ISLAMORADA -- Florida has battened down the hatches for what could be the first hurricane strike in seven years. Schools were ordered closed. Republicans postponed the national convention in Tampa.

Tourists jammed U.S. 1 out of the Florida Keys. And local TV shifted to endless radar loops of a massive but messy storm called Isaac rolling up the Cuban coast.

At 5 a.m. Sunday, the path remained the same but the storm strengthened a little overnight. With the advisories, the National Hurricane Center made it clear: Isaac, which killed at least three people in Haiti, was going to hit somewhere in the Keys on Sunday, possibly as a 75- to 80-mph hurricane.

Tropical storm winds were expected to begin lashing the islands near dawn and steadily worsen, spreading north across Miami-Dade and Broward counties throughout the day. Four to eight inches of rain could flood already saturated neighborhoods, rough seas and storm surge could spill over roads and docks and there is a heightened risk of tornadoes.

Steve Willis, harbor master at Smugglers Cove Marina in Islamorada, shrugged the threat off early Saturday with characteristic Keys nonchalance. He planned to ride Isaac out on his 37-foot sailboat, while watching over 10 other boats — from a 52-foot charter fishing boat to an 11-foot Zodiac — docked at the marina.

“They are hunkered down pretty good, and with the likely direction of the wind, the [Snake Creek] bridge, sand berms and mangroves will protect this marina,” he said. “But I am worried about Barnacle Bob’s. He could be my problem child.” Barnacle Bob is a floating burger shack, a light, high-sided pontoon boat Willis worried would get whipped around by the wind.

But emergency managers in South Florida were taking no chances on a storm with a wind field more than 200 miles wide. Monroe, Miami-Dade and Broward counties all ordered schools closed Monday, and private schools and universities followed the lead. All three counties also opened shelters and urged residents to stay indoors until the storm passes sometime Monday morning.

Florida Gov. Rick Scott issued a state of emergency, expressing concern about the damage Isaac might do once it passes the Keys and fuels up in the warm Gulf of Mexico. It was forecast to grow into a Category 2 Hurricane with 100 mph winds as it approaches the Panhandle on Tuesday.

Rick Knabb, director of the National Hurricane Center in West Miami-Dade, said that a strengthening Isaac in the Gulf could pose a storm surge threat to Tampa Bay, where the Republican National Convention was scheduled to convene Monday in an area vulnerable to flooding. Events will now be delayed until Tuesday afternoon.

In Miami-Dade, Mayor Carlos Gimenez also issued an evacuation order for people living in mobile homes, unsafe buildings and homes in low-lying, flood-prone areas. The Keys did the same, adding an order for boat dwellers to seek safer shelter.

Even though Broward is not under a hurricane warning, Broward’s director of emergency operations, Chuck Lanza, said Saturday that residents still need to be prepared for damaging tropical storm-force winds.

“I’m putting up my own shutters,” he said. “This is not something to take lightly.”

Though Isaac’s wind weren’t powerful, the huge storm still left a path of death and damage in the Caribbean.

In Haiti, a home collapsed, killing a 10-year-old girl while flooding persisted in quake-battered Port-au-Prince, where the swollen Grise River inundated homes in the poverty-stricken Cite Soleil neighborhood. At least two other deaths were reported and rain was still falling much of Saturday across a country prone to deadly flash floods and mudslides.