TAMPA, Fla. -- The once-powerful Category 5 Hurricane Irma has now been downgraded to tropical storm, a day after making landfall on Florida.

The storm now has 60 mph winds, according to the 2 p.m. Monday update from the National Hurricane Center. It is moving north-northwest at 17 mph with a minimum central pressure of 980 mb.

Irma is centered about 80 miles south-southeast of Albany, Georgia.

The U.S. National Hurricane Center says Irma is expected to weaken to a tropical depression by Tuesday afternoon.

Photos: Hurricane Irma's damage and destruction

Hurricane Irma officially made U.S. landfall as a Category 4 storm at 9:10 a.m. Sunday at Cudjoe Key. Around that time, there was a reported 106 mph gust at the National Key Deer Refuge on Big Pine Key.

Irma made its second U.S. landfall at Marco Island at about 3:30 p.m.

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A NOAA tide gauge in Naples just measured a water level of 2.2 feet above Mean Higher High Water, which is a 7 foot increase over the past hour and a half.

As the storm plods northward, a tropical storm warning has been issued for Atlanta as Hurricane Irma makes its way toward Georgia.

See Also: 13News Now Hurricane Center

According to USA Today, Irma's landfall at Cudjoe Key, Florida marks the first time two consecutive Category 4 hurricanes have hit the United States, following Hurricane Harvey in Texas last month. Irma is also Florida's first major hurricane since Wilma in 2005.

Here's a breakdown of the Saffir-Simpson scale, according to the National Hurricane Center:

Category 1 - 74-95 mph sustained winds: Very dangerous winds will produce some damage

Category 2 - 96-110 mph sustained winds: Extremely dangerous winds will cause extensive damage

Category 3 - 111-129 mph sustained winds: Devastating damage will occur

Category 4 - 130-156 mph sustained winds: Catastrophic damage will occur

Category 5 - 157 mph or higher sustained winds: Catastrophic damage will occur ("a high percentage of framed homes will be destroyed)

In one of the biggest evacuations ever ordered in the U.S., about 6.3 million people in Florida — more than one-quarter of the state’s population — were told to clear out from threatened areas, and another 540,000 were directed to move away from the Georgia coast.

Gov. Rick Scott ordered all public schools, colleges and universities to close Friday through Monday.

The governor told residents not to become complacent because the storm could have "major and life-threatening impacts from coast to coast."

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Editor's Note: Information from WTSP, USA Today and the Associated Press is used in this story