GULFPORT, Miss. — Tropical Storm Isaac is continuing its west-northwest track over the eastern Gulf of Mexico, posing a significant storm surge threat to the northern Gulf Coast.

At its present track, Isaac will make landfall late Tuesday or early Wednesday, according to the National Hurricane Center's 1 p.m. advisory. Where it will make landfall is still unclear, but meteorologists predict it will become a Category 1 or 2 hurricane. Currently, Louisiana and Mississippi are in the cone of uncertainty, and heavy wind, rain and storm surge are expected.

Isaac has sustained winds of 65 mph and is moving at 14 mph. Officials expect a gradual decrease in its forward speed. The storm is churning toward Louisiana.

South Mississippi continues to be under a hurricane warning as are portions of Alabama, Louisiana and Florida.

Heavy rains are expected to deluge South Mississippi as Isaac makes its way through the area, with as a much as 15 inches of rain expected.

"That becomes a terrible concern for us," said Rupert Lacy, director of Harrison County's Emergency Management Agency. "If that rain hits all of Harrison County, that means we are going to have inland flooding. Roads and areas that like that are going to be impassable."

Forecasters said residents should prepare for heavy winds and a strong storm surge no matter where Isaac touches ground.

Gov. Phil Bryant on Sunday declared a state of emergency as did several South Mississippi cities and counties. Harrison County, Pass Christian and Gulfport all declared states of emergency monday morning.

No mandatory evacuations have been ordered, though emergency managers are urging residents in low-lying areas to consider moving to higher ground. Lacy said shelters may open Tuesday morning, depending on the track and intensity of the storm.

Schools along the Coast are open Monday but will be closed Tuesday and Wednesday. Mississippi Gulf Coast Community College, Pearl River Community College and the University of Southern Mississippi Gulf Coast will be closed Tuesday and Wednesday.

EMA officials stressed that it is still too soon to say for sure where the storm will touch ground. Either way, they said, South Mississippi will feel the effects of Isaac's heavy rains, winds and storm surge.

Most South Mississippi residents and businesses started preparing for the storm Sunday, with the work continuing Monday.

Officials at the Ohr-O'Keefe Museum of Art started packing up their collection Sunday and were finishing up this morning. They expected a moving truck in at noon Monday to move the collection to a safe location during the storm.

At Souvenir City in Biloxi, workers started boarding up their windows Monday. The business was destroyed in Hurricane Katrina and rebuilt in 2009. The store's owner, J.J. Pierotich, said he's encouraged by the storm's latest westward movement and boarding up the business "is a good drill for us."

More than 50 percent of the boats at the Biloxi Small Craft Harbor had been already been moved Monday morning.

Many beach vendors had removed their personal watercrafts, chairs and other wares Sunday though some were still packing up supplies Monday.

Construction crews gathered up their supplies Monday on the Harrison County sand beach, where handicapped structures are being built. "We're just trying to make sure the storm doesn't take it."

At Naval Construction Battalion Center Gulfport, officials said there was no evacuation planned for base housing. Instead, officials encouraged everyone to stay in their homes beginning Tuesday morning.

NCBC residents will be able to go to shelters if necessary and shuttle service will be open until 8 p.m. Tuesday to take residents to area shelters. No pets are allowed at the shelters, though Harrison Central High School is sheltering pets. The commissary, Mini-Mart and NEX will close Tuesday, but were open Monday. The Ombudsman lunch Monday and the Woman's Equality program Wednesday have been cancelled. All non-essential personnel are released at the close of business Monday.

Sun Herald photo journalist John Fitzhugh contributed to this report.