In the space of two seconds she will perform somersaults and twists before slamming into the water at high speed.
As the world's leading female cliff diver, the American looks the model of calm as she gears up to jump. So does she ever get scared?
"I try to keep it simple -- when I overthink things, that's when I start getting nervous and I have to remember I've done these dives hundreds of times.
"I do a lot of visualization, breaths, prayer, get to the end of the platform, and it's 1, 2, 3, go."
Simpson and her fellow female cliff divers jump from 20 meters (65 feet) -- twice the height of the highest Olympic diving platform -- and entering the water feet first.
"People have gone head first from that high, but it's really hard on the shoulders and definitely you don't want to just be doing that all of the time," Simpson explains.
"Ten-meter divers can take pretty bad hits but for the most part can walk away. When you're up on 20 meters or higher (men dive from 27 meters) there's less room for error.
"During the dive, we can get up to about 55 miles per hour, and depending on entry, it can feel like you're landing on concrete.
"It's such a hard impact. You need to make sure your body is ready for it."
That means plenty of work in the gym, but it's the mental side that requires the most attention.
"Obviously, you need some physical capability, good body awareness, tight core, and things like that. But those can be learned.
"I feel like divers, especially if you're wanting to be a high diver, you need to be able to keep yourself mentally calm. When you're getting amped up, that's when you can really mess up."
But when everything clicks, as it does frequently for the 27-year-old, the rewards are incredible.
"It's like no other feeling ... you just let the body take over," she says.
"That feeling of weightlessness, and then the rush -- and when you have a great entry, it's even better."
Born in San Antonio, Texas in 1988, Simpson was perhaps always destined to follow an acrobatic path in life.
"My parents owned a gymnastics school for about 20 years, so I was practically born in the gym," she explains.
"My mom went into labor in the gymnastics school, so ever since I could walk, I've been flipping, climbing on things."
She joined a local boys' diving team -- "I was a bit of a tomboy," she says -- and soon earned the nickname "Rocco" thanks to "rocking" dives, she explains.
As an adult she has worked as a professional acrobat and first tried high diving on stage, as part of the cast of "The House of Dancing Water" a Chinese theatrical production combining elements of dance, gymnastics and diving.
"I did that for about two and a half years, and then in 2014 Red Bull announced they wanted women for the cliff diving series
. I sent in a video of myself, and they accepted me."
Simpson is the undisputed star of the competition, winning all three events last year to become its first female champion.
"To win the series last year was an incredible feeling. I had come in just hoping to showcase what I'd been doing in the (stage) shows before," she says.
"I wasn't coming in expecting to win. Obviously, I was hopeful and I knew I had the highest degree of difficulty -- three forward somersaults in the pike position followed by one and a half twists. I wanted to show that I could execute that well."
She has carried that good form into the 2015 season, claiming gold in the high diving competition at August's FINA World Championships in Russia and then retaining her Red Bull Cliff Diving
title by winning the final event of the women's series in Polignano a Mare, Italy in front of 55,000 fans.
She's hopeful that the sport will eventually find its way onto the Olympic program, fulfilling a dream that she thought would never come true.
"To be in the Olympics would be another highlight in my life," Simpson says.
"I was an okay gymnast, but I gave up the dream of the Olympics a long time ago. To have it even just be whispered for the future -- just to have it in my thoughts is really cool."
Ultimately though, her aims are more altruistic.
"My end goal is for younger girls to see this and know that women can do incredible things and to spread the word," says Simpson.
"(We had) 10 women (compete) this year. Last time, we had eight. So I really would love to see this become super popular and just get the younger generations involved."