South Florida is bracing for a major storm surge and powerful winds even as Hurricane Irma weakened to a Category 4 storm as it races toward the U.S. mainland.

“Obviously Hurricane Irma continues to be a threat that is going to devastate the United States,” Federal Emergency Management Agency Administrator Brock Long said at a press conference Friday morning. “We’re going to have a couple rough days.”

Irma was downgraded from a Category 5 to a Category 4 storm early Friday morning. As of 8 a.m. Eastern Time, the storm was moving 16 mph and located 450 miles southeast of Miami.

The National Weather Service cautioned Irma is still “extremely dangerous” with maximum sustained winds of 150 mph, which are strong enough to uproot trees, bring down power poles and rip off the roofs and some exterior walls of well-built frame homes.

Hurricane Irma is expected to make landfall in South Florida around 3 or 4 a.m. on Sunday as of Friday’s early morning update.

The National Weather Service issued its first hurricane warnings for Florida overnight, warning residents that “preparations to protect life should be rushed to completion.”

Mandatory evacuation orders have been issued for barrier islands, coastal communities, low-lying areas and mobile homes across Florida, including in Brevard, Broward, Collier, Indian River, Martin, Miami-Dade, Monroe, Palm Beach and St. John’s counties. ABC News estimates roughly 1.2 million Florida residents have been ordered to evacuate.

Meteorologists expect Irma will approach the Florida Keys and southern Florida late Saturday night as a strong Category 4 hurricane and then make landfall near Miami on Sunday sometime around 3 or 4 a.m. Eastern Time. Overnight projections of Irma’s path showed less of a threat to the Carolinas as the monster storm appears likely to move directly up the middle of Florida and curve inland.

Hurricane and storm surge warnings for Florida as of early Friday, Sept. 8, 2017.

Meteorologists predict Irma will continue to weaken as the storm moves inland Sunday into Monday. Irma will approach Orlando on Monday around 2 a.m. Eastern Time still as a major hurricane with winds of about 105 mph. After moving over Orlando, Irma should weaken rapidly to a tropical storm later Monday as it moves across state lines into Georgia, meteorologists say.

The worst of Irma’s winds and storm surge are projected to be near Marathon and Key Largo, but meteorologists say Miami and heavily populated southeastern Florida will still be on the strongest side of the storm.

Southern Florida is likely to receive 6 to 10 inches of rain and up to 20 inches locally from Hurricane Irma.

The National Weather Service on Friday morning issued a storm-surge warning for the Florida Keys and the Jupiter Inlet southward around the Florida peninsula to Bonita Beach, saying there is “danger of life-threatening inundation from rising waters moving inland from the coastline, during the next 36 hours.”

Moreover, heavy rains are forecast to drench northern Florida, Georgia and even possibly South Carolina and Tennessee by Tuesday. Rainfall accumulations in southeast Florida and the Florida Keys are expected to reach 10 to 15 inches, with totals up to 20 inches locally. Eastern Florida, up the coast to Georgia, is expected to receive 8 to 12 inches, according to the National Weather Service.