GULFPORT — Tropical Storm Isaac began lashing the Florida Keys late Sunday morning, and though its wind speed had lessened a bit, emergency officials are urging South Mississippi residents to prepare now in case Isaac decides to make landfall along the Mississippi Coast, possibly Wednesday morning.

The latest advisory from the National Weather Service at 1 p.m. Sunday showed Isaac’s maximum sustained winds of 65 mph had lessened to 60 mph, and the storm was about 80 miles southeast of Key West, Fla., moving west-northwest at 18 mph.

A tropical storm is considered a hurricane when it reaches maximum sustained winds of 74 mph, and officials believe the storm could reach hurricane strength later Sunday, becoming a Category 1 or Category 2 hurricane.

Its coordinates were 23.9 North and 81.5 West.

The latest update indicates the center of Isaac will move near or over the lower Florida Keys by Sunday night and move into the Gulf of Mexico on Monday.

Isaac could effect the Mississippi Coast by Tuesday, but where it will make landfall remains unclear.

Biloxi city officials are working under the assumption that the present model indicates it will make landfall in Biloxi or the general vicinity about 8 a.m. Wednesday.

The Hurricane Center has extended its hurricane watch from the Florida Keys and westward to just east of Morgan City, La., which includes New Orleans.

The next 12 to 24 hours will be a critical time for watching where Isaac appears to be heading, said Harrison County Emergency Manager Rupert Lacy.

“Within the next day, we will get a better idea of where it decides to make its presence known,” he said. “We’re not out of the woodshed yet, but people who have not started making plans should seriously think about it now.”

That includes plans for possible evacuation, gathering emergency food and water supplies and securing loose property outdoors that could become a flying projectile.

With hurricane models showing the projected path turning a bit west, South Mississippi residents need to take the possibility of landfall here seriously, Lacy said.

“It’s a beautiful day, and it’s a great time to go ahead and make preparations. Don’t let your guard down. If it starts to turn crappy, so be it. We will move forward with whatever we have to deal with.”

Lacy issued a flood warning Sunday for the Tchoutacabouffa and Wolf rivers. The flood stage for each is 8 feet, but both are expected to crest at 9.5 feet Wednesday.

City officials in Ocean Springs set up a self-serving sand bag area at 712 Pine Drive, with plans to open it up at 3 p.m. Sunday.