For a film that is alternately emotional, “The Impossible” grabs your attention with a scene worthy of a high-end disaster movie: an incredible depiction of a tsunami. Knowing that it’s coming, as many people will from the previews and advertisements, won’t lessen the impact of this tour de force, which is frighteningly believable in every detail. By that I mean the Indian Ocean tsunami that wreaked havoc on Thailand in 2004. The aftermath of that disaster focuses on a family of five, British exec Henry Bennett (Ewan McGregor) and his doctor wife, Maria (Naomi Watts), who had brought their three sons there for a Christmas vacation. I don’t see the need to reveal more. The story is thoughtful and obviously sincere, which is why I was absorbed at every turn, even though I knew where it was heading. Director J.A. Bayona (“The Orphanage”) tells the story with the sure-handedness we’ve come to expect; He based his movie on the experiences of a Spanish family who really survived the deadly tsunami, which makes it even more credible. The film is also an impressive visual achievement, made more affecting by the sincerity the actors bring to their characters. The intensity and emotional power Watts brings to her role is simply outstanding. And McGregor matches her in an equally terrific performance. But the real surprise here is young Tom Holland (in his film debut), who gives this unforgettable film its grieving heart. If you’re willing to take a journey that is both devastating and rewarding, I’d say “The Impossible” is the movie for you.