When Hurricane Maria — the strongest hurricane to hit Puerto Rico in 89 years — descended on the Caribbean island on Sept. 20 with 30 inches of rain and 155 mph winds, the storm killed 16 people and left hundreds of thousands more without necessities like food, water, or medical care.

Since then, recently appointed FEMA administrator Brock Long characterized the ongoing humanitarian crisis there as “the most logistically challenging event the United States has seen” — although he caught some flack for the comment.

“We have been moving and pushing as fast as the situation allows,” Long added in a statement on Sunday. President Trump will visit the devastated Caribbean island on Tuesday.

Maria struck just weeks after Hurricane Irma, the strongest storm to ever come out of the Atlantic, swept across Puerto Rico and knocked out power for more than one million of the island’s residents.

Even though all of Puerto Rico’s airports and most of its ports are up and running, damage to the island’s roads has hampered relief to inland areas. Towns as close as 45 minutes outside of San Juan reported, as of Saturday, that no federal rescue efforts had reached them.

Here’s what Puerto Ricans are up against:

Roughly 8,800 refugees are now living in shelters across the island, Puerto Rican Gov. Ricardo Rosselló said Sunday. The government plans to house them across 139 shelters.

Gov. Rosselló has set also up 11 disaster relief staging points with enough coverage to service all 78 municipalities.

Heavy rains from Maria opened a crack multiple feet long in Puerto Rico’s Guajataca Dam, prompting the government to call for 70,000 people living nearby to evacuate, and residents are still under a flash flood watch from the National Weather Service.

Even those who still have homes face dire energy problems: 95 percent of the island remained without power as of Saturday, according to the Pentagon.

Key areas like hospitals and San Juan’s airport and ports have power, but officials warn it’ll take months before electricity is fully restored.

Gov. Rosselló and the mayor of San Juan have suggested restoring full power to the island could take up to six months, and the CEO of the Puerto Rico Electric Power Authority said it would be two or three months before even 50 percent of electricity was restored.

The company has 4,000 people working to restore electricity — with an additional 1,000 from private U.S. companies, according to Reuters.

The U.S. Army Corps of Engineers had delivered over 300 FEMA and Defense Logistics Agency generators to the island as of Sunday, with more arriving in the coming days.

Electric car maker Tesla also plans to send hundreds of solar electricity storage devices to help the island cope with outages.

Read more: Photos show insane lines for water, gas, and cash in Puerto Rico

In addition to the electrical grid, the island’s water systems also weathered massive blows. Only 45 percent of people had access to drinking water as of Saturday, according to the Pentagon. In response, FEMA has delivered two million liters of water.

Residents have taken to collecting rainwater in any containers they can, which scientists warn creates the perfect breeding ground for disease-carrying mosquitoes, which could soon overrun the island.

While FEMA reported that 851 of the island’s 1100 gas stations were open, the agency’s administrator Brock Long later said that only 765 had gas. In addition, long lines persist. One resident told VICE News that he had waited 20 hours for just 20 gallons of gas.

The Department of Defense estimates its relief efforts will bring a total of one million barrels of diesel and half-a-million barrels of gasoline in the coming days, alongside a potential 15,000 gallons of propane.

As of Sunday, FEMA had assessed all 69 of Puerto Rico’s hospitals, only one is fully operational. Fifty-nine are partially operational, with capacity for current patients or to receive patients.

The U.S. Department of Health and Human Services has opened seven temporary medical centers while hospitals are being repaired. A Navy hospital ship, the 1,000-bed USNS Comfort, is also due to the island Oct. 3 or 4. Some have noted it could’ve been deployed sooner.

As Puerto Rico struggles to reactivate its medical infrastructure, long lines for medicine have emerged, and scientists warn of a wave of post-disaster illnesses that could strike the island in its weakened state.

Read more: U.S. schools are preparing for Puerto Rican kids fleeing Maria

Sixty-five percent of grocery stores were open as of Saturday, according to the Puerto Rican government.

FEMA had delivered a million meals to the island, as of Saturday.

Almost 89 percent of sites in Puerto Rico were without cell service, the Federal Communications Commission reported as of Sunday. In some areas, the problem is even worse: 27 of the 78 counties on the island have zero service whatsoever.

All told, just 36 percent of Puerto Ricans have cell service, according to Gov. Rosselló on Sunday. That’s left people on and off the island scrambling to get in touch with friends and family members and often crowding in tiny spots that still have reception.

Over 12,600 federal staff representing 36 departments and agencies are on the island right now, according to FEMA. Major contingents include over 800 FEMA staffers and plans of 6,400 Department of Defense personnel.