However, Isaac could bring some relief to places farther inland where farmers have struggled with drought. It also may help replenish a Mississippi River that has at times been so low that barge traffic is halted so engineers can scrape the bottom to deepen it.
Forecasters predicted Isaac would intensify into a Category 2 hurricane, with winds of about 100 mph, by early Wednesday around the time it's expected to make landfall. The current forecast track has the storm aimed at New Orleans, but hurricane warnings extended across 280 miles from Morgan City, La., to the Florida-Alabama state line. It could become the first hurricane to hit the Gulf Coast since 2008.
Evacuations were ordered for some low-lying areas and across the region, people boarded up homes, stocked up on supplies and got ready for the storm. Schools, universities and businesses closed in many places.
Still, all the preparation may not matter if flooding becomes the greatest threat. In Pascagoula, Miss., Nannette Clark was supervising a work crew installing wood coverings over windows of her more than 130-year-old home. But she said all that won't matter if a storm surge reaches her home, as it did after Katrina in 2005.
"The water was up to the first landing of the stairs," she said. "So I get very nervous about it."
Isaac's approach on the eve of the Katrina anniversary invited obvious comparisons, but Isaac is nowhere near as powerful as the Katrina was when it struck on Aug. 29, 2005. Katrina at one point reached Category 5 status with winds of over 157 mph. It made landfall as a Category 3 storm and created a huge storm surge.