Washington (CNN) President Donald Trump issued a strong warning to those in the path of Hurricane Florence , which is on track to hit the East Coast as a major storm later this week.

"The Storms in the Atlantic are very dangerous. We encourage anyone in the path of these storms to prepare themselves and to heed the warnings of State and Local officials. The Federal Government is closely monitoring and ready to assist. We are with you!" he tweeted Monday afternoon, shortly after South Carolina Gov. Henry McMaster ordered the mandatory evacuation of the state's coastline beginning at noon Tuesday.

Posting a video of the intensifying storm, Trump added, "To the incredible citizens of North Carolina, South Carolina and the entire East Coast - the storm looks very bad! Please take all necessary precautions. We have already began mobilizing our assets to respond accordingly, and we are here for you!"

To the incredible citizens of North Carolina, South Carolina and the entire East Coast - the storm looks very bad! Please take all necessary precautions. We have already began mobilizing our assets to respond accordingly, and we are here for you! pic.twitter.com/g74cyD6b6K

Trump received a Monday afternoon briefing from Homeland Security Secretary Kirstjen Nielsen and Federal Emergency Management Agency Administrator Brock Long via phone. He posted photos from the briefing that showed chief of staff John Kelly and Vice President Mike Pence seated by his Oval Office desk with printouts of models of the storm's path.

"My people just informed me that this is one of the worst storms to hit the East Coast in many years. Also, looking like a direct hit on North Carolina, South Carolina and Virginia. Please be prepared, be careful and be SAFE!" the President tweeted Monday evening, adding that he had spoken by phone with those states' governors, offering the federal government's support.

Was just briefed via phone by @DHSgov @SecNielsen and @FEMA @FEMA_Brock, along with @VP Mike Pence and Chief of Staff, John Kelly on incoming storm which is very dangerous. Heed the directions of your State and Local Officials - and know that WE are here for you. Be SAFE! pic.twitter.com/sN8D5NvrBa — Donald J. Trump (@realDonaldTrump) September 10, 2018

Nielsen and Long will brief Trump again Tuesday in person at the White House, press secretary Sarah Sanders told reporters Monday.

The White House has been in contact with local authorities, Sanders said.

"Lines of communication remain open and the federal government stands ready to assist," she said.

The hurricane has also impacted the President's travel plans: His campaign canceled a campaign rally in Jackson, Mississippi, scheduled for Friday.

The National Hurricane Center upgraded the storm twice Monday, to a Category 4 hurricane. That means sustained winds of at least 130 mph and expectations of catastrophic damage, the hurricane center says.

Learned lessons

Aides say they are applying lessons from last year's spate of storms to an expected repeat season of destruction.

A public face of last year's efforts, Homeland Security adviser Tom Bossert , departed the administration in April. His replacement, Doug Fears, was previously a top White House official responsible for hurricane response efforts, helping to coordinate the government's response to last year's storms from his office in the Eisenhower Executive Office Building.

Other top officials involved in last year's hurricane season, including Long and Nielsen, also remain in place.

That's left administration officials confident in this year's efforts, even as the White House's approach to last year's storms has drawn increased scrutiny. Initially hailed as a rare glimmer of competence in an otherwise chaotic and dysfunctional administration, the administration's hurricane response has since been re-evaluated. Questions have been raised over disparities in how the President responded to storms in Florida and Texas compared to Puerto Rico, where the official death toll was recently revised to nearly 3,000

Trump last month defended his administration's work in Puerto Rico, despite the dramatically increased death count.

"I think we did a fantastic job in Puerto Rico," Trump said during an exchange with reporters at the White House. "We're still helping Puerto Rico."

It was an optimistic accounting of his administration's handling of the natural disaster, which left much of the US territory without power for weeks and resulted in thousands of deaths. The island's governor formally raised the death toll from 64 to 2,975 last month following a study conducted by researchers at George Washington University.

And earlier this month, the Government Accountability Office released a report that revealed that FEMA was so overwhelmed with storms by the time Hurricane Maria hit Puerto Rico that more than half of the workers it was deploying to disasters were known to be unqualified for jobs they were doing in the field.

Long said FEMA made changes to its priorities and procedures following some of those learned lessons.

"We are concentrating on what we call critical lifelines -- health, safety security. You know, we've got food, shelter, health and medical, power and fuel, communications, transportation, hazardous waste," he told reporters on a conference call on Hurricane Lane preparations last month.

Long continued: "We are hyper-focused on those seven critical lifelines because we realized last year that if any one of those lifelines goes down, then life safety is in jeopardy. And so we're reorganizing the firepower of the federal government underneath these critical lifelines, we're pushing forward."

Key positions unfilled

Earlier in the summer, Trump visited FEMA headquarters for a briefing on the hurricane year, a yearly tradition meant to demonstrate a President and administration with a firm handle on the meteorological challenges ahead. Trump spent much of his remarks introducing members of his Cabinet and hailing other areas his administration is succeeding.

He briefly returned to hurricane preparations toward the end of the public section of his appearance.

"We are marshaling every available resource to ensure maximum preparation for rapid response. That's what we had last year," he said.

Still, key positions at FEMA remain unfilled, including a deputy administrator. The White House's nominee is awaiting confirmation in the Senate; a previous pick withdrew his name from consideration in the middle of last year's hurricane season after questions arose about his previous government work.