In tennis, weather becomes another opponent. From switching sides to swapping tennis balls to closing the roof entirely, here's how the U.S. Open adapts when Mother Nature starts influencing the match.

Why players switch sides

At the U.S. Open, players can experience two very different environments on the same court. Sun glare can make a serve harder to see from one end, while stadium shadows force players to adjust their sightlines in the middle of a match.

(FORECAST: What to expect at this year's U.S. Open)

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Wind adds another layer of difficulty. A player hitting into the wind may see the ball slow down or fall short, while the player hitting with the wind can get extra carry on a shot. Crosswinds can also push the ball off its trajectory.

So switching sides guarantees neither player gets stuck with the bad side for too long. Changing sides helps ensure both competitors eventually face the same conditions (sun, shadows, wind) such that neither player suffers an unfair visual disadvantage while serving or tracking a shot.

Why the balls get changed every few games 

New York's late-summer humidity becomes part of the ball's environment too. As humidity rises, the air becomes less dense. Repeated strikes to the ball and contact with the hard court gradually fluffs up the ball's felt.

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That fuzz matters. A rougher, fluffier surface creates more aerodynamic drag as it traps moisture and air, which can slow the ball and change how it travels through the air.

Fresh tennis balls are smoother and more buoyant against the racket.

The U.S. Open adheres to a strict ball-change schedule. Fresh pressurized balls are introduced after the first seven games and then every nine games after that, with the warm-up counting as the first two games.

Why closing the roof changes everything

At Arthur Ashe Stadium and Louis Armstrong Stadium, closing the retractable roof can turn the U.S. Open into a very different kind of match. With wind largely removed as well as temperature and humidity more controlled, players get a cleaner and more predictable environment. The ball can travel more consistently, and bounces are less affected by the weather.

With fewer gusts to disrupt serves and through shots off line, players can take the ball earlier, more aggressively, and settle into a rhythm faster. The controlled space also reduces the ball's drag from moisture.

(MORE: ATP's new heat rule could reshape US Open)

But there's a caveat. Once the roof closes, crowd noise, racket strikes and even the sound of the ball can echo through the stadium. This creates a disruptive sensory environment for players.

What starts as a weather decision can end up impacting the speed, sound and rhythm of the entire match.

Each Grand Slam has its own weather challenge. Roland-Garros plays on clay, where rain and wind quickly change the surface, while Wimbledon's grass is sensitive to wet conditions. The Australian Open has become known for battling Melbourne's extreme heat, with retractable roofs. At the U.S. Open, New York can throw a little bit of everything at the player — heat, humidity, wind, and summer storms.

(WATCH: How heat makes Wimbledon's grass courts a tougher match)

The bottom line: Tennis has always been a sport that has to adapt to weather. But at the U.S. Open, everything from switching sides and swapping balls to closing the roof gives players and fans more ways to adjust when conditions change.

Faiza Mohammed is a meteorologist intern at weather.com. She studied geography and worked with the Weather Dawgs team at the University of Georgia. She also received her master's in Earth and Atmospheric Sciences from the Georgia Institute of Technology.