KEY WEST -- Big but not bad.

Tropical Storm Isaac huffed and puffed but blew little down other than palm fronds, branches and random trees. It frustrated fliers with hundreds of canceled flights, sunk a few boats in the Keys and sparked scattered power outages across South Florida, imperiling the chili-pepper-flavored ice cream at one Homestead shop. But there were no reports of serious damage or flooding.

Unfortunately, Isaac was not expected to remain meek. The National Hurricane Center expects the sprawling mess of squalls that swept South Florida to morph into a wicked 100-mph storm, possibly stronger, bearing down on the Gulf Coast by Tuesday. Its target remained uncertain but a swath of vulnerable low-lying coastline from the eastern Panhandle to Louisiana, including the city of New Orleans, was under a hurricane watch.

At 5 a.m. Monday, forecasters said Isaac continued to move west-northwest in the warm Gulf of Mexico. Its sustained winds remained at 65 mph, but it was expected to strengthen to a Category 1 hurricane. A new tropical storm warning has been issued for Louisiana's Gulf Coast as Isaac approaches.

For South Florida, under a tornado watch until 9 a.m. and a flood watch through Monday evening, Isaac’s broad tail of rain could continue to remain a headache. Wind gusts of more than 50 mph have been recorded in Broward and 2-3 inches of rain have been recorded in Miami-Dade.

But the storm largely amounted to what Miami-Dade Mayor Carlos Gimenez called a practice run for a region that dodged its first hurricane strike since Wilma in 2005. Forecasters had predicted it might hit the Keys as a Category 1 hurricane.

“It’s a good thing. We prepared for the worst,’’ Gimenez said. “Obviously we’re not going to get the worst. It’s a relief.’’

Though damage appeared to be minimal, school and other closures in Miami-Dade, Broward and Monroe counties remained in place. Emergency managers urged residents to head out cautiously, if at all, so workers could clean up debris and check equipment.

“We always have people get injured or killed post-storm,” Broward Emergency Operations Director Chuck Lanza said.

Outside Key West’s ramshackle Schooner Wharf Bar, a bearded bicyclist pedaled by, wearing a rain poncho and hooting a sentiment about Isaac widely expressed across the Keys, where locals shrugged off the threat.

“It’s not a hurricane,” the cyclist called out. “It’s a windy day in paradise.”

The single damage report to the Monroe County Sheriff’s Department: a tree that fell onto the stairs of an unoccupied home on Big Pine Key.

At St. Mary’s Star of the Sea Catholic Church in Key West, home of the Grotto of Our Lady of Lourdes, where locals have long gone to pray to be spared from hurricane devastation, Father John Baker said, “All we know is, it wasn’t what it could have been. I’m so grateful.”

Isaac left scattered power outages in its wake: In Miami-Dade, 9,730 customers were without power at 10 p.m. Sunday, the latest update that Florida Power & Light reported on its website. In Broward, 6,250 customers were without power and 2,300 Palm Beach residents lost electricity, too.

It also grounded some 760 flights in and out of South Florida: 550 at Miami International Airport and 160 flights at Fort Lauderdale. Key West’s airport was closed all day, forcing cancellation of about 50 flights.