Tens of thousands of homes and businesses remained without power Monday across South Florida as the remnants of Tropical Storm Isaac continue to wreak havoc for power lines and transformers operated by Florida Power & Light — and triggered flash flood warnings in the afternoon.

Wind-wise, Isaac didn’t amount to much but its stubborn stormy outer bands continued to drench Southeast Florida from Miami to Palm Beach counties on Monday.

The National Weather Service put eastern Broward and Palm Beach counties under a flash flood warning at 1:37 p.m., and said it would be in place until 4:30 p.m. Much of the rest of the coast was under a flood advisory.

“A flood advisory means ponding of water in urban or other areas is occurring or is imminent,” a NWS warning said. “Runoff may also elevate water levels in canals and ditches.”

The additional deluge was coming on top of rain that made Sunday-through Monday morning the wettest 24 hours since Hurricane Mitch in 1998, said Gabe Margasak, a spokesman for the South Florida Water Management District.

Across the district, which stretches from Key West to Orlando, Issac dumped nearly 3.5 inches but some spots in Palm Beach County recorded up to a foot. Sunrise in Broward saw more than six inches. And that was through 6:30 a.m. — not including the squalls that continued to rush across the state from Isaac’s center some 200 miles away.

As the region struggled to return to normal following Isaac’s brush of wind gusts and rain on Sunday, about 70,000 FPL customers were reported to be without power as of noon Monday.

About 29,000 customers (out of 1 million) in Miami-Dade were without power as of 1 p.m., while in Broward nearly 25,000 customers (out of 874,500) were experiencing outages, according to Florida Power & Light. About 20,000 customers (out of 687,000) in Palm Beach were without power. The utility has about 2.4 million customers in the tri-county area, including more than 1 million in Miami-Dade.

FPL crews have been working since Sunday night to repair downed lines and blown transformers, said Peter Robbins, an FPL spokesman, adding that the overnight winds and rains have made work difficult.

“We’ve restored a lot of customers,’’ Robbins said, but added that given Isaac’s continued wind gusts, “We’re not out of the woods yet.’’

In Monroe County, both electric companies servicing the Keys — Florida Keys Electric Cooperative and Keys Energy — reported sporadic outages, but said that crews were able to restore service.

Isaac remains a tropical storm but is forecast to strengthen through the day as it moves through the warm waters of the Gulf of Mexico and heads toward Louisiana and Mississippi.

While South Florida appears to have dodged the worst of Isaac, the region remains under a flood watch until 8 p.m.

The northern Gulf Coast now faces a potential strike from Isaac. Hurricane watches and warnings were in effect for portions of the Louisiana coast, Mississippi, Alabama and the Florida Panhandle.

The National Hurricane Center in Miami forecasts that Isaac will strengthen into hurricane status before making landfall in the northern Gulf Coast early Wednesday with 90- to 95-mile-per-hour winds, a strong Category 1.

The storm is forecast to land close enough to Florida’s Panhandle that Gov. Rick Scott said he will return to Tallahassee Monday, as he expects Isaac to increase wind speeds and become a slow-moving hurricane that will make landfall somewhere between Pensacola and Mobile, Ala., Tuesday night, and dump an estimated 16 inches on the already-soaked Panhandle.