TIJUANA, Mexico — When the Central American caravan finally crosses onto U.S. soil — past the fresh coils of barbed wire, through the chain-link door — its people will begin a closely monitored existence in U.S. custody, with showers every two days and guard checks every 15 minutes.

They will live at the San Ysidro port of entry in one of 31 holding rooms with painted cinder-block walls, the largest of which holds space for 25 people, sleeping under Mylar blankets on rubber mats, watched by video surveillance. They will have two hot meals a day, a cold lunch and possibly cereal before bed.

What the experience won’t be, for the several thousand migrants who are now pooling up in Tijuana, is fast.

“We have a process in place,” said Sidney Aki, the San Ysidro port director for U.S. Customs and Border Protection. “Please be patient.”

Defense Secretary Jim Mattis and Homeland Security Secretary Kirstjen Nielsen visited the U.S.-Mexico border Nov.14. (Reuters)

After more than a month and some 3,000 miles, the caravan has reached the end of its road. What had been a plodding slog through southern Mexico rapidly accelerated in the past week, as many migrants rode in buses , provided by local governments, along the route from Mexico City north to the border. More than 2,000 people have arrived in Tijuana this week, with another 7,000 not far behind, according to Mexican authorities. That doesn’t include the roughly 3,000 migrants who were already in Tijuana seeking legal entry into the United States.

For many in the caravan, the next step is to apply for asylum at the San Ysidro border crossing, and what that means is waiting.

During one day in May 2016, U.S. border authorities allowed more than 1,000 Haitian asylum seekers into the port of entry. To handle the influx, they converted staff offices into holding cells; employee showers became migrant showers. Overtime pay surged; they were short on food and supplies.

“The operation got overwhelmed,” said Mariza Marin, a CBP watch commander.

The lesson for Aki and his subordinates: Never exceed capacity. They say they can process 90 to 100 migrants per day and have a total holding space for about 300 people. Francisco Gomez, a top official in Baja California, the Mexican state which includes Tijuana, estimated that the caravan would be there four months or more.

At this newly renovated port of entry — the busiest on the border, Aki said, with some 100,000 legal travelers crossing into the United States each day — asylum seekers will stay in detention for up to 72 hours before being transferred by Immigration and Customs Enforcement officials to other facilities for children, adults or families. Waiting for ICE is a major bottleneck, Aki said.

“We’re taking the blame for everything,” Aki said. But until ICE moves migrants out, “we can’t do anything.”

ICE did not immediately respond to a request for comment.

In the port of entry, migrants will be fingerprinted and checked for criminal records or deportation histories. They will be searched for weapons and examined for ailments such as head lice, chickenpox and scabies.

CBP officials take a preliminary statement from migrants; later, asylum officers will interview them to see if they have a “credible fear” of returning to their home countries. If so, they will enter an immigration court process in which a judge will ultimately decide. The vast majority of those who apply for asylum do not receive it.

Those not applying for asylum will probably be deported.

“If you’re not claiming fear, then we are expeditiously removing you,” Aki said.

The caravan also includes single men who say they will attempt to cross the border illegally and others who plan to stay in Mexico.

“It’s impossible to get asylum, so I won’t do that, but I want to do things legally,” said Sarah Ilatina, 28, of Tegucigalpa, Honduras. “I hope [President] Trump opens his heart to us.”

By the time she arrived in Tijuana on Thursday morning, carrying a plastic bag with toilet paper and water, it had been 24 hours since her last meal, she said. She joined the caravan last month because she had not been able to find work in Honduras despite her accounting degree. She has family in Miami and wants to join them.

“I’m not coming to hurt anyone or take anything from anyone,” she said. “I don’t want to throw myself over the walls.”

Trump has likened the caravan to an “invasion” and called on the U.S. military to fortify the border. U.S. Marines have strung up barbed wire between lanes of traffic at the port of entry in case migrants try to push past guards. On Wednesday, as some migrants convened on the beach in an upscale part of town, a group of residents shouted at them to go elsewhere and threatened violence. Police formed a barricade to separate the sides after a scuffle broke out. While U.S. authorities say they are prepared for anything, they expect a slow and orderly process. And so do migrants.

“Putting troops up at the border like we are going to do something?” said Alejandro Gomez, 39, a migrant from Choloma, Honduras. “We aren’t. That’s all a circus.”

For now, migrants are camped out at a sports complex in Tijuana and scattered among other shelters.

Derien Antonio Carbajal Alvarado, 21, pitched a tent and set up cots for his pregnant girlfriend and her three daughters, ages 5, 6 and 7. He said he had been shot in the arm by gang members and went to the police after receiving more threatening texts and Facebook messages. Those messages and the police report are the evidence he hopes will sway an immigration judge, but he doesn’t know for sure how it all works.

“I don’t know what Trump is saying; we’ve been walking, and I’m not a well-informed guy,” he said. “I’m just a taxi driver from San Pedro Sula, Honduras, and I want a better life for my daughter that is on the way, and my stepdaughters.”

He has family in Dallas and hopes to somehow make it there. He’s ready to drive a taxi.

“Or whatever there is available,” he said.