Forecasters say Isaac is on the verge of becoming a hurricane as it bears down on the northern Gulf Coast.
The U.S. National Hurricane Center said at 5 a.m. EDT on Tuesday that Isaac was still a tropical storm but was likely to become a hurricane during the day as it gained strength over the Gulf of Mexico.
Isaac is expected to make landfall over southeastern Louisiana, possibly the New Orleans area, either late Tuesday or early Wednesday.
The center of the storm was located about 125 miles south-southeast of the mouth of the Mississippi River. It has top sustained winds of 70 mph and is moving to the northwest at 12 mph.