The National Weather Service on Sunday warned that Harvey “is unprecedented” and that its impacts “are unknown” and “beyond anything experienced.”

This event is unprecedented & all impacts are unknown & beyond anything experienced. Follow orders from officials to ensure safety. #Harvey pic.twitter.com/IjpWLey1h8 — NWS (@NWS) August 27, 2017

The National Weather Service issued the warning two days after Harvey made landfall Friday night, amid ongoing rescue attempts, severe flooding and damage from the hurricane.

Asked on CNN’s “State of the Union” about long-term recovery efforts for the storm, Federal Emergency Management Agency chief Brock Long said the agency will “be there for years.”

“This disaster will be a landmark,” Long said. “We’re setting up and gearing up for the next couple of years.”

He said Harvey is “nothing like Katrina,” the 2005 hurricane that devastated New Orleans.

“This is a storm that the United States has not seen yet,” Long said. “It started with a category 4 with storm surge right off the coast, and now it’s bleeding into a multiple day inland, inland threat from torrential rainfall.”