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Hurricane Irma weakens to Category 1 as it heads to Florida's interior, but remains dangerous

Hurricane Irma continued to hammer Florida early on Monday, after slamming the Keys in the morning and pummeling Miami, Naples and other areas throughout Sunday.

But the storm was losing strength as its center moved toward the northwestern coast of the Florida Peninsula and was forecast to weaken to a tropical storm during the day and to a tropical depression by Tuesday afternoon, the U.S. National Hurricane Center (NHC) said.

Irma, once ranked as one of the most powerful hurricanes recorded in the Atlantic, was about 60 miles (100 km) north of Tampa, Florida, carrying maximum sustained winds of 75 miles per hour (120 km per hour), the center said in a 5 a.m. ET advisory.

Irma's center would cross the eastern Florida Panhandle into southern Georgia on Monday afternoon, then move through southwestern Georgia and eastern Alabama on Monday evening and Tuesday, the NHC forecast.

A Category 1 story has sustained winds of 75-95 miles per hour, or 119-153 kilometers an hour. It's considered very dangerous, with large tree branches potentially snapping and shallowly rooted trees possibly toppling. Well-constructed houses could also see roof damage.

It noted that Irma has a very large wind field with hurricane-force winds extending outward from up to 80 miles, or 130 km, from the center of the storm, while tropical-storm-force winds extended outward for up to 415 miles, or 665 km.

Wind gusts of hurricane force were reported at Orlando International airport, it said. Orlando is around 85 miles from Tampa.

The center of Irma was becoming less well defined on National Weather Service Doppler radar data, the NHC noted.

Irma had approached the Tampa Lakeland area as a Category 2 hurricane, the NHC update at 12 a.m. ET on Monday said.

On the Saffir-Simpson hurricane wind scale, Catagory 2 winds are between 96-110 miles per hour, or 154-177 kilometers per hour. It is considered extremely dangerous and capable of extensive damage, including snapping or uprooting shallowly rooted trees and potential major damage to homes.

The Tampa area has not seen a hurricane in roughly 90 years. Tampa City Mayor Bill Buckhorn told his constituents Tampa was about to be "punched in the mouth" by the storm. The city, like others, instituted a curfew to keep citizens off the streets while emergency and rescue crews do their work.

Flooding in the Brickell neighborhood as Hurricane Irma passes Miami, Florida, U.S. September 10, 2017.
Stephen Yang | Reuters
Flooding in the Brickell neighborhood as Hurricane Irma passes Miami, Florida, U.S. September 10, 2017.

Irma is one of the most powerful hurricanes to hit the United States in a century. It spent more than eight days as a major hurricane, which is any hurricane rated Category 3 to 5 on the Saffir-Simpson scale, said Colorado State University meteorologist Philip Klotzbach in a tweet.

It first made landfall in the U.S. as a Category 4 hurricane in the Florida Keys at 9:10 a.m., Sunday morning, then again as a Category 3 at Marco Island in the afternoon. Shortly thereafter, it was downgraded to a Category 2, with wind speeds of 110 mph.

Almost 150,000 people in Florida were reported to be in shelters, and up to nearly 2 million people were without power in the state.

—Reuters contributed to this report.