The heat and humidity could be daunting for fans who come to Memphis from all over the world and line up for hours before the procession — which winds up Graceland's long, sloping driveway, past Presley's grave in a small garden beside the house.
"If you're back at the backside of that crowd, you're like five hours away from going up the hill," said Jack Soden, chief executive of Elvis Presley Enterprises, the company that manages Graceland and its sprawling tourist complex.
The vigil is the most popular and solemn anniversary event in a weeklong string of concerts, dances, movie screenings and other festivities put on by Graceland.
A particularly large crowd is expected Wednesday amid a brutal heat wave, with temperatures predicted to hit 104 degrees. The heat index, taking into account the effects of humidity, is predicted to be as high as 111.
"I don't think we've ever seen weather this hot before," Graceland tourist Hazel Dixon told Early Show meteorologist Dave Price.
"We're gonna dress light, drink lots of water and wear a hat, do everything we can to stay cool," Christine Cline told Price.
The famous white-columned house, which sits in a run-down Memphis neighborhood, draws almost 600,000 visitors a year. Up to 40,000 people file through it during the death anniversary week.
When Elvis died on Aug. 16, 1977, at 42 from heart disease worsened by drug abuse, his finances were in sad shape. Led by ex-wife Priscilla Presley, the estate formed Elvis Presley Enterprises, opened Graceland to the public and solidified the legal rights to make money on Elvis' name and image.
Last year, Graceland took in $27 million in revenue, and the overall Elvis business brings in more than $40 million a year. That made him the second-highest grossing dead celebrity in 2006, behind only Nirvana's Kurt Cobain, according to Forbes.
For the vigil, fans gather in the four-lane street in front of Graceland for an opening ceremony. As the procession starts, they light candles from torches lit by an eternal flame at the grave.
Many of the more experienced Graceland visitors have learned to leave after the opening ceremony and then return to join the procession hours later when the line has thinned.