GULFPORT (AP) — Isaac inundated low-lying areas along Mississippi’s Gulf Coast on Wednesday as hurricane-driven water rose several feet in some spots while thousands waited out the storm in shelters.

Hancock County Emergency Management Director Brian Adam said the water stood up to 4 feet deep in many low-lying areas of Hancock County and was still rising while the vast storm system lumbered off the mouth of the Mississippi River.

“It’s flooding in quite a bit of places,” Adam said, citing reports from Pearlington, Lakeshore and parts of Waveland and Bay St. Louis.

Police waved drivers off U.S. 90, the main beach road in Gulfport, because of flooding. A billboard had torn loose and water stood foot-deep in some areas, knee-deep elsewhere.

Adam said crews successfully rescued three people who had called for help after a houseboat broke loose in Pearlington, near the Louisiana state line but had no major incidents to report immediately.

Hancock County is unusually vulnerable to storm surge because water driven into the Mississippi Sound piles up against the V-shape coast where Louisiana and Mississippi come together. Adam said he wasn’t sure if any structures had been damaged. Most buildings destroyed by 2005’s Hurricane Katrina in Hancock County were elevated when rebuilt.

American Red Cross spokesman Jay Huffstatler said nearly 2,000 people had entered a total of 33 shelters in Mississippi.

“We’ve had a great turnout at shelters, people are taking the storm seriously,” Huffstatler said.

In Jackson County, Monica Cooper, a spokeswoman for the emergency management agency, was currently reporting 80 flooded roads and reports were increasing “steadily.”

She said low lying areas of Moss Point, Gautier and St. Martin were among the hardest hit with flooding. She said the flooding was a combination of heavy rainfall and storm surge.

Cooper said she could not confirm reports that some homes had flooded.

“But with the extent of the flooding I would not be surprised,” she said.

In Pass Christian, a coastal community that had been wiped out by hurricanes Camille and Katrina, Mayor Chipper McDermott was optimistic Isaac would not deal a heavy blow.

“It’s not too bad, but the whole coast is going to be a mess,” he said early Wednesday.

McDermott stood on the porch of the $6 million municipal complex built after Katrina wiped out the city seven years ago today. Its walls are made of 1-foot-thick concrete to withstand hurricane winds.

The mayor lamented that Isaac arrived on the anniversary of Katrina, and said the Hancock County city’s recovery had been going well.

As he looked out toward the Gulf of Mexico, pieces of a structure that had stood atop the city’s fishing pier washed across the parking lot.

An American flag was flapping wildly in the wind and traffic lights leading into the parking lot flashed as a TV news crew tried to do a live shot.

McDermott said low-lying areas that typically flood were under water. The area has been under a mandatory evacuation. McDermott said many homes there are vacation getaways for New Orleans residents so he thought they were empty as Isaac neared.

The state transportation officials said Mississippi Highway 43 and Mississippi Highway 604, both in Hancock County, were not passable because of storm surge driven inland.

In Biloxi, the eastern end of the city, a point that juts into Biloxi Bay where most casinos are located, was being threatened by rising water, authorities had said earlier. They cautioned that the high tide wasn’t expected until midmorning — a critical time as Isaac hung off the nearby coast of southeastern Louisiana.

By dawn, casinos remained mostly dry. Nonetheless, there was water in the bottom floor of Grand Casino’s closed-off parking garage. And water lapped around the Palace Casino in East Biloxi.

Tornado warnings had been posted, meanwhile, because of thunderstorms in southern Mississippi. And the back streets of some communities, on higher ground, showed little evidence of Isaac’s passage save for some downed tree branches.

Power outage totals in Mississippi remained below 10,000. Coast Electric Power Association said about 4,000 customers were without power when it called in crews after 10 p.m. because of unsafe conditions. Singing River Electric Power Association also reported about 1,500 customers with the lights out, mostly in Pascagoula.

Mississippi Power Co. spokesman Jeff Shepard says about 3,600 customers were without power as of 5:30 a.m. CT. He said the majority of the outages were being reported in Biloxi.

He said Mississippi Power crews will begin assessing system damage at 6 a.m.

Pascagoula City Councilman Frank Corder said the power went out at his house after 1 a.m. Wednesday. He said the area had been hit by “occasional gusts and rain, but not too bad so far.”

Despite fears that Isaac could dump a deluge on the already soggy Mississippi coast, rain totals have been relatively light so far. Less than an inch had been reported just after midnight Wednesday in Gulfport, Biloxi and Pascagoula.

Winds rose above 20 mph Tuesday afternoon and stayed there through midnight. A gust of 43 mph was recorded at Gulfport-Biloxi International Airport just after midnight, the worst yet recorded there.

The Mississippi Department of Transportation said beachside U.S. 90, a major thoroughfare, was flooding in several locations in Harrison County, though the agency’s functioning traffic cameras showed the road to be passable.

Before Isaac had even reached the Gulf coast, Mississippi Gov. Phil Bryant and other officials were warning residents not to get complacent about Isaac. Authorities had warned of the threat of significant flooding even hundreds of miles inland in coming days.

“This is a slow-moving system and we expect heavy rain to occur throughout Mississippi,” said Federal Emergency Management Agency Administrator Craig Fugate, speaking Tuesday with Bryant at a Mississippi Air National Guard base in Gulfport. “This is not just a storm for coastal Mississippi.”

Isaac made landfall at 6:45 p.m. CDT Tuesday in Plaquemines Parish, La.

As Isaac pushed closer to shore Tuesday, bands of rain pelted the Mississippi coast. Harbors were mostly empty, other than disabled boats that couldn’t be moved. In Pass Christian, a sail boat had washed aground near the beach and bobbled in the surf. Many houses were boarded up.

The Mississippi Gaming Commission on Tuesday ordered Harrison County’s 10 casinos shut on Tuesday, following the Monday closure of Hancock County’s two gambling halls. Many businesses were closed, and postal workers wrapped mailboxes in plastic.