There were perfect waves the day the planes hit the buildings. They were clean, well-spaced, head high at least and maybe higher. They rolled into Squibnocket and Aquinnah under a cloudless sky across the glassy sea from a hurricane named Erin, the eye of which passed a few hundred miles off the coast of New York and New England on Sept. 11, 2001.

I wasn’t much of a surfer. But I was still young enough or game enough in those days to subject myself to repeated trips through the wash cycle of failure on wave after wave for chance at a few sublime seconds of sliding down the face of that pent-up energy that the world was sending our way. There were maybe a dozen of us who got out there early enough to be sitting in the lineup before any of the news began to arrive in bits and pieces from latecomers to the surf.

“A private plane accidentally hit one building . . .” “A jetliner hit one building . . .” “Another jet hit the other building . . .” “The Pentagon . . .”

As the news filtered out and the sun climbed and the day became even more impossibly beautiful, the usual friendly banter that can go on among surfers dwindled. It’s an odd place for conversation anyway, because one moment you are at the bottom of a trough looking up at your neighbor and the next you are atop the swell peering down. And if you are talking to someone whose lucky moment comes in the middle of a sentence, they are gone, either holding their breath in the ringer or giddily gliding away along the shore with their back to you. Eventually no one talked at all. We all knew as much as we wanted to know, and no one wanted to go home and find out more. It couldn’t be good.

Everyone who was alive then, no matter where they were, no doubt remembers the way the story trickled in and the horror mounted. Everyone remembers the sense of powerlessness in the face of something huge and unknown approaching. A rogue wave. A tsunami.

Everyone probably also remembers engaging in the personal calculus of disaster, the running through the mind of who one knows who might have been on a plane from Boston to Los Angeles, or at the Pentagon, or at the World Trade Center. I know I did, as I sat out there rising and falling on the swells.

I focused my thoughts on the towers, as I was still relatively fresh to year-round living on the Vineyard and I had lived for many years in downtown Manhattan, not all that far from the scene of the devastation. Nina and I fell in love there. Invented our life together there. Most of our best friends still lived in “the city,” as we called it. In the bright sunshine I went through everyone I could think of, and with relief determined that I knew no one likely to be down in the financial district.

But I had badly miscalculated. David Rivers, my one friend who had grown up on the Vineyard and probably my best friend at that time, was in a rogue breakfast meeting at Windows on the World. Enough said. I see his son now and then, all grown up and strong, who was too young to remember much. And when I go to New York I see his wife, who has doubtless not forgotten a thing, but who is as strong a person as I know. I see David’s own smiling face beside the two of theirs in a framed photo on my piano when I sit down to try and play, which I do about as well as I surf.

Grief is said to come in waves. As does music and light. And violence. Even the tides, I have read, are best understood as a globe-spanning wave system with two peaks, two troughs, and a wavelength of half the world. There are too many metaphorical threads to explore. Or, at least, I am not the one to untangle them.

What I do know is that the danger posed by any given wave depends less on the thing itself than on where you find yourself in relation to it. There is a photograph taken from space at 10:39 on the morning on Sept. 11, 2001 that shows Hurricane Erin off the coast. The great round tempest looks to be five hundred miles across, its outermost bands barely grazing Sconset at the eastern tip of Nantucket. But it’s cloudless over the Vineyard, cloudless over Squibnocket. And cloudless, too, over Long Island and New York city. Except for a single visible plume of smoke from the bottom of Manhattan.