The event could become a disaster as people struggle with the difficult conditions in Nevada without proper preparation, they have warned.
Those arriving to the tiny towns of Rachel and Hiko, near Area 51, are doing so because of a Facebook event that was one of the site's most popular ever, before it was shut down. The page, which encouraged people to "see them aliens" and suggested that enough people raid the base then they couldn't be stopped, is bringing an unknown number of people to Nevada to take part in the event.
Local officials have already signed emergency declarations in response to the event, and local residents warned people not to come. But the event is still likely to prove popular, leading people to take precautions against whatever might happen.
"We are preparing for the worst," said Joerg Arnu, a Rachel resident who could see from his home a makeshift stage and cluster of portable toilets in a dusty area recently scraped of brush surrounding West's little motel and cafe.
Arnu said he installed outdoor floodlights, fencing and "No Trespassing" signs on his 30-acre property. He's also organised a radio-equipped night watch of neighbours, fearing there won't be enough water, food, trash bins or toilets for visitors.
"Those that know what to expect camping in the desert are going to have a good time," Arnu said. "Those who are looking for a big party are going to be disappointed."
He predicts people showing up in the desert in shorts and flip-flops.
"That doesn't protect you against critters, snakes and scorpions," Arnu said. "It will get cold at night. They're not going to find what they're looking for, and they are going to get angry."
Officials expect cellular service to be overwhelmed. The nearest gas station is 45 miles away. Campers could encounter overnight temperatures as low as 5C.
"We really didn't ask for this," said Varlin Higbee, a Lincoln County commissioner who voted to allocate $250,000 in scarce funds to handle anticipated crowds.
"We have planned and staged enough to handle 30,000 to 40,000 people," Higbee said. "We don't know how many will come for sure."
Though the creator of the Facebook event later called it a hoax, the overwhelming response sent local, state and military officials scrambling. Promoters began scouting sites. A beer company produced alien-themed cans. A Nevada brothel offered discounts to "E.T. enthusiasts."
The Federal Aviation Administration closed nearby air space this week.
The U.S. Air Force has issued stern warnings for people not to approach the gates of the Nevada Test and Training Range, where Area 51 is located.
Area 51 tested aircraft ranging from the U-2 in the 1950s to the B-2 stealth bomber in the 1980s. The government spent decades refusing to acknowledge the site even existed, before releasing documents confirming it in 2013. Its secrecy still fuels speculation that it's where the government studies aliens.
County lawmakers in Nye County, home to a conspicuously green establishment called the Area 51 Alien Center, are discouraging Earthlings from trying to find extraterrestrials there.
"We're taking precautions and checking the back roads," Sheriff Sharon Wehrly said.
Her deputies last week arrested two Dutch tourists attracted by "Storm Area 51." The men pleaded guilty to trespassing at a secure U.S. site nowhere near Area 51 and promised to pay thousands in fines.
Arnu said the military added razor wire to barbed cattle fencing on the Area 51 boundary near his home, installed more cameras and battery-powered lighting, and erected an imposing spike barrier just inside a gate. He noted a new sign telling trespassers they'll be arrested and fined $1,000.
Hundreds of law enforcement officers and medics will be on hand, along with the Nevada National Guard.
Additional reporting by Associated Press