'San Andreas' opening beats expectations, but...

A scene from the film San Andreas.
Source: Warner Bros. Pictures | YouTube

The first weekend for "San Andreas" may mark the end of the perfect run of movie predictions made by a model by Adobe Digital Index, which has used social data to forecast 24 hits and flops without error over the past two years.

The movie beat analysts' expectations by about $13 million, pulling in over $53 million—almost half of its production cost of $110 million. Does that mean that the summer movie prediction model is broken? Not necessarily.

For one thing, just because a movie does well during its opening weekend doesn't mean it will make enough in the U.S. to pay for production costs. CNBC looked at every movie that made $50 million to $60 million over the last decade, and found that more than 1 in 4 were still not domestically profitable (Adobe's model doesn't count foreign social media or earnings).

Based on the 36 movies in the dataset above, the first weekend accounts for an average of about 35 percent of a movie's total domestic box office earnings. At that rate, "San Andreas" can expect to make about $42 million more than its production costs.

But Warner Bros. executives must surely be hoping that "San Andreas" doesn't follow another of the studio's movie, the 2009 domestic flop "Watchmen." It sold a promising $55 million in tickets on its first weekend but only managed to eke out another $52 million more in the U.S. after that, falling short of its production budget by $30 million. At that rate, "San Andreas" would fall short by about $6 million.

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In the end, it seems likely—but not guaranteed—that "San Andreas" will be one of the winners. The movie has a surprisingly low budget for a disaster movie, making it easier for it to sneak into profitability. In comparison, 2009's "2012" cost $200 million to make, and all of the flops in the chart above cost at least $137 million. No major action movies are being released this week, giving the movie a further edge.

Why did the model fail?

Leading up to its release, "San Andreas" was trending below even the level of previous unprofitable movies like last year's "Hercules," which also featured Dwayne "The Rock" Johnson as the leading man. Despite Johnson's massive army of online followers, Adobe Digital Index analysts found that the movie was barely stirring up any interest online.

"We picked on The Rock for his fandom not being activated," said Tamara Gaffney, principal analyst at Adobe Digital Index. "Just when we said that, the next day he activated his fan base."

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Johnson launched a social media promotion campaign on Facebook, Instagram and Twitter at the last minute, boosting the film's exposure in the days before release, said Adobe Digital Index Manager Joe Martin, who created the movie model. Social sentiment for the movie also shifted, becoming more positive going into the weekend.

"It looks like we're going to be wrong for the first time," said Martin. "But look at how fast you can activate a fan base and change the fortunes of what could have been a flop."

Even if "San Andreas" earns back its full $110 million in the U.S., as Martin suspects it will, the outlier in the model will be used to make its predictions more accurate going forward, he said. The next predictions will be adjusted for the amount of marketing spending and social outreach that takes place in the week before release, which seem to fill seats even if earlier marketing efforts didn't bring much response on social media.

Warner Bros. declined to comment on the movie's prospects.

Disclosure: CNBC's sister company Universal produced "Snow White and the Huntsman," "The Incredible Hulk," "Ted," "Despicable Me," "Wanted," and "King Kong."