Irma continued its march north on Monday morning, dumping rain across the width of Florida and lashing the state with powerful winds that downed power lines and left millions in the dark.
The National Hurricane Center said that Irma had weakened to a tropical storm but cautioned that it was still capable of throwing off wind gusts that were near hurricane force.
Losing some of its deadly strength but retaining its vast size, the storm stretched from Florida’s Gulf Coast to the Atlantic as it churned past Tampa. Officials in Tampa lifted the city’s curfew at 8 a.m. amid early assessments showing some debris, minimal flooding and no major damage.
Irma came ashore on the mainland as a Category 2 hurricane, flooded parts of downtown Miami and knocked over construction cranes there as winds exceeded 100 miles per hour.
• As of 8 a.m., the storm had maximum sustained winds of 70 miles per hour and was moving north northwest about 30 miles northeast of Cedar Key, Fla., a small island city near the state’s northwest coast.
• Forecasters expect it to stay inland over Florida as it heads into Georgia, before moving on to Alabama and Tennessee.
• At least four people in Florida have been killed by the storm. It has left at least 27 people dead across the Caribbean.
• The National Weather Service reported Monday that flooding from a storm surge in Jacksonville had exceeded an all-time record set by Hurricane Dora in 1964.
• As many as 5.8 million customers are without power across Florida. The full extent of the damage is not yet known.
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Mayor Bob Buckhorn of Tampa, who on Sunday warned residents that the city was about to get “punched in the face,” said on Monday that the city had been spared the storm’s worst.
“It’s looking good,” Mr. Buckhorn said. “The first blush is that not only did we dodge a bullet, but we survived pretty well. Not a lot of flooding. Tree removal, debris — don’t want to say it’s negligible, but it’s manageable.”
The city was again spared from a direct hit by a hurricane, as has been its good fortune for more than 90 years running. How? “Because we live good lives, because we only get drunk once in a while,” Mr. Buckhorn joked. “No, I don’t have an answer for that.”
Suddenly, the water went away. In the Bahamas, in Tampa Bay and in Naples, observers were shocked to see the waters that usually lap against the shore recede into the distance.
On social media, people reacted with incredulity, noting that the water had disappeared where whitecaps were just hours before on Sunday in Tampa Bay. James Spann, an Alabama meteorologist and weather blogger, reacted sternly to a photograph on Twitter of people playing in the sand exposed by the retreating water.
“The water will come rushing back with a vengeance,” Mr. Spann said on Twitter. “They won’t have time to get out when it begins.”
On Twitter, Gov. Rick Scott issued an urgent warning to stay away from the water. “DO NOT GO IN. The water will surge back & could overtake you.”
Chris O’Donnell, a reporter with The Tampa Bay Times, later reported that the police had cleared people from the shore well before the water came back.
The phenomenon of water being drawn off by the power of Hurricane Irma is known as a negative surge. As Mr. Spann warned, that odd condition will not last — and will become dangerous. Michael R. Lowry, a scientist with the University Corporation for Atmospheric Research, a nonprofit education consortium, explained in a series of tweets that staying away from the water in this storm is important because the hurricane is sending a dangerous surge ashore: 10 to 15 feet, for instance, in Naples, Fla.
And as the National Hurricane Center explained, the water will come rushing back to Naples after the eye passes. On Twitter, the center warned: “MOVE AWAY FROM THE WATER!”
Irma’s center passed over Naples around 5 p.m., the hurricane center said, and continued up the Gulf Coast. For the better part of an hour as it neared Fort Myers, winds that earlier had seemed to fluctuate wildly became far steadier and stronger, spitting rain violently.
Only the sound varied — at times a muffled rattling, other times a rumbling roar.
Then, shortly after 7 p.m., the winds began to wind down and the rain stopped hitting with such force. Within about 10 minutes there was almost no rain at all, and the palm fronds that moments before were streaming horizontally were now waving in a light breeze. Even though dusk was approaching, the sky lightened considerably.
It stayed that way for about 20 minutes, long enough for a few people at one Fort Myers hotel to sneak outside, marvel at the calm, and breathe in the tropical air.
Then the wind started to pick up again, blowing in the opposite direction.