Karl Breaux didn't have to listen to the weather forecast to know a hurricane may be on its way to the Gulf Coast. His store shelves said it all.

"Our battery rack is selling double, maybe triple what we usually sell," Breaux, who owns Breaux's Mart in Lafayette, La., said Monday. "Water is selling as fast as we put it out. And I tell you what, flashlights will be a commodity around here tomorrow."

Residents across the Gulf Coast boarded up their fishing camps and homes and stocked up on necessities as Tropical Storm Isidore threatened to hit Louisiana or Texas sometime this week.

For most of Monday, Isidore churned over Mexico's Yucatan Peninsula, where it tore off roofs, cut communications and left at least two people dead.

By Tuesday morning, it was back over open water in the Gulf of Mexico. Sustained winds were at 50 mph, but likely would regain hurricane strength of at least 74 mph, forecasters said.

Forecasters were trying to pinpoint what areas on the U.S. Gulf Coast faced the greatest threat, center forecaster Michael Formosa said Tuesday morning. The storm was beginning to turn northward, and a hurricane watch was likely to be issued for Louisiana later in the day, he said.

High seas were expected all across Louisiana's low-lying coast because of the sprawl of the huge weather system. Coastal flood advisories were posted from south Texas to Bay St. Louis, Miss.

Forecasters warned that a strengthening Isidore could be 100 miles south of Louisiana's Vermilion Bay by noon Thursday.

Officials on the marshy coast around the south-central Louisiana bay scrambled to assess the threat.

"It looks like we might need to do some evacuations," said James Anderson, director of emergency preparedness for Iberia Parish.

Isidore could become a Category 2 hurricane with up to a 120 mph winds, pushing sea surge up to 16 feet, Anderson said. Crews were already moving sandbags into central locations for residents to use, he said.

Texas officials took similar precautions.

The National Weather Service posted flooding alerts from Brownsville, Texas, about 90 miles north to Baffin Bay, as coastal residents rushed to stock up on plywood to protect their windows from hurricane-force wind.

"Extra sandbags, generators, it's all up front -- also batteries, flashlights," said Linda Weston, a manager at the Home Depot in Harlingen. "We've ordered extra. The main company in Atlanta is ordering extra materials as well."

Louisiana Gov. Mike Foster declared a state of emergency as a precaution, opening the way for state help if flooding and winds cause more damage than local crews can handle.

Bob Rickles was one coastal resident who wasn't taking any chances. He moved his shrimp boat north 45 miles.

"As soon as they got a storm in the Gulf, we take off and go someplace else," the Grand Isle, La., resident said.