Tropical Storm Isaac was on the verge of becoming a hurricane as it approached the Gulf Coast early Tuesday morning, forecasters warned.

Its swirling winds and rain will be a major test of the region’s new flood control systems seven years after Hurricane Katrina sent walls of water crashing inland.

The U.S. National Hurricane Center said at 8 a.m. ET on Tuesday that Isaac was still a tropical storm but was likely to become a hurricane during the day as it gains strength over the Gulf of Mexico.

The center of the storm was located about 105 miles south-southeast of the mouth of the Mississippi River and had top sustained winds of 70 mph, the Hurricane Center said.

Isaac was expected to make landfall over southeastern Louisiana either late Tuesday or early Wednesday.

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