ORANGE BEACH, Ala. — Hurricane Sally drifted in a slow crawl Tuesday toward the northern Gulf Coast, threatening dangerous storm surge and relentless rainfall that forecasters warned could trigger historic flooding as the storm was expected to hover in the area long after coming ashore.

“It’s going to be a huge rainmaker,” said Phil Klotzbach, a research scientist and meteorologist at Colorado State University. “It’s not going to be pretty.”

The National Hurricane Center expects Sally to remain a Category 1 hurricane, with top sustained winds of 80 mph (130 kph) when it makes landfall late Tuesday or early Wednesday. The storm’s sluggish pace made it harder to predict exactly where its center will strike, though it was expected to reach land near the Mississippi-Alabama state line.

The hurricane’s slow movement not only delayed landfall, but also exacerbated the threat of heavy rain and storm surge. Sally remained a dangerous storm Tuesday even after losing power, its fiercest winds having dropped considerably from a peak of 100 mph (161 kph) on Monday.

By late morning Tuesday, hurricane warnings stretched from east of Bay St. Louis, Mississippi, to Navarre, Florida. Rainfall of up to 20 inches was forecast near the coast. There was a chance the storm could also spawn tornadoes and dump isolated rain accumulations of 30 inches.

Two large casino boats broke loose Tuesday from a dock where they were undergoing construction work in Bayou La Batre, Alabama. M.J. Bosarge, who lives near the shipyard, said at least one of the riverboats had done considerable damage to the dock.

“You really want to get them secured because with wind and rain like this, the water is constantly rising,” Bosarge said. “They could end up anywhere. There’s no telling where they could end up.”

In Orange Beach, Alabama, towering waves crashed onshore Tuesday as Crystal Smith and her young daughter, Taylor, watched. They drove more than an hour through sheets of rain and whipping wind to take in the sight.

“It’s beautiful, I love it,” Crystal Smith said. “But they are high. Hardly any of the beach isn’t covered.”

Capt. Michael Thomas, an Orange Beach fishing guide, was outside securing boats and making other last-minute preparations. He estimated up to 5 inches of rain had fallen in as many hours.

“I’m as prepared as I can be,” Thomas said.

A couple miles away in Gulf Shores, Alabama, waves crashed over the end of the long fishing pier at Gulf State Park. Some roads in the town already were covered.

Stacy Stewart, a senior specialist with the National Hurricane Center, said Tuesday that people should continue to take the storm seriously since “devastating” rainfall is expected in large areas.

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