An 18-mile stretch of a levee in southeastern Louisiana was overtopped early Wednesday by surges from Hurricane Isaac as it made its slow move onshore. Officials in Plaquemines Parish said the Coast Guard is attempting to rescue two men stranded on top of one levee and others trapped in houses. Isaac made its first landfall at 8 p.m. Tuesday night before moving back out to the Gulf of Mexico for a few hours and eventually making a second landfall near Port Fourchon, La., around 4 a.m. The National Hurricane Center warned of storm surges of 6 to 12 feet in Mississippi, and several feet in other areas along the Gulf Coast. A 10-foot storm surge was already reported in Shell Beach, La. At least 500,000 were left without power in southeast Louisiana.