “There’s a continual increase in ocean activity in Oahu waters.”

Towers “provide a base for our staff and are reassuring to the public,” he added.

Noting that Ocean Safety had received capital improvement funding from the city even in the midst of this pandemic, “I think we’re always going to have towers,” Titchen said as he watched a flock of surf school students paddling out to the shallow, reefy break at Public Baths, directly in front of where Tower 2-F once stood.