Can we get a "tragic chorus" up in here? We're not sure if that's what Heaney meant when he wrote that line, but we do know that there isn't one distinct speaker in this poem. The first word of the poem is "we," which tips us off that it's a community of people who are speaking in this poem.
Those people are the people who live on the island in the squat, sturdy homes. They appear to live a relatively isolated existence (well, they are on an island, so that shouldn't seem too surprising, but this is even more isolated, with a seemingly sparse population). The "we" in the poem talks about wanting "company" more than once, which gives us an indication that they might be a bit lonely, at least when the storms roll in. But, all in all, they seem like pretty sturdy folks—"[They] are prepared, [they] build their houses squat"—and regardless of how terrifying the storm may be, they're not about to pick up and leave. Finally, "we" here is a subtle invitation to us readers to consider ourselves right along with these islanders. After all, hasn't every single one of us run headfirst into Mother's Nature's power at some point?
Finally, among the "we" is a distinct "I" that pops up without warning in line 7 ("you know what I mean") to speak on behalf of the island crew. We can't say for certain who this spokesperson is, but we think it's safe to say it's one of the islanders—someone who knows firsthand what the storm on the island is like. In the way that any poet speaks up for the experience of other folks more generally, this "I" pipes up on behalf of the islanders. Unfortunately, he (if it is a he) has some bad news for us: we're all alone, and pretty powerless to stop the onslaught of the natural world.