Harry Potter is 13 now, an awkward age for anyone – even a boy wizard armed with magical powers.

But “Harry Potter and the Prisoner of Azkaban,” the third film in the series, couldn’t be more self-assured.

Alfonso Cuaron, best known for making the gritty coming-of-age film “Y Tu Mama Tambien,” has taken over directing duties and taken the tale in a darker direction.

Much of that comes from author J.K. Rowling’s source material itself – “Azkaban” is heavier thematically than its predecessors, as Harry learns more about how his parents died and begins to understand who he really is.

Visually, though, “Azkaban” isn’t as glossy or whimsical as the first two films, “Harry Potter and the Sorcerer’s Stone” and “Harry Potter and the Chamber of Secrets,” both of which Chris Columbus directed. Cuaron has completely reinvented the series with a bleakly beautiful style that resembles German expressionism, using cold shades of gray, a generous amount of black and off-kilter camera angles.

The skies are constantly cloudy over the Hogwarts School of Witchcraft and Wizardry, and even a game of Quidditch, the young wizards’ beloved sport, takes place in a driving rain storm.

It’s a daring move, one that makes “Azkaban” more stimulating for adults but may have resulted in a film that’s too scary for young kids.

The Dementors – hooded creatures who guard the Azkaban prison and suck the souls from their victims – are sent to Hogwarts to protect the students from escaped wizard Sirius Black, but that doesn’t make them any less ominous.

“Azkaban” has some wondrous moments, too. A scene in which Harry (Daniel Radcliffe) takes a ride on a hippogriff – a flying animal that’s half horse, half eagle – has a soaring, I’m-the-king-of-the-world energy about it, only without the bombastic Celine Dion music.

The supporting cast is more fabulous than ever. Besides the returning actors – including Alan Rickman as the snippy Professor Snape and Robbie Coltrane as the lovable giant Hagrid – there are some wonderful additions.

David Thewlis plays the supportive Defense Against the Dark Arts teacher who helps Harry face his fears, and Emma Thompson is a scene stealer as a hippie-chick divination professor, a showy role that’s a great contrast with the prim parts for which she’s best known. As the mysterious, misunderstood Sirius Black, Gary Oldman infuses his character with great heart and sympathy.

(Michael Gambon takes over seamlessly as Hogwarts headmaster Albus Dumbledore, the role Richard Harris played until his death in 2002.)

Most importantly, Radcliffe and the young actors who co-star as Harry’s pals are more confident than ever. Radcliffe, who was a likable if slightly goofy kid in the first two movies, has grown into a charismatic (and cute) 14-year-old.

Emma Watson, as Harry’s bossy buddy Hermione, has developed into a strong, beautiful young woman. And as Harry’s best friend, Ron, Rupert Grint shows an improving sense of humor and timing.

Rated: PG for frightening moments, creature violence and mild language. Running time: 141 minutes. Rating: 3 1/2 out of 4 stars.