The U.S. Army Corps of Engineers was working to close the barge gate of the Lake Borgne Surge Barrier Thursday afternoon in response to a potential tropical storm forming in the Gulf of Mexico.

Closing the gate, a nearly four-hour process that was expected to wrap up by early evening, is the first step in preparing the post-Hurricane Katrina flood protection system for a storm.

The surge barrier is a 1.8-mile long, 25-foot high wall that crosses the Golden Triangle Marsh near Lake Borgne, connecting flood protection features in New Orleans East to those in St. Bernard. The barrier crosses both the Gulf Intracoastal Waterway and the Mississippi River-Gulf Outlet.

The 150-foot wide barge gate on the Gulf Intracoastal Waterway involves swinging a barge into an opening in the barrier and sinking it. That gate is one of three that allows access through the barrier and the corps’ procedures call for it to be closed if a storm has the potential to strike the New Orleans area within 96 hours.

“If there’s a possibility of it, we’re going to close it,” corps spokesman Ricky Boyett said.

The corps will make decisions on whether to close other elements of the flood protection system based on what kind of storm surge, if any, is expected in the area.

A low-pressure system near the Yucatan Peninsula has about a 50 percent chance of becoming a tropical cyclone in the next two days and a 60 percent chance of becoming a tropical cyclone over the next five days, according to a National Hurricane Center forecast released at 2 p.m. Thursday.