In its latest update at 03:00 GMT Monday, the National Hurricane Center (NHC) says "hurricane conditions are continuing across portions of the central Florida peninsula".
And more than 120 homes were being evacuated early Monday in Orange County, just outside the city of Orlando, as floodwaters started to pour in.
Now a category 3 storm, it may be a category 4 by the time it makes landfall in South Florida Sunday morning.
Florida emergency management officials say at least 51,000 residents have hunkered down in approximately 300 shelters ahead of Irma.
She described the confluence of the storm surge, more than 10 inches of rain, and winds from the south pushing water upstream on the river as a "trifecta effect".
Boone Electric Cooperative sends team to help with Irma relief
These outage numbers continue to decrease, and highlight the resilience, preparedness and collaboration of electric cooperatives. In 1989, when the Category 4 Hurricane Hugo struck SC , power was knocked out to more than 227,000 residences and businesses.
Irma, which killed at least 22 people in the Caribbean, was likely to cause billions of dollars in damage to the third-most-populous USA state.
Irma struck as a Category 4 but by midafternoon had weakened to a Category 3 with still-fearsome 120 miles per hour winds and heavy rain. Its ferocity as it bore down on hurricane-prone Florida prompted one of the largest evacuations in US history.
"This is your last chance to make a good decision", Gov. Rick Scott warned residents in Florida's evacuation zones, which encompassed a staggering 6.4 million people, or more than 1 in 4 people in the state. Jonathan Brubaker, 51, waited out the storm bunkered in a recently constructed house in Bradenton, on the state's west coast, with hurricane shutters drawn, flashlights and candles ready.
The area in orange around Irma shows the wind field for hurricane force winds. He still had power. "We have for 90 years avoided this day, but I think our day has come".
After leaving millions without power across the state of Florida, the storm's winds have felled trees and power lines across Georgia.
Miami International Airport, one of the busiest in the country, halted passenger flights through at least on Monday.
Helicopter crash that killed Troy Gentry caused by engine problems
Gentry was still alive when rescue workers cut him from the wreckage, but he died a short time later at Virtua Hospital Marlton. The company flight instructor and another flight instructor tried to help the pilot find the best method of landing.
The storm has weakened to a tropical storm with 70 miles per hour winds, according to the 8 a.m. Monday update from the National Hurricane Center. But some around Florida are choosing to stay, a rite of passage for many in the state who boast about the storms they weathered: Camille, Andrew, Katrina and others.
One death in Florida, that of a man killed in an auto accident during the storm, was blamed on Irma.
CNN's Derek Van Dam, reporting from Miami Beach, said the roaring winds felt like a jet engine. The HobNob Kitchen and Bar boarded up their window with a sign that says "Go away George.' Hurricane George was back in 1998, and they had no time to even change the name on the sign". "It's like being on a ship".
More than 800,000 were without power in Miami-Dade County.
But the latest travel advice issued by the Government states: 'Across the United States, it is important that you follow the advice of the local authorities, including any evacuation orders.
The Tampa Bay area feared a direct hit from a major hurricane, but ended up getting more of a sideways swipe from a weakened Irma.
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