(CNN) -- Hurricane Isaac got more powerful Tuesday afternoon and, as of 4 p.m. CT (5 p.m. ET), had sustained winds of 80 mph, the National Hurricane Center reported. "Isaac (is) getting better organized as it nears southeastern Louisiana," the center said. Isaac's eye was about 30 miles south-southwest of the mouth of the Mississippi River and 105 miles south-southeast of New Orleans, with hurricane-force winds measured 60 miles out from its center.