Some modest turbulence has the kids a little nervous as the nice British family flies into Thailand for vacation, but after that, the worst problem anyone faces at their idyllic oceanfront resort is a bad sunburn.

Director Juan Antonio Bayona shows intense restraint in “The Impossible” as he sets the scene for this century’s most horrific natural disaster, the tsunami that, on Dec. 26, 2004, swept in from the Indian Ocean to wipe out 200,000 lives in Southeast Asia.

Children play on the beach and dive in the waves; vacationers sleep in late and stroll under the palm trees. The Bennett family – Henry, Maria, and their sons Lucas and the two littlest boys, Simon and Thomas – have an away-from-home happy Christmas and the next day splash gaily in the pool when suddenly – incredibly suddenly – everything feels wrong. People in harm’s way barely have time to notice before disaster overwhelms them.

The filmmaker’s re-creation of the great wave is stunning. It is felt in the air, then heard on the wind; the tops of trees start to topple like dominoes from the beach on inland until the unimaginable wall of water appears.

And then the people, the trees, the landscape are gone.

Naomi Watts as Maria resurfaces clinging to a tree trunk and screaming in terror. Lucas (Tom Holland) appears soon after, a bobbing, crying body in the churning sea. With wreckage swirling all around them, the two struggle to remain together, afloat and alive.

It is harrowing and powerful, and impressive filmmaking. And, at least the frame of the story is true. A family much like the Bennetts – a Spanish couple and their three sons – was vacationing in Thailand when the tsunami hit, and the film, with an English-speaking family in their place – is based on their experience.

After the roar and the rush of water, the bloodied and badly bruised Maria and Lucas struggle out of the debris into a nearly silent world. The elation of having found one another dissolves under the realization that the rest of their family is gone.

Telling the story of such astounding destruction and loss is full of pitfalls – characters can be drawn as too noble or too sappy, or be made to choose between freakish hysteria and superhuman stoicism. Bayona dodges those traps fairly well.

Survivors are stunned and suffering, some are in shock and some remain terrified, but they are there for one another, as are the people who are now tending to them – overtaxed medical personnel, locals from higher ground and officials, all trying to save those they can, reunite families, and identify the bodies.

These people are mostly background, though, for the experience of the Bennetts. As the severely injured Maria, Watts spends most of the film in a hospital bed, turning deeper shades of purple and swelling from a raging infection.

The spare, effective filmmaking suffers as the story moves on, with the addition of what feel like contrivances, and as the quiet moments that were so powerful earlier disappear under music reminiscent of “Gone With the Wind.”

Ewan McGregor keeps it real, though, as the battered and barefoot Henry, frantically searching for his family, and also trying to get word to those back home. When he finally does, on a borrowed phone, his mask of hope disintegrates. Overwhelmed by the disaster and the seering pain of each of the thousands upon thousands of losses, he collapses in tears.

It is a mixed-up movie, part docu-drama, horror film and feel-good triumph. You could blame the director for not showing enough of the magnitude of tragedy, and for focusing on the resorts’ European guests over the tens of thousands of Asians killed, and that criticism would be valid.

But, taking it for what it is, the retelling of one family’s experience, and with winning performances by Watts, McGregor, the youngest boys and especially by Holland, “The Impossible” has the power to sweep you away.

The Impossible

3 stars

Starring: Ewan McGregor, Naomi Watts, Tom Holland

Director: Juan Antonio Bayona

Running time: 114 minutes

Rating: PG-13 for intense realistic disaster sequences, including disturbing injury images and brief nudity.

The Lowdown: Based on the true story of a family caught in the deadly 2004 tsumani in Thailand.